pytorch/test/distributed/test_c10d_common.py

# Owner(s): ["oncall: distributed"]

import copy
import os
import pickle
import subprocess
import sys
import tempfile
import threading
import time
import unittest
from contextlib import nullcontext
from dataclasses import dataclass
from datetime import timedelta
from itertools import product
from sys import platform
from typing import Optional

import torch
import torch.distributed as dist


if not dist.is_available():
    print("distributed package not available, skipping tests", file=sys.stderr)
    sys.exit(0)

import torch.distributed.algorithms.ddp_comm_hooks.powerSGD_hook as powerSGD
import torch.distributed.distributed_c10d as c10d
import torch.nn.functional as F
import torch.testing._internal.common_utils as common
from torch import nn
from torch.nn.parallel import DistributedDataParallel
from torch.testing._internal.common_distributed import (
    MultiProcessTestCase,
    skip_if_lt_x_gpu,
)
from torch.testing._internal.common_utils import (
    instantiate_parametrized_tests,
    IS_FBCODE,
    IS_SANDCASTLE,
    load_tests,
    parametrize,
    retry_on_connect_failures,
    run_tests,
    TEST_WITH_DEV_DBG_ASAN,
    TestCase,
)
from torch.utils.checkpoint import checkpoint


if TEST_WITH_DEV_DBG_ASAN:
    print("Multiprocessing spawn is not compatible with dev/dbg asan", file=sys.stderr)
    sys.exit(0)

# load_tests from common_utils is used to automatically filter tests for
# sharding on sandcastle. This line silences flake warnings
load_tests = load_tests

if platform == "darwin":
    LOOPBACK = "lo0"
else:
    LOOPBACK = "lo"

torch.backends.cuda.matmul.allow_tf32 = False


def gpus_for_rank(world_size):
    """Multigpu tests are designed to simulate the multi nodes with multi
    GPUs on each node. Nccl backend requires equal #GPUs in each process.
    On a single node, all visible GPUs are evenly
    divided to subsets, each process only uses a subset.
    """
    visible_devices = list(range(torch.cuda.device_count()))
    gpus_per_process = torch.cuda.device_count() // world_size
    gpus_for_rank = []
    for rank in range(world_size):
        gpus_for_rank.append(
            visible_devices[rank * gpus_per_process : (rank + 1) * gpus_per_process]
        )
    return gpus_for_rank


class AbstractTimeoutTest:
    def _test_store_timeout(self, backend, init_method, c2p):
        try:
            dist.init_process_group(
                backend=backend,
                init_method=init_method,
                world_size=1,
                rank=0,
                timeout=timedelta(seconds=1),
            )
            default_store = c10d._get_default_store()
            tik = time.time()
            with self.assertRaisesRegex(RuntimeError, "(?i)timeout"):
                default_store.get("nonexistent key")
            tok = time.time()
            dist.destroy_process_group()
            c2p.append(float(tok - tik))
        except RuntimeError as e:
            # catch "Address already in use" error and report it to the main
            # thread
            c2p.append(e)

    def _init_methods(self):
        f = tempfile.NamedTemporaryFile(delete=False)
        if sys.platform == "win32":
            yield "file:///{}".format(f.name.replace("\\", "/"))
            f.close()
        else:
            yield f"file://{f.name}"
            f.close()
            yield f"tcp://127.0.0.1:{common.find_free_port():d}"

    def _test_default_store_timeout(self, backend):
        for init_method in self._init_methods():
            c2p = []
            t = threading.Thread(
                target=self._test_store_timeout, args=(backend, init_method, c2p)
            )
            t.daemon = True
            t.start()
            t.join(5)

            self.assertEqual(1, len(c2p))
            if isinstance(c2p[0], float):
                # waiting time should be 1s, use 3s to rule out false alarm
                self.assertGreater(3, c2p[0])
            elif isinstance(c2p[0], RuntimeError):
                # let @retry_on_connect_failures handle the error
                raise c2p[0]
            else:
                raise RuntimeError(f"Unexpected type {type(c2p[0])}")


class TimeoutTest(TestCase):
    @retry_on_connect_failures
    def test_store_based_barrier(self):
        f = tempfile.NamedTemporaryFile(delete=False)
        port = common.find_free_port()

        def thread_work(timeout, init_type, world_size, rank, error_list):
            # we need to create a separate store just for the store barrier test
            if init_type == "file":
                barrier_store = dist.FileStore(f.name)
            elif init_type == "tcp":
                barrier_store = dist.TCPStore(
                    "localhost",
                    port,
                    world_size,
                    is_master=rank == 0,
                    wait_for_workers=False,
                )
            elif init_type == "hash":
                barrier_store = dist.HashStore()
            try:
                # 1 missing worker will cause it to timeout
                if rank != world_size - 1:
                    c10d._store_based_barrier(
                        rank=rank,
                        store=barrier_store,
                        group_name="_",
                        rendezvous_count=world_size,
                        timeout=timeout,
                        logging_interval=timeout / 2,
                    )
            except torch.distributed.DistStoreError as e:
                self.assertTrue(isinstance(e, torch.distributed.DistError))
                error_list.append(e)

        world_size = 4
        error_list = []
        threads = []
        for init_type in ["file", "tcp", "hash"]:
            for rank in range(world_size):
                t = threading.Thread(
                    target=thread_work,
                    args=(
                        timedelta(seconds=3),
                        init_type,
                        world_size,
                        rank,
                        error_list,
                    ),
                )
                threads.append(t)
                t.start()

            for thread in threads:
                thread.join()

            # we expect the world_size-1 threads to have failed
            self.assertEqual(len(error_list), world_size - 1)
            for error in error_list:
                self.assertTrue(
                    "Timed out initializing process group in store based barrier"
                    in error.args[0]
                )
            error_list = []
            threads = []


class Net(nn.Module):
    def __init__(self) -> None:
        super().__init__()
        self.fc1 = nn.Linear(2, 10, bias=False)
        self.fc2 = nn.Linear(10, 50, bias=False)
        self.fc3 = nn.Linear(50, 4, bias=False)
        self.relu = nn.ReLU()

    def forward(self, x):
        x = self.relu(self.fc1(x))
        x = self.relu(self.fc2(x))
        x = self.fc3(x)
        return F.softmax(x, dim=1)


class DoubleGpuNet(nn.Module):
    def __init__(self, gpus):
        super().__init__()
        self.fc1 = nn.Linear(2, 10, bias=False).to(gpus[0])
        self.fc2 = nn.Linear(10, 50, bias=False).to(gpus[1])
        self.fc3 = nn.Linear(50, 4, bias=False).to(gpus[1])
        self.relu = nn.ReLU()
        self.no_grad_param = nn.Parameter(
            torch.tensor([2, 2]).long(), requires_grad=False
        ).to(gpus[0])

    def forward(self, x):
        dev0 = self.fc1.weight.device
        dev1 = self.fc2.weight.device
        x = self.relu(self.fc1(x.to(dev0)))
        x = self.relu(self.fc2(x.to(dev1)))
        x = self.fc3(x)
        return F.softmax(x, dim=1).to(dev0)


class QuadraGpuNet(nn.Module):
    def __init__(self, gpus):
        super().__init__()
        self.fc1 = nn.Linear(2, 10, bias=False).to(gpus[0])
        self.fc2 = nn.Linear(10, 50, bias=False).to(gpus[1])
        self.fc3 = nn.Linear(50, 4, bias=False).to(gpus[2])
        self.fc4 = nn.Linear(4, 4, bias=False).to(gpus[3])
        self.relu = nn.ReLU()
        self.no_grad_param = nn.Parameter(
            torch.tensor([2, 2]).long(), requires_grad=False
        ).to(gpus[0])

    def forward(self, x):
        dev0 = self.fc1.weight.device
        dev1 = self.fc2.weight.device
        dev2 = self.fc3.weight.device
        dev3 = self.fc4.weight.device
        x = self.relu(self.fc1(x.to(dev0)))
        x = self.relu(self.fc2(x.to(dev1)))
        x = self.relu(self.fc3(x.to(dev2)))
        x = self.fc4(x.to(dev3))
        return F.softmax(x, dim=1).to(dev0)


class ConvNet(nn.Module):
    def __init__(self, gpus, layouts, dtypes):
        super().__init__()
        self.dtypes = dtypes
        if isinstance(gpus, list):
            self.layer_gpus = gpus
        else:
            gpus = [gpus] * 4
        self.conv0 = torch.nn.Conv2d(8, 16, (2, 2)).to(
            device=gpus[0], memory_format=layouts[0], dtype=dtypes[0]
        )
        self.conv1 = torch.nn.Conv2d(16, 32, (2, 2)).to(
            device=gpus[1], memory_format=layouts[1], dtype=dtypes[1]
        )
        self.conv2 = torch.nn.Conv2d(32, 16, (2, 2)).to(
            device=gpus[2], memory_format=layouts[2], dtype=dtypes[2]
        )
        self.conv3 = torch.nn.Conv2d(16, 8, (2, 2)).to(
            device=gpus[3], memory_format=layouts[3], dtype=dtypes[3]
        )

    def forward(self, x):
        x = x.to(self.dtypes[0])
        # Could say
        # x = self.conv0(x).to(device=self.conv1.weight.device, dtype=self.dtypes[1])
        # etc.  But I don't want to appeal to the weights' devices directly, because part of this test's purpose
        # is to verify weights are where expected if the model gets replicated.
        gpus = self.layer_gpus if hasattr(self, "layer_gpus") else [x.device] * 4
        x = self.conv0(x).to(device=gpus[1], dtype=self.dtypes[1])
        x = self.conv1(x).to(device=gpus[2], dtype=self.dtypes[2])
        x = self.conv2(x).to(device=gpus[3], dtype=self.dtypes[3])
        return self.conv3(x)


# A model involving FFTs, used to test DDP with complex tensors
class FFTModel(nn.Module):
    def __init__(self, hin, win, n_features):
        super().__init__()
        self.hin = hin
        self.win = win
        self.weight = nn.Parameter(
            torch.ones((n_features, n_features, hin, win // 2 + 1), dtype=torch.cfloat)
        )

    def forward(self, x):
        xc = torch.fft.rfft2(x, s=(self.hin, self.win), dim=(-2, -1), norm="ortho")
        xcw = torch.einsum("nchw,cohw->nohw", xc, self.weight)
        x = torch.fft.irfft2(xcw, dim=(-2, -1), norm="ortho")
        return x


class Task(nn.Module):
    def __init__(self) -> None:
        super().__init__()
        self.p = nn.Parameter(torch.ones(2, 2))

    def forward(self, x):
        return self.p + x


class ModuleForDdpCommHook(nn.Module):
    def __init__(self) -> None:
        super().__init__()
        self.t0 = Task()

    def forward(self, x, rank):
        return self.t0(x + rank)


class SparseGradientModule(nn.Module):
    def __init__(self) -> None:
        super().__init__()
        self.embedding = nn.EmbeddingBag(10, 10, sparse=True)

    def forward(self, x):
        return F.softmax(self.embedding(x), dim=1)


class CommonDistributedDataParallelTest:
    def tearDown(self):
        # DistributedDataParallel test doesn't seem to call FileStore destructor
        # TODO: investigate this test and the test is known to have issues
        # Use this hack to remove files for that test
        try:
            os.remove(self.file_name)
        except (OSError, AttributeError):
            pass

    @property
    def world_size(self):
        return 2

    def _prepare_single_device_module(
        self,
        process_group,
        devices,
        device_ids,
        global_batch_size,
        gradient_as_bucket_view=False,
    ):
        model = Net()
        device = devices[0] if devices else torch.device(f"cuda:{self.rank:d}")
        ddp_model = DistributedDataParallel(
            copy.deepcopy(model).to(device),
            device_ids=device_ids,
            process_group=process_group,
            bucket_cap_mb=0.001,
            gradient_as_bucket_view=gradient_as_bucket_view,
        )

        model.to(device)

        input = torch.randn(global_batch_size, 2).to(device)
        target = torch.randn(global_batch_size, 4).to(device)

        return model, ddp_model, input, target

    def _prepare_multi_device_module(
        self,
        process_group,
        devices,
        device_ids,
        global_batch_size,
        gradient_as_bucket_view=False,
    ):
        self.assertTrue(
            len(devices) == 2 or len(devices) == 4,
            f"unexpected devices for ddp tests {devices}",
        )
        if len(devices) == 2:
            model = DoubleGpuNet(devices)
        elif len(devices) == 4:
            model = QuadraGpuNet(devices)

        ddp_model = DistributedDataParallel(
            copy.deepcopy(model),
            device_ids=device_ids,
            process_group=process_group,
            bucket_cap_mb=0.001,
            gradient_as_bucket_view=gradient_as_bucket_view,
        )

        input = torch.randn(global_batch_size, 2).cuda(devices[0])
        target = torch.randn(global_batch_size, 4)

        return model, ddp_model, input, target

    def _get_store(self):
        return dist.FileStore(self.file_name, self.world_size)

    def _get_process_group(self):
        raise NotImplementedError("To be implemented by child class")

    def _train_model(
        self, model, input_var, target, loss, run_checkpoint=False, use_reentrant=True
    ):
        model.train()
        if run_checkpoint:
            output = checkpoint(model, input_var, use_reentrant=use_reentrant)
        else:
            output = model(input_var)
        l = loss(output, target)
        l.backward()

    def _test_ddp_checkpointing(
        self,
        input_model,
        process_group,
        use_bucket_view,
        find_unused_parameters=False,
        static_graph=False,
        run_checkpoint=False,
        use_reentrant=True,
        allow_none_grads=False,
    ):
        # to reproduce the same training results
        torch.cuda.set_device(self.rank)
        torch.manual_seed(31415)
        model = copy.deepcopy(input_model).cuda()
        ddp_model = copy.deepcopy(input_model).cuda()
        ddp_model = nn.parallel.DistributedDataParallel(
            ddp_model,
            bucket_cap_mb=1,
            gradient_as_bucket_view=use_bucket_view,
            device_ids=[self.rank],
            process_group=process_group,
            find_unused_parameters=find_unused_parameters,
            static_graph=static_graph,
        )
        self.assertEqual(
            ddp_model._get_ddp_logging_data().get("static_graph", 0), static_graph
        )
        input, ddp_input, target, ddp_target = self._prepare_dummy_data()
        loss = nn.MSELoss()
        n_iters = 5
        for i in range(n_iters):
            model.zero_grad(set_to_none=False)
            ddp_model.zero_grad(set_to_none=False)
            self._train_model(
                model,
                input,
                target,
                loss,
                run_checkpoint=run_checkpoint,
                use_reentrant=use_reentrant,
            )
            self._train_model(
                ddp_model,
                ddp_input,
                ddp_target,
                loss,
                run_checkpoint=run_checkpoint,
                use_reentrant=use_reentrant,
            )
            for i, j in zip(model.parameters(), ddp_model.parameters()):
                if not allow_none_grads:
                    self.assertTrue(i.grad is not None)
                    self.assertTrue(j.grad is not None)
                self.assertEqual(i.grad, j.grad, rtol=1.3e-06, atol=5e-5)

    # A list of tests for ddp with activation checkpointing
    # when gradient_as_bucket_view=True, False.
    # Most of the tests are referred to
    # https://github.com/facebookresearch/fairscale/blob/main/tests/nn/pipe/test_checkpoint_ddp.py
    class CheckpointOnceModule(nn.Module):
        """
        Runs checkpoint for a single layer in the model.
        """

        def __init__(self, use_reentrant=True):
            super().__init__()
            self.l1 = nn.Linear(20, 20)
            self.l2 = nn.Linear(20, 20)
            self.use_reentrant = use_reentrant

        def forward(self, inp):
            x = self.l1(inp)
            x = checkpoint(self.l2, x, use_reentrant=self.use_reentrant)
            return x

    class CheckpointTwiceModule(CheckpointOnceModule):
        """
        Runs checkpoint for the same layer twice in a model. This simulates use
        cases such as pipeline parallel where the same layer can be checkpointed
        more than one time.
        """

        def __init__(self, use_reentrant=True):
            super().__init__(use_reentrant=use_reentrant)

        def forward(self, inp):
            x = self.l1(inp)
            x = checkpoint(self.l2, x, use_reentrant=self.use_reentrant)
            x = checkpoint(self.l2, x, use_reentrant=self.use_reentrant)
            return x

    class CheckpointTwiceModuleWeightSharing(CheckpointTwiceModule):
        """
        Similar to CheckpointTwiceModule but the weights are shared.
        """

        def __init__(self, use_reentrant=True):
            super().__init__(use_reentrant=use_reentrant)
            # Share weights
            self.l1.weight = self.l2.weight

        def forward(self, inp):
            x = self.l1(inp)
            x = checkpoint(self.l2, x, use_reentrant=self.use_reentrant)
            x = checkpoint(self.l2, x, use_reentrant=self.use_reentrant)
            return x

    class DynamicCheckpointTwiceModule(CheckpointTwiceModule):
        def __init__(self, use_reentrant=True):
            super().__init__(use_reentrant=use_reentrant)
            self.count = 0

        def forward(self, inp):
            if self.count % 2:
                x = checkpoint(self.l1, inp, use_reentrant=self.use_reentrant)
            else:
                x = checkpoint(self.l2, inp, use_reentrant=self.use_reentrant)

            self.count += 1
            return x

    class DynamicCheckpointTwiceModuleWeightSharing(DynamicCheckpointTwiceModule):
        def __init__(self, use_reentrant=True):
            super().__init__(use_reentrant=use_reentrant)
            # Share weights
            self.l1.weight = self.l2.weight

    def _prepare_dummy_data(self):
        ddp_bs = 16
        bs = ddp_bs * self.world_size
        input = torch.rand((bs, 20), device="cuda", requires_grad=True)
        target = torch.randn((bs, 20), device="cuda")
        offset = self.rank * ddp_bs
        ddp_input = input[offset : offset + ddp_bs]
        ddp_target = target[offset : offset + ddp_bs]
        return input, ddp_input, target, ddp_target

    @skip_if_lt_x_gpu(2)
    @parametrize("use_reentrant", [True, False])
    def test_ddp_checkpointing_once(self, use_reentrant):
        """
        DDP works as expected when layer is checkpointed only once.
        """
        process_group = self._get_process_group()
        for use_bucket_view, static_graph in product((False, True), (False, True)):
            self._test_ddp_checkpointing(
                self.CheckpointOnceModule(use_reentrant=use_reentrant),
                process_group=process_group,
                use_bucket_view=use_bucket_view,
                static_graph=static_graph,
            )
            if static_graph:
                # find_unused_parameters does not make a difference, since it is
                # ignored for static graph.
                self._test_ddp_checkpointing(
                    self.CheckpointOnceModule(),
                    process_group=process_group,
                    use_bucket_view=use_bucket_view,
                    static_graph=static_graph,
                    find_unused_parameters=True,
                )

    @skip_if_lt_x_gpu(2)
    @parametrize("use_reentrant", [True, False])
    def test_ddp_checkpointing_unused_params(self, use_reentrant):
        """
        With reentrant autograd checkpointing impl, DDP will fail when there are
        unused params in the model and no static graph training. With
        non-reentrant checkpointing implementation, this works as expected.
        """
        process_group = self._get_process_group()
        for use_bucket_view in (True, False):
            err_ctx = (
                nullcontext()
                if not use_reentrant
                else self.assertRaisesRegex(
                    RuntimeError, "Expected to mark a variable ready only once."
                )
            )
            with err_ctx:
                self._test_ddp_checkpointing(
                    self.CheckpointOnceModule(use_reentrant=use_reentrant),
                    process_group=process_group,
                    use_bucket_view=use_bucket_view,
                    find_unused_parameters=True,
                )
            # test passes when static_graph is true
            self._test_ddp_checkpointing(
                self.CheckpointOnceModule(use_reentrant=use_reentrant),
                process_group=process_group,
                use_bucket_view=use_bucket_view,
                find_unused_parameters=True,
                static_graph=True,
            )

    @skip_if_lt_x_gpu(2)
    @parametrize("use_reentrant", [True, False])
    def test_ddp_checkpointing_twice(self, use_reentrant):
        """
        Checkpointing twice fails for non-static graph with reentrant checkpoint
        implementation, succeeds with non-reentrant checkpoint implementation.
        """
        process_group = self._get_process_group()
        for use_bucket_view in (True, False):
            err_ctx = (
                nullcontext()
                if not use_reentrant
                else self.assertRaisesRegex(
                    RuntimeError, "Expected to mark a variable ready only once."
                )
            )
            with err_ctx:
                self._test_ddp_checkpointing(
                    self.CheckpointTwiceModule(use_reentrant=use_reentrant),
                    process_group=process_group,
                    use_bucket_view=use_bucket_view,
                    static_graph=False,
                )

            with err_ctx:
                self._test_ddp_checkpointing(
                    self.CheckpointTwiceModule(use_reentrant=use_reentrant),
                    process_group=process_group,
                    use_bucket_view=use_bucket_view,
                    static_graph=False,
                    find_unused_parameters=True,
                )

    @skip_if_lt_x_gpu(2)
    @parametrize("use_reentrant", [True, False])
    def test_ddp_checkpointing_twice_static_graph(self, use_reentrant):
        """
        Regardless of reentrant or non-reentrant checkpointing impl,
        checkpointing twice works with static graph enabled.
        """
        process_group = self._get_process_group()
        for use_bucket_view in (True, False):
            # Test passes when static_graph=True.
            self._test_ddp_checkpointing(
                self.CheckpointTwiceModule(use_reentrant=use_reentrant),
                process_group=process_group,
                use_bucket_view=use_bucket_view,
                static_graph=True,
            )

    @skip_if_lt_x_gpu(2)
    def test_ddp_checkpointing_dynamic_module(self):
        """
        Dynamic module can be checkpointed, multiple times, with non-reentrant
        checkpointing implementation.
        """
        process_group = self._get_process_group()
        for use_bucket_view in (True, False):
            self._test_ddp_checkpointing(
                self.DynamicCheckpointTwiceModule(use_reentrant=False),
                process_group=process_group,
                use_bucket_view=use_bucket_view,
                static_graph=False,
                find_unused_parameters=True,
                # Grads can be none sometimes due to dynamic module not using
                # all params.
                allow_none_grads=True,
            )

    @skip_if_lt_x_gpu(2)
    def test_ddp_checkpointing_dynamic_weight_sharing(self):
        """
        Dynamic module can be checkpointed multiple times with weight sharing
        using non-reentrant checkpointing implementation.
        """
        process_group = self._get_process_group()
        for use_bucket_view in (True, False):
            self._test_ddp_checkpointing(
                self.DynamicCheckpointTwiceModuleWeightSharing(use_reentrant=False),
                process_group=process_group,
                use_bucket_view=use_bucket_view,
                static_graph=False,
                find_unused_parameters=True,
                # Grads can be none sometimes due to dynamic module not using
                # all params.
                allow_none_grads=True,
            )

    # DDP works as expected if there is weight sharing among layers
    @skip_if_lt_x_gpu(2)
    @parametrize("use_reentrant", [True, False])
    def test_ddp_checkpointing_weight_sharing(self, use_reentrant):
        """
        Test that checkpointing with weight sharing works.
        """
        process_group = self._get_process_group()
        torch.cuda.set_device(self.rank)
        for use_bucket_view, static_graph in product((False, True), (False, True)):
            torch.manual_seed(31415)
            l1 = nn.Linear(20, 20)
            l2 = nn.Linear(20, 20)
            l1.weight = l2.weight
            model = nn.Sequential(l1, l2)
            self._test_ddp_checkpointing(
                model,
                process_group=process_group,
                use_bucket_view=use_bucket_view,
                static_graph=static_graph,
                run_checkpoint=True,
                use_reentrant=use_reentrant,
            )

    @skip_if_lt_x_gpu(2)
    def test_ddp_checkpointing_twice_weight_sharing(self):
        """
        Checkpointing should work with static graph in the case of checkpointing
        same layer twice and having weights shared across layers.
        """
        process_group = self._get_process_group()
        torch.cuda.set_device(self.rank)
        for use_bucket_view in (True, False):
            self._test_ddp_checkpointing(
                self.CheckpointTwiceModuleWeightSharing(),
                process_group=process_group,
                use_bucket_view=use_bucket_view,
                static_graph=True,
            )

    def test_invalid_powerSGD_state(self):
        for start_powerSGD_iter, use_error_feedback, warm_start in product(
            [0, 1], [True, False], [True, False]
        ):
            if not use_error_feedback and not warm_start:
                continue
            with self.assertRaisesRegex(
                ValueError,
                "Expect `start_powerSGD_iter` > 1 if `use_error_feedback` or `warm_start` is enabled, "
                "because PowerSGD can only be applied after the first two iterations in DDP.",
            ):
                powerSGD.PowerSGDState(
                    process_group=None,
                    matrix_approximation_rank=1,
                    start_powerSGD_iter=start_powerSGD_iter,
                    use_error_feedback=use_error_feedback,
                    warm_start=warm_start,
                )

    def _test_ddp_with_process_group(
        self,
        process_group,
        devices,
        device_ids,
        multi_device=False,
        gradient_as_bucket_view=False,
    ):
        """
        Note: we pass down `device_ids` all the way to DistributedDataParallel
        as part of the test. Below you find tests that either use a list of
        integers, a list of `torch.Device` instances, or an empty list.
        The `devices` argument is used to control placement of the model and
        must always be specified as list of `torch.Device` instances.
        """
        local_batch_size = 1 if devices is None else len(devices)
        global_batch_size = self.world_size * local_batch_size

        if multi_device:
            model, ddp_model, input, target = self._prepare_multi_device_module(
                process_group,
                devices,
                device_ids,
                global_batch_size,
                gradient_as_bucket_view,
            )
            ddp_logging_data = ddp_model._get_ddp_logging_data()
            self.assertTrue(ddp_logging_data.get("is_multi_device_module"))
        else:
            model, ddp_model, input, target = self._prepare_single_device_module(
                process_group,
                devices,
                device_ids,
                global_batch_size,
                gradient_as_bucket_view,
            )
            ddp_logging_data = ddp_model._get_ddp_logging_data()
            self.assertFalse(ddp_logging_data.get("is_multi_device_module"))

        def step_model(model, input, target):
            model.train()
            output = model(input)
            loss = F.mse_loss(output, target.to(output.device))
            loss.backward()

        def update_parameters(model):
            for param in model.parameters():
                with torch.no_grad():
                    param -= param.grad
                param.grad = None

        # check two model parameters over 2 iterations
        for iteration in range(2):
            # single cpu/gpu training
            step_model(model, input, target)

            # DDP training, DDP scatters subsets of input_cpu to nodes/GPUs
            step_model(
                ddp_model,
                input[
                    self.rank * local_batch_size : (self.rank + 1) * local_batch_size
                ],
                target[
                    self.rank * local_batch_size : (self.rank + 1) * local_batch_size
                ],
            )

            # Update weights and run a second iteration to shake out errors
            update_parameters(model)
            update_parameters(ddp_model)
            self.assertEqual(
                len(list(model.parameters())), len(list(ddp_model.parameters()))
            )
            for i, j in zip(model.parameters(), ddp_model.parameters()):
                self.assertEqual(i, j, rtol=1.3e-06, atol=5e-5)

            # Shuffle the input so that DDP input is different
            torch.manual_seed(1337 + iteration)
            input = input[torch.randperm(global_batch_size)]

    def _gpu_model_with_ddp_comm_hook(
        self, process_group, hook=None, gradient_as_bucket_view=False, state=None
    ):
        device_id = gpus_for_rank(self.world_size)[self.rank][0]
        gpu_model = DistributedDataParallel(
            ModuleForDdpCommHook().to(device_id),
            device_ids=[device_id],
            process_group=process_group,
            gradient_as_bucket_view=gradient_as_bucket_view,
        )

        # Register a DDP communication hook if any.
        if hook is not None:
            gpu_model.register_comm_hook(state, hook)

        return gpu_model

    def _gpu_model_with_builtin_ddp_comm_hook(
        self, process_group, hook=None, gradient_as_bucket_view=False
    ):
        device_id = gpus_for_rank(self.world_size)[self.rank][0]
        gpu_model = DistributedDataParallel(
            ModuleForDdpCommHook().to(device_id),
            device_ids=[device_id],
            process_group=process_group,
            gradient_as_bucket_view=gradient_as_bucket_view,
        )

        # Register a built-in DDP communication hook if defined
        if hook is not None:
            gpu_model._register_builtin_comm_hook(hook)

        return gpu_model

    def _run_and_verify_hook(self, model, input, expected_grad):
        # Run forward
        output = model(input, self.rank)

        # Run backward
        output.mean().backward()

        [self.assertEqual(p.grad, expected_grad) for p in model.parameters()]

    def _simple_hook(
        self, state: object, bucket: dist.GradBucket
    ) -> torch.futures.Future[torch.Tensor]:
        fut = torch.futures.Future()
        fut.set_result(torch.ones_like(bucket.buffer()))

        def fut_then(fut):
            # Add ones to fut's result.
            t = fut.value()
            return t + torch.ones_like(t)

        return fut.then(fut_then)

    def _test_not_nan(self, model, x):
        y = model(x)
        self.assertFalse(y.isnan().any().item())
        y.sum().backward()
        for p in model.parameters():
            self.assertFalse(p.grad.isnan().any().item())

    @skip_if_lt_x_gpu(2)
    def test_sync_batch_norm_only_empty_input(self):
        pg = self._get_process_group()

        model = torch.nn.Sequential(
            nn.BatchNorm2d(2),
        ).to(device=self.rank)
        model = DistributedDataParallel(
            model,
            device_ids=[self.rank],
            process_group=pg,
        )
        model = nn.SyncBatchNorm.convert_sync_batchnorm(
            model,
            process_group=pg,
        )

        model.train()

        # only rank 0 receives empty inputs
        x = torch.zeros(
            (1 if self.rank != 0 else 0, 2, 11, 13),
            dtype=torch.float32,
            device=self.rank,
        )

        # input requires grad, this will trigger the collective communication
        # in the backward pass
        x.requires_grad = True
        self._test_not_nan(model, x)

        # input does not requires grad
        x.requires_grad = False
        self._test_not_nan(model, x)

        # all ranks receive empty inputs
        x = torch.zeros((0, 2, 11, 13), dtype=torch.float32, device=self.rank)

        # input requires grad, this will trigger the collective communication
        # in the backward pass
        x.requires_grad = True
        self._test_not_nan(model, x)

        # input does not requires grad
        x.requires_grad = False
        self._test_not_nan(model, x)

    @skip_if_lt_x_gpu(2)
    def test_sync_batch_norm_empty_input(self):
        pg = self._get_process_group()

        model = torch.nn.Sequential(
            nn.Conv2d(2, 2, 3),
            nn.BatchNorm2d(2),
            nn.Linear(28, 2),
        ).to(device=self.rank)
        model = DistributedDataParallel(
            model,
            device_ids=[self.rank],
            process_group=pg,
        )
        model = nn.SyncBatchNorm.convert_sync_batchnorm(
            model,
            process_group=pg,
        )

        model.train()
        # only rank 0 receives empty inputs
        x = torch.zeros(
            (3 if self.rank != 0 else 0, 2, 30, 30),
            dtype=torch.float32,
            device=self.rank,
        )

        self._test_not_nan(model, x)

        # all ranks receive empty inputs
        x = torch.zeros((0, 2, 30, 30), dtype=torch.float32, device=self.rank)

        self._test_not_nan(model, x)

    @dataclass
    class CustomOutput:
        o1: Optional[torch.Tensor]
        o2: dict[str, torch.Tensor]

    class DataclassOutputModule(nn.Module):
        def __init__(self, skip_o1):
            super().__init__()
            self.seq1 = nn.Sequential(*[nn.Linear(10, 10) for _ in range(3)])
            self.relu = nn.ReLU()
            self.seq2 = nn.Sequential(*[nn.Linear(10, 10) for _ in range(3)])
            self.skip_o1 = skip_o1

        def forward(self, x):
            o1 = None if self.skip_o1 else self.relu(self.seq1(x))
            o2 = {"a": self.seq2(x), "b": self.relu(self.seq2(x))}
            return CommonDistributedDataParallelTest.CustomOutput(o1=o1, o2=o2)

    def _test_dataclass_output(self, skip_o1):
        net_x = torch.cat([torch.ones(4, 10) * i for i in range(self.world_size)]).to(
            self.rank
        )
        ddp_x = torch.ones(4, 10, device=self.rank) * self.rank

        # use manual_seed to make sure local models start with the same values
        torch.manual_seed(0)
        net = self.DataclassOutputModule(skip_o1=skip_o1).to(self.rank)
        ddp = DistributedDataParallel(
            copy.deepcopy(net),
            device_ids=[self.rank],
            find_unused_parameters=True,
            static_graph=False,
            process_group=self._get_process_group(),
        )

        net_out = net(net_x)
        ddp_out = ddp(ddp_x)

        net_loss = F.mse_loss(
            (
                net_out.o1 + net_out.o2["a"] + net_out.o2["b"]
                if not skip_o1
                else net_out.o2["a"] + net_out.o2["b"]
            ),
            torch.ones_like(net_out.o2["a"], device=self.rank),
        )
        ddp_loss = F.mse_loss(
            (
                ddp_out.o1 + ddp_out.o2["a"] + ddp_out.o2["b"]
                if not skip_o1
                else ddp_out.o2["a"] + ddp_out.o2["b"]
            ),
            torch.ones_like(ddp_out.o2["a"], device=self.rank),
        )

        net_loss.backward()
        ddp_loss.backward()

        for p1, p2 in zip(net.parameters(), ddp.parameters()):
            if torch.is_tensor(p1.grad):
                self.assertTrue(p1.grad.allclose(p2.grad))
            else:
                self.assertEqual(p1.grad, p2.grad)

    @skip_if_lt_x_gpu(2)
    def test_dataclass_output(self):
        self._test_dataclass_output(skip_o1=False)

    @skip_if_lt_x_gpu(2)
    def test_dataclass_output_unused_param(self):
        self._test_dataclass_output(skip_o1=True)


class ComputeBucketAssignmentTest(TestCase):
    def test_single_limit_single_dtype(self):
        tensors = [
            torch.empty([100], dtype=torch.float),
            torch.empty([200], dtype=torch.float),
            torch.empty([100], dtype=torch.float),
            torch.empty([50], dtype=torch.float),
        ]
        result, per_bucket_size_limits = dist._compute_bucket_assignment_by_size(
            tensors, [400]
        )
        self.assertTrue(all(size_lim == 400 for size_lim in per_bucket_size_limits))
        self.assertEqual([[0], [1], [2], [3]], result)

    def test_single_limit_multi_dtype(self):
        tensors = [
            torch.empty([50], dtype=torch.float),
            torch.empty([25], dtype=torch.double),
            torch.empty([50], dtype=torch.float),
            torch.empty([25], dtype=torch.double),
            torch.empty([50], dtype=torch.float),
            torch.empty([25], dtype=torch.double),
        ]
        result, per_bucket_size_limits = dist._compute_bucket_assignment_by_size(
            tensors, [400]
        )
        self.assertTrue(all(size_lim == 400 for size_lim in per_bucket_size_limits))
        self.assertEqual([[0, 2], [1, 3], [4], [5]], result)

    def test_multi_limit_single_dtype(self):
        tensors = [
            torch.empty([10], dtype=torch.float),
            torch.empty([10], dtype=torch.float),
            torch.empty([10], dtype=torch.float),
            torch.empty([10], dtype=torch.float),
        ]
        result, per_bucket_size_limits = dist._compute_bucket_assignment_by_size(
            tensors, [40, 80]
        )
        self.assertEqual(per_bucket_size_limits, [40, 80, 80])
        self.assertEqual([[0], [1, 2], [3]], result)

    def test_multi_limit_multi_dtype(self):
        tensors = [
            torch.empty([50], dtype=torch.float),
            torch.empty([25], dtype=torch.double),
            torch.empty([50], dtype=torch.float),
            torch.empty([25], dtype=torch.double),
            torch.empty([50], dtype=torch.float),
            torch.empty([25], dtype=torch.double),
        ]
        result, per_bucket_size_limits = dist._compute_bucket_assignment_by_size(
            tensors, [200, 400]
        )
        self.assertEqual([[0], [1], [2, 4], [3, 5]], result)
        self.assertEqual(per_bucket_size_limits, [200, 200, 400, 400])


class AbstractCommTest:
    @property
    def op_timeout_sec(self):
        return 1

    @property
    def world_size(self):
        return 2

    @property
    def device(self):
        self.fail("test subclass didn't override device")

    def _verify_sequence_number_across_pg(self, pg, verify_pg):
        seq_num = pg._get_sequence_number_for_group()
        obj_list = [None for _ in range(dist.get_world_size(verify_pg))]
        # We use a separate pg to verify the sequence numbers, otherwise these
        # collectives will themselves increment the sequence number.
        dist.all_gather_object(obj_list, seq_num, group=verify_pg)
        self.assertEqual(len(set(obj_list)), 1)
        return obj_list[0]

    def _test_sequence_num_incremented(self, process_group, ranks):
        # verify initial sequence numbers. Use a distinct process group for
        # verification to keep counts as expected with respect to process_group.
        verify_pg = dist.new_group(
            ranks=ranks,
            backend="gloo",
        )
        assert dist.get_world_size(process_group) == dist.get_world_size(verify_pg)

        initial_num = (
            self._verify_sequence_number_across_pg(
                pg=process_group, verify_pg=verify_pg
            )
            if not c10d._rank_not_in_group(process_group)
            else -1
        )

        # Verify sequence numbers are appropriately incremented
        for i in range(10):
            t = torch.ones(1, device=torch.cuda.current_device())
            dist.all_reduce(t, group=process_group)
            if not c10d._rank_not_in_group(process_group):
                seq_num = self._verify_sequence_number_across_pg(
                    pg=process_group,
                    verify_pg=verify_pg,
                )
                self.assertEqual(initial_num + i + 1, seq_num)

        if dist.get_world_size(process_group) > 2:
            # Test when certain ranks don't call collectives
            if dist.get_rank(process_group) not in [0, 2]:
                dist.all_reduce(t, group=process_group, async_op=True)
            # Now ranks 0 and 2 should be lagging by 1.
            if not c10d._rank_not_in_group(process_group):
                seq_num = process_group._get_sequence_number_for_group()
                rank = dist.get_rank(process_group)
                obj_list = [None for _ in range(dist.get_world_size(verify_pg))]
                dist.all_gather_object(obj_list, (rank, seq_num), group=verify_pg)
                rank_to_seq_num = dict(obj_list)
                self.assertEqual(len(set(rank_to_seq_num.values())), 2)
                self.assertEqual(rank_to_seq_num[0], rank_to_seq_num[2])
                expected_same = {
                    rank_to_seq_num[i]
                    for i in rank_to_seq_num.keys()
                    if i not in [0, 2]
                }
                self.assertEqual(len(expected_same), 1)
                self.assertEqual(rank_to_seq_num[0] + 1, rank_to_seq_num[1])

    def _test_sequence_num_incremented_default_group(self, backend_name):
        torch.cuda.set_device(self.rank)
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend_name,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        self._test_sequence_num_incremented(
            c10d._get_default_group(),
            ranks=list(range(dist.get_world_size())),
        )

    def _test_sequence_num_incremented_subgroup(self, backend_name):
        torch.cuda.set_device(self.rank)
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend_name,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        subgroup_ranks = [0, 1, 2]
        subgroup = dist.new_group(subgroup_ranks)
        self._test_sequence_num_incremented(subgroup, subgroup_ranks)

    def _test_sequence_num_set_default_pg(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )

        default_pg = c10d._get_default_group()
        seq_num = default_pg._get_sequence_number_for_group()
        obj_list = [None for _ in range(dist.get_world_size())]
        dist.all_gather_object(obj_list, seq_num)
        self.assertEqual(len(set(obj_list)), 1)

    def _test_sequence_num_set_new_group(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )

        subgroup = dist.new_group([0, 1])

        if not c10d._rank_not_in_group(subgroup):
            subgroup_seq = subgroup._get_sequence_number_for_group()
            obj_list = [None for _ in range(dist.get_world_size(subgroup))]
            dist.all_gather_object(obj_list, subgroup_seq, group=subgroup)
            self.assertEqual(len(set(obj_list)), 1)

    def _test_warn_not_in_group(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        in_group_ranks = list(filter(lambda x: x % 2 == 0, range(self.world_size)))
        group = dist.new_group(in_group_ranks)

        x = torch.zeros(2, 2).cuda(self.rank)
        xs = [torch.zeros(2, 2).cuda(self.rank) for _ in range(len(in_group_ranks))]
        if self.rank not in in_group_ranks:
            msg = ".*{}.*does not belong to.*"
            with self.assertWarnsOnceRegex(UserWarning, msg.format("all_gather")):
                dist.all_gather(xs, x, group=group)
            with self.assertWarnsOnceRegex(UserWarning, msg.format("all_reduce")):
                dist.all_reduce(x, group=group)
            with self.assertWarnsOnceRegex(UserWarning, msg.format("barrier")):
                dist.barrier(group=group)
            with self.assertWarnsOnceRegex(UserWarning, msg.format("broadcast")):
                dist.broadcast(x, src=0, group=group)
        else:
            dist.all_gather(xs, x, group=group)
            dist.all_reduce(x, group=group)
            dist.barrier(group=group)
            dist.broadcast(x, src=0, group=group)

    def _test_rank_membership(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        self.assertTrue(self.world_size > 1)

        group = dist.new_group(ranks=[1])
        self.assertEqual(dist.get_group_rank(group, 1), 0)
        with self.assertRaisesRegex(ValueError, "not part of group"):
            dist.get_group_rank(group, 0)
        with self.assertRaisesRegex(ValueError, "not registered"):
            dist.get_group_rank(DummyProcessGroup(self.rank, self.world_size), 0)

        self.assertEqual(dist.get_global_rank(group, 0), 1)
        with self.assertRaisesRegex(ValueError, "not part of group"):
            dist.get_global_rank(group, 1)
        with self.assertRaisesRegex(ValueError, "not registered"):
            dist.get_global_rank(DummyProcessGroup(self.rank, self.world_size), 0)

        self.assertEqual(dist.get_process_group_ranks(group), [1])

    def _test_tensor_dtype_mismatch(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )

        tensor = torch.ones(2, 2, device=self.device) * 7
        tensor_h = tensor.half()
        tensor_list = [
            torch.zeros(2, 2, device=self.device) for _ in range(self.world_size)
        ]
        tensor_list_h = list(tensor_list)
        tensor_list_h[1] = tensor_list_h[1].half()

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.all_gather(tensor_list_h, tensor)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.all_gather(tensor_list, tensor_h)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.all_gather_coalesced([tensor_list_h], tensor_list)
            dist.all_gather_coalesced([tensor_list], tensor_list_h)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.all_reduce_coalesced(tensor_list_h)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.reduce_scatter(tensor, tensor_list_h)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.reduce_scatter(tensor_h, tensor_list)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.all_to_all_single(tensor_h, tensor)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.all_to_all(tensor_list_h, tensor_list)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.all_to_all(tensor_list, tensor_list_h)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.scatter(tensor, tensor_list_h)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.gather(tensor_h, tensor_list)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.gather(tensor, tensor_list_h)

        with self.assertRaisesRegex(ValueError, "tensors with different dtypes"):
            dist.scatter(tensor_h, tensor_list)

    def _test_tensor_dtype_complex(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )

        tensor = torch.rand(2, device=self.device)
        tensor_c = torch.view_as_complex(tensor)
        tensor_list = [
            torch.rand(2, device=self.device) for _ in range(self.world_size)
        ]
        tensor_list_c = list(tensor_list)
        tensor_list_c[1] = torch.view_as_complex(tensor_list_c[1])

        dist.all_gather(tensor_list, tensor)
        dist.all_gather(tensor_list, tensor_c)
        dist.all_gather(tensor_list_c, tensor)
        dist.all_gather(tensor_list_c, tensor_c)

    def _test_bool_tensors(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        device = "cuda" if backend == "nccl" else "cpu"
        # test alltoall_base
        tensor = torch.tensor([1, 0, 0, 1], dtype=torch.bool, device=device)
        zeros = torch.tensor([0, 0, 0, 0], dtype=torch.bool, device=device)
        outensor = zeros if self.rank > 0 else tensor
        dist.broadcast(outensor, src=0)
        self.assertEqual(outensor, tensor)


# Variant of AbstractCommTest that expects world size of 4
class AbstractLargeCommTest:
    @property
    def op_timeout_sec(self):
        return 1

    @property
    def world_size(self):
        return 4

    @property
    def device(self):
        raise RuntimeError("Implement me")

    def _test_new_group_local_sync(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        rank = dist.get_rank()
        ranks_in = [rank, (rank + 2) % self.world_size]
        ranks_out = [i for i in range(self.world_size) if i not in ranks_in]
        self.assertIn(rank, ranks_in)
        self.assertNotIn(rank, ranks_out)

        self.assertIsNone(
            dist.new_group(ranks=ranks_out, use_local_synchronization=True)
        )

        new_pg = dist.new_group(ranks=ranks_in, use_local_synchronization=True)
        self.assertIsInstance(new_pg, dist.ProcessGroup)

        # PTD sorts ranks before creating the PG, so [3, 1] actually gets assigned ranks [1, 0]
        ranks_in.sort()
        self.assertEqual(dist.get_group_rank(new_pg, rank), ranks_in.index(rank))
        self.assertEqual(
            ranks_in,
            dist.get_process_group_ranks(new_pg),
            f"expecting {ranks_in} but got {dist.get_process_group_ranks(new_pg)}",
        )

    def _test_new_group_local_sync_sanity_check(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        rank = dist.get_rank()

        # split the world in 2 PGs
        rank = dist.get_rank()
        pg_idx = rank // 2
        ranks_in = [pg_idx * 2, pg_idx * 2 + 1]
        new_pg = dist.new_group(ranks=ranks_in, use_local_synchronization=True)

        input_tensor = torch.tensor([pg_idx, rank], device=self.device)
        output_tensor_list = [
            torch.tensor(
                [-1, -1],
                device=self.device,
            )
            for _ in range(new_pg.size())
        ]
        dist.all_gather(output_tensor_list, input_tensor, group=new_pg)

        expected = [
            torch.tensor([pg_idx, ranks_in[0]], device=self.device),
            torch.tensor([pg_idx, ranks_in[1]], device=self.device),
        ]
        self.assertEqual(output_tensor_list, expected)

    def _test_new_group_local_sync_duplicate_pg(self, backend):
        """
        We should support users create multiple PGs with the same set of
        members, and no conflict in group name
        """
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        rank = dist.get_rank()

        # split the world in 2 PGs
        rank = dist.get_rank()
        pg_idx = rank // 2
        ranks_in = [pg_idx * 2, pg_idx * 2 + 1]
        new_pgs = []
        for _ in range(2):
            new_pgs.append(
                dist.new_group(ranks=ranks_in, use_local_synchronization=True)
            )

        input_tensor = torch.tensor([pg_idx, rank], device=self.device)
        for new_pg in new_pgs:
            output_tensor_list = [
                torch.tensor(
                    [-1, -1],
                    device=self.device,
                )
                for _ in range(new_pg.size())
            ]
            dist.all_gather(output_tensor_list, input_tensor, group=new_pg)

            expected = [
                torch.tensor([pg_idx, ranks_in[0]], device=self.device),
                torch.tensor([pg_idx, ranks_in[1]], device=self.device),
            ]
            self.assertEqual(output_tensor_list, expected)


class CommTest(AbstractCommTest, MultiProcessTestCase):
    def setUp(self):
        super().setUp()
        self._spawn_processes()

    def tearDown(self):
        super().tearDown()
        try:
            os.remove(self.file_name)
        except OSError:
            pass

    def test_debug_level(self):
        try:
            del os.environ["TORCH_DISTRIBUTED_DEBUG"]
        except KeyError:
            pass

        dist.set_debug_level_from_env()
        # Default should be off
        default_debug_mode = dist.get_debug_level()
        self.assertEqual(default_debug_mode, dist.DebugLevel.OFF)
        mapping = {
            "OFF": dist.DebugLevel.OFF,
            "off": dist.DebugLevel.OFF,
            "oFf": dist.DebugLevel.OFF,
            "INFO": dist.DebugLevel.INFO,
            "info": dist.DebugLevel.INFO,
            "INfO": dist.DebugLevel.INFO,
            "DETAIL": dist.DebugLevel.DETAIL,
            "detail": dist.DebugLevel.DETAIL,
            "DeTaIl": dist.DebugLevel.DETAIL,
        }
        invalid_debug_modes = ["foo", 0, 1, -1]

        for mode in mapping.keys():
            os.environ["TORCH_DISTRIBUTED_DEBUG"] = str(mode)
            dist.set_debug_level_from_env()
            set_debug_mode = dist.get_debug_level()
            self.assertEqual(
                set_debug_mode,
                mapping[mode],
                f"Expected {mode} to map to {mapping[mode]} but got {set_debug_mode}",
            )

        for mode in invalid_debug_modes:
            os.environ["TORCH_DISTRIBUTED_DEBUG"] = str(mode)
            with self.assertRaisesRegex(
                ValueError, "The value of TORCH_DISTRIBUTED_DEBUG must"
            ):
                dist.set_debug_level_from_env()


class DummyWork(dist._Work):
    def wait(self, timeout=5.0):
        if torch.cuda.is_available():
            torch.cuda.current_stream().synchronize()
        return True


class DummyProcessGroup(dist.ProcessGroup):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self._bound_device_id = None
        self.global_rank = args[0]
        self.group_size = args[1]
        self._aborted = False
        self._shutdown = False

    def rank(self):
        return self.global_rank

    def size(self):
        return self.group_size

    @property
    def supports_splitting(self):
        return True

    @property
    def bound_device_id(self):
        return self._bound_device_id

    @bound_device_id.setter
    def bound_device_id(self, device):
        self._bound_device_id = device

    def eager_connect_single_device(self, device=None):
        self._bound_device_id = device

    def _set_sequence_number_for_group(self):
        pass

    def _get_backend(self, device):
        return self

    def comm_split_count(self):
        return 0

    def perform_nocolor_split(self, device):
        pass

    def getBackendName(self):
        return "Dummy"

    def allgather(self, output_tensor_lists, input_tensor_list, opts=None):
        for output_tensor_list, input_tensor in zip(
            output_tensor_lists, input_tensor_list
        ):
            for output_tensor in output_tensor_list:
                output_tensor.copy_(input_tensor)

        return DummyWork()

    def allreduce(self, tensor_list, opts=None):
        for tensor in tensor_list:
            tensor.add_(2)

        return DummyWork()

    def barrier(self, opts=None):
        store = c10d._get_default_store()
        key = "TEST:DummyProcessGroup:barrier"
        if self.rank() == 0:
            worker_count = 0
            # By default, TCPServer lives on rank 0. So rank 0 needs to make
            # sure that it does not exit too early before other ranks finish
            # using the store.
            # Note that, _store_based_barrier does not solve this problem, as
            # all ranks need to run at least one store.add(key, 0) before
            # exiting, but there is no guarantee that rank 0 is still alive at
            # that point.
            while worker_count < self.size() - 1:
                worker_count = store.add(key, 0)
        else:
            store.add(key, 1)

        return DummyWork()

    def broadcast(self, tensor_list, opts=None):
        for tensor in tensor_list:
            tensor.add_(1)

        return DummyWork()

    def reduce_scatter(self, output_tensor_list, input_tensor_lists, opts=None):
        for output_tensor, input_tensor_list in zip(
            output_tensor_list, input_tensor_lists
        ):
            output_tensor.copy_(input_tensor_list[self.rank()])

        return DummyWork()

    def send(self, tensor_list, dst, tag=0):
        for tensor in tensor_list:
            tensor.add_(1)

        return DummyWork()

    def recv(self, tensor_list, src, tag=0):
        for tensor in tensor_list:
            tensor.add_(2)

        return DummyWork()

    def abort(self) -> None:
        self._aborted = True

    def shutdown(self) -> None:
        self._shutdown = True


class PythonProcessGroupExtensionTest(MultiProcessTestCase):
    def setUp(self):
        super().setUp()
        self._spawn_processes()

    def tearDown(self):
        super().tearDown()
        try:
            os.remove(self.file_name)
        except OSError:
            pass

    def test_get_backend_name(self):
        dpg = DummyProcessGroup(0, 1)
        self.assertEqual("Dummy", dpg.name())

        # dist.Backend.register_backend(
        #     "dummy", PythonProcessGroupExtensionTest.create_dummy
        # )

        # # os.environ["MASTER_ADDR"] = "localhost"
        # # os.environ["MASTER_PORT"] = "6789"
        # # dist.init_process_group(
        # #     "cpu:dummy", rank=0, world_size=1,
        # # )
        # dpg = DummyProcessGroup(0, 1)
        # from torch.distributed.distributed_c10d import _canonicalize_group_rank
        # self.assertEqual(123, _canonicalize_group_rank(dpg, group_rank=123, return_global=False))
        # with self.assertRaises(RuntimeError):
        # _canonicalize_group_rank(dpg, group_rank=123, return_global=True)

    def test_canonicalize_helper(self):
        dist.Backend.register_backend(
            "dummy", PythonProcessGroupExtensionTest.create_dummy
        )

        os.environ["MASTER_ADDR"] = "localhost"
        os.environ["MASTER_PORT"] = "6789"
        dist.init_process_group("dummy", rank=self.rank, world_size=self.world_size)

        dpg = DummyProcessGroup(0, 124)
        from torch.distributed.distributed_c10d import _canonicalize_group_rank

        # we ensure that a process group with more ranks than the 'default' group can still be used.
        # e.g. if the dpg had 124 ranks and the world had only 2 ranks.
        self.assertEqual(
            123, _canonicalize_group_rank(dpg, group_rank=123, return_global=False)
        )
        self.assertEqual(
            0, _canonicalize_group_rank(dpg, global_rank=0, return_global=True)
        )
        with self.assertRaises(ValueError):
            # TODO(whc) this is actually catching the wrong error:
            # ValueError: Group <__mp_main__.DummyProcessGroup object at 0x7faa0a844540> is not registered,
            # please create group with torch.distributed.new_group API
            # It should be catching a different error where the rank doesn't exist in the global mapping.
            # But it's still testing the same part of the _canonicalize_group_rank helper so maybe this is fine
            _canonicalize_group_rank(dpg, group_rank=123, return_global=True)

        dist.destroy_process_group()

    def test_backend_class_attr(self):
        dist.Backend.register_backend(
            "dummy", PythonProcessGroupExtensionTest.create_dummy
        )
        self.assertEqual(dist.Backend.DUMMY, "dummy")
        self.assertEqual(
            dist.Backend._plugins["DUMMY"].creator_fn,
            PythonProcessGroupExtensionTest.create_dummy,
        )

    def test_is_backend_available(self):
        self.assertEqual(dist.is_ucc_available(), dist.is_backend_available("ucc"))
        self.assertFalse(dist.is_backend_available("dummy"))
        dist.Backend.register_backend(
            "dummy", PythonProcessGroupExtensionTest.create_dummy
        )
        self.assertTrue(dist.is_backend_available("dummy"))

    def test_backend_config(self):
        dist.Backend.register_backend(
            "dummy", PythonProcessGroupExtensionTest.create_dummy
        )

        # Ensure backend config can be created with the following arguments
        backend_config_strings_and_expected_values = [
            (dist.Backend.GLOO, "cpu:gloo,cuda:gloo"),
            (dist.Backend.NCCL, "cuda:nccl"),
            (dist.Backend.MPI, "cpu:mpi,cuda:mpi"),
            (dist.Backend.UCC, "cpu:ucc,cuda:ucc"),
            (dist.Backend.DUMMY, "cpu:dummy,cuda:dummy"),
            ("DUMMY", "cpu:dummy,cuda:dummy"),
            ("dummy", "cpu:dummy,cuda:dummy"),
            ("cpu:dummy,cuda:dummy", "cpu:dummy,cuda:dummy"),
            ("cpu:dummy,cuda:nccl", "cpu:dummy,cuda:nccl"),
            ("cpu:gloo,cuda:dummy", "cpu:gloo,cuda:dummy"),
            ("cpu:gloo,cuda:nccl", "cpu:gloo,cuda:nccl"),
        ]

        for config_str, expected_value in backend_config_strings_and_expected_values:
            with self.subTest(config_str):
                # ensures these configs strings are valid and no ValueError is raised
                config = dist.BackendConfig(config_str)
                self.assertEqual(str(config), expected_value)

        # Ensure backend config will raise ValueError with the following arguments
        invalid_backend_config_strings = [
            "cpu:gloo,cuda:nccl,",  # trailing comma
            "cpu:gloo,cuda:nccl,cpu:dummy",  # duplicate device
        ]
        for config_str in invalid_backend_config_strings:
            with self.subTest(config_str):
                with self.assertRaises(ValueError):
                    dist.BackendConfig(config_str)

    def test_init_process_group_with_multiple_backends(self):
        dist.Backend.register_backend(
            "dummy", PythonProcessGroupExtensionTest.create_dummy
        )

        os.environ["MASTER_ADDR"] = "localhost"
        os.environ["MASTER_PORT"] = "6789"
        dist.init_process_group(
            "cpu:dummy,cuda:dummy", rank=self.rank, world_size=self.world_size
        )

        # test all_gather
        input_tensor = torch.ones(2, 2) * 7
        output_tensor_list = [torch.zeros(2, 2) for _ in range(self.world_size)]
        dist.all_gather(output_tensor_list, input_tensor)

        dist.barrier()
        dist.destroy_process_group()

    class Options:
        group_name = None
        split_from = None
        split_color = None
        global_ranks_in_group = None

        def __init__(self) -> None:
            pass

        def create(self):
            pass

    @staticmethod
    def create_dummy(store, group_rank, group_size, timeout):
        return DummyProcessGroup(group_rank, group_size)

    @staticmethod
    def create_dummy_ext(dist_opts, pg_options=None):
        return DummyProcessGroup(dist_opts.group_rank, dist_opts.group_size)

    def test_collectives(self):
        dist.Backend.register_backend(
            "dummy", PythonProcessGroupExtensionTest.create_dummy
        )

        os.environ["MASTER_ADDR"] = "localhost"
        os.environ["MASTER_PORT"] = "6789"
        dist.init_process_group("dummy", rank=self.rank, world_size=self.world_size)

        # test all_gather
        input_tensor = torch.ones(2, 2) * 7
        output_tensor_list = [torch.zeros(2, 2) for _ in range(self.world_size)]
        dist.all_gather(output_tensor_list, input_tensor)

        for tensor in output_tensor_list:
            self.assertEqual(tensor, input_tensor)

        # test all_reduce
        input_tensor = torch.ones(2, 2) * 7
        dist.all_reduce(input_tensor)
        self.assertEqual(input_tensor, torch.ones(2, 2) * 7 + 2)

        # test broadcast
        input_tensor = torch.zeros(2, 2)
        dist.broadcast(input_tensor, 0, async_op=True).wait()
        self.assertEqual(torch.ones(2, 2), input_tensor)

        # test reduce_scatter
        output_tensor = torch.zeros(2, 2)
        input_tensor_list = [torch.ones(2, 2) for _ in range(self.world_size)]
        dist.reduce_scatter(output_tensor, input_tensor_list)
        self.assertEqual(output_tensor, torch.zeros(2, 2) + 1)

        dist.barrier()
        dist.destroy_process_group()

    def test_send_recv(self):
        dist.Backend.register_backend(
            "dummy", PythonProcessGroupExtensionTest.create_dummy
        )

        os.environ["MASTER_ADDR"] = "localhost"
        os.environ["MASTER_PORT"] = "6789"
        dist.init_process_group("dummy", rank=self.rank, world_size=self.world_size)

        # test send
        input_tensor = torch.zeros(2, 2)
        dist.send(input_tensor, (self.rank + 1) % self.world_size)
        self.assertEqual(input_tensor, torch.zeros(2, 2) + 1)

        with self.assertRaises(ValueError):
            dist.send(input_tensor, dist.get_rank())
        with self.assertRaises(ValueError):
            dist.send(input_tensor, group_dst=dist.get_rank())

        with self.assertRaises(ValueError):
            dist.send(input_tensor, dist.get_rank(), group_dst=dist.get_rank())
        with self.assertRaises(ValueError):
            dist.send(input_tensor)

        # test recv
        input_tensor = torch.zeros(2, 2)
        dist.recv(input_tensor, (self.rank + 1) % self.world_size)
        self.assertEqual(input_tensor, torch.zeros(2, 2) + 2)
        with self.assertRaises(ValueError):
            dist.recv(input_tensor, src=0, group_src=0)

        dist.barrier()
        # intentionally not calling into `destroy_process_group` as not all
        # user applications would explicitly that.

    def test_shutdown(self) -> None:
        dist.Backend.register_backend(
            "dummy", PythonProcessGroupExtensionTest.create_dummy
        )

        os.environ["MASTER_ADDR"] = "localhost"
        os.environ["MASTER_PORT"] = "6789"
        dist.init_process_group("dummy", rank=self.rank, world_size=self.world_size)

        pg = c10d._get_default_group()

        dist.destroy_process_group()

        self.assertTrue(pg._shutdown)

    def test_abort(self) -> None:
        dist.Backend.register_backend(
            "dummy", PythonProcessGroupExtensionTest.create_dummy
        )

        os.environ["MASTER_ADDR"] = "localhost"
        os.environ["MASTER_PORT"] = "6789"
        dist.init_process_group("dummy", rank=self.rank, world_size=self.world_size)

        pg = c10d._get_default_group()

        c10d._abort_process_group()

        self.assertTrue(pg._aborted)


instantiate_parametrized_tests(CommonDistributedDataParallelTest)


class ProcessGroupWithDispatchedCollectivesTests(MultiProcessTestCase):
    @property
    def world_size(self):
        return 1

    def setUp(self):
        super().setUp()
        self._spawn_processes()

    def tearDown(self):
        super().tearDown()
        try:
            os.remove(self.file_name)
        except OSError:
            pass

    def test_init_process_group_optional_backend(self):
        store = dist.FileStore(self.file_name, self.world_size)
        # creates both gloo and nccl backend
        if dist.is_gloo_available() and dist.is_nccl_available():
            dist.init_process_group(
                store=store,
                rank=self.rank,
                world_size=self.world_size,
            )
            dist.destroy_process_group()

    def test_init_process_group_for_all_backends(self):
        for backend in dist.Backend.backend_list:
            excepted_backend = backend
            # skip if the backend is not available on the system
            if backend == dist.Backend.UNDEFINED:
                continue
            elif backend == dist.Backend.MPI:
                if not dist.is_mpi_available():
                    continue
            elif backend == dist.Backend.NCCL:
                if not dist.is_nccl_available() or not torch.cuda.is_available():
                    continue
            elif backend == dist.Backend.GLOO:
                if not dist.is_gloo_available():
                    continue
            elif backend == dist.Backend.UCC:
                if not dist.is_ucc_available():
                    continue
            elif backend == dist.Backend.XCCL:
                if not dist.is_xccl_available():
                    continue
            # Multi-threaded PG is defined as a pure python class.
            # Its pg.name() does not going through Pybind, so its backend name
            # is still "threaded" instead of "custom".
            elif backend != "threaded":
                excepted_backend = "custom"

            store = dist.FileStore(self.file_name, self.world_size)
            dist.init_process_group(
                backend=backend,
                rank=self.rank,
                world_size=self.world_size,
                store=store,
            )
            pg = c10d._get_default_group()
            self.assertEqual(pg.rank(), self.rank)
            self.assertEqual(pg.size(), self.world_size)
            self.assertEqual(pg.name(), str(excepted_backend))

            dist.destroy_process_group()

    @unittest.skipIf(IS_FBCODE or IS_SANDCASTLE, "subprocess test fails in fbcode")
    def test_default_process_group(self):
        script = """
# Hide all GPUs
import os
os.environ["CUDA_VISIBLE_DEVICES"] = ""

import torch
from torch import distributed as dist

# This should initialize on CPU even though this is a CUDA-enabled build
dist.init_process_group(rank=0, world_size=1, store=dist.HashStore())
"""
        try:
            subprocess.check_output(
                [sys.executable, "-c", script],
                stderr=subprocess.STDOUT,
                # On Windows, opening the subprocess with the default CWD makes `import torch`
                # fail, so just set CWD to this script's directory
                cwd=os.path.dirname(os.path.realpath(__file__)),
                # It is ok to have an extra long timeout here as a timeout means the test failed
                timeout=20,
            )
        except subprocess.TimeoutExpired:
            self.fail(
                msg="Example code timed out! See the code sample in the test for details."
            )
        except subprocess.CalledProcessError as e:
            self.fail(f"""Subprocess failed with {e.output.decode("utf-8")}""")

    def _call_collective_with_varying_tensors(self, backend, collective, *args):
        # call collective with varying tensors to ensure that the tensors are
        # correctly dispatched

        # TODO: this will be updated in the future to not be backend specific
        device = "cuda" if backend == "nccl" else "cpu"
        # ensure supported devices (cpu, cuda) succeeds during dispatch call
        tensor = torch.zeros(2, 2, device=torch.device(device))
        # multi tensor collectives
        if collective == dist.barrier:
            collective()
        elif collective in (dist.all_gather, dist.gather):
            collective([tensor], tensor, *args)
        elif collective == dist.scatter:
            collective(tensor, [tensor], *args)
        elif collective in (dist.reduce_scatter, dist.all_to_all):
            # gloo does not support reduce_scatter or all_to_all
            if backend != "gloo":
                if collective == dist.reduce_scatter:
                    collective(tensor, [tensor], *args)
                else:
                    collective([tensor], [tensor], *args)
        else:
            collective(tensor, *args)

    # TODO: backend will be replaced with a non specified backend
    def _test_collectives(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        collectives_and_args = [
            (dist.reduce, self.rank),
            (dist.broadcast, self.rank),
            (dist.all_reduce,),
            (dist.all_gather,),
            (dist.reduce_scatter,),
            (dist.barrier,),
            (dist.all_to_all,),
            (dist.scatter,),
        ]
        for collective, *args in collectives_and_args:
            with self.subTest(collective=collective, args=args):
                self._call_collective_with_varying_tensors(backend, collective, *args)

    def _test_allreduce_coalesced(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        # TODO: this will be updated in the future to not be backend specific
        device = "cuda" if backend == "nccl" else "cpu"
        tensors = [torch.ones(10, 10, device=torch.device(device))]
        dist.all_reduce_coalesced(tensors, dist.ReduceOp.SUM)
        for tensor in tensors:
            self.assertEqual(tensor, torch.ones(10, 10) * self.world_size)

    def _test_all_to_all_single(self, backend):
        store = dist.FileStore(self.file_name, self.world_size)
        dist.init_process_group(
            backend,
            world_size=self.world_size,
            rank=self.rank,
            store=store,
        )
        device = "cuda" if backend == "nccl" else "cpu"
        # test alltoall_base
        input_tensor = torch.ones(2, 2, device=torch.device(device))
        output_tensor = torch.zeros(2, 2, device=torch.device(device))
        dist.all_to_all_single(output_tensor, input_tensor)

        input_tensor = input_tensor.t()
        with self.assertRaisesRegex(ValueError, "Tensors must be contiguous"):
            dist.all_to_all_single(output_tensor, input_tensor)


class ReduceOpTest(TestCase):
    # Ref: https://github.com/pytorch/pytorch/issues/87191
    def test_op_isinstance_of_reduceop(self):
        for reduce_op in (
            c10d.ReduceOp.SUM,
            c10d.ReduceOp.AVG,
            c10d.ReduceOp.PRODUCT,
            c10d.ReduceOp.MIN,
            c10d.ReduceOp.MAX,
            c10d.ReduceOp.BAND,
            c10d.ReduceOp.BOR,
            c10d.ReduceOp.BXOR,
        ):
            self.assertTrue(isinstance(reduce_op, c10d.ReduceOp))
        for scale in (torch.tensor(1.0), 2.0):
            self.assertTrue(
                isinstance(dist._make_nccl_premul_sum(scale), c10d.ReduceOp)
            )

    # Ref: https://github.com/pytorch/pytorch/pull/87303#discussion_r1002879700
    def test_reduceop_copyable(self):
        for reduce_op in (
            c10d.ReduceOp.SUM,
            c10d.ReduceOp.AVG,
            c10d.ReduceOp.PRODUCT,
            c10d.ReduceOp.MIN,
            c10d.ReduceOp.MAX,
            c10d.ReduceOp.BAND,
            c10d.ReduceOp.BOR,
            c10d.ReduceOp.BXOR,
        ):
            self.assertEqual(copy.copy(reduce_op), reduce_op)
            self.assertEqual(copy.deepcopy(reduce_op), reduce_op)
            self.assertEqual(copy.copy(c10d.ReduceOp(reduce_op)), reduce_op)
            self.assertEqual(copy.deepcopy(c10d.ReduceOp(reduce_op)), reduce_op)

        for scale in (torch.tensor(1.0), 2.0):
            reduce_op = dist._make_nccl_premul_sum(scale)
            self.assertEqual(copy.copy(reduce_op), reduce_op)
            self.assertEqual(copy.deepcopy(reduce_op), reduce_op)

    def test_reduceop_pickle(self):
        for reduce_op in (
            c10d.ReduceOp.SUM,
            c10d.ReduceOp.AVG,
            c10d.ReduceOp.PRODUCT,
            c10d.ReduceOp.MIN,
            c10d.ReduceOp.MAX,
            c10d.ReduceOp.BAND,
            c10d.ReduceOp.BOR,
            c10d.ReduceOp.BXOR,
        ):
            pickle.loads(pickle.dumps(reduce_op))
            orig = c10d.ReduceOp(reduce_op)
            self.assertEqual(pickle.loads(pickle.dumps(orig)), orig)
        for scale in (torch.tensor(1.0), 2.0):
            reduce_op = dist._make_nccl_premul_sum(scale)
            self.assertEqual(pickle.loads(pickle.dumps(reduce_op)), reduce_op)

    # Ref: https://github.com/pytorch/pytorch/issues/90072
    def test_reduceop_equal(self):
        not_reduceop = "abc"
        for reduce_op in (
            c10d.ReduceOp.SUM,
            c10d.ReduceOp.AVG,
            c10d.ReduceOp.PRODUCT,
            c10d.ReduceOp.MIN,
            c10d.ReduceOp.MAX,
            c10d.ReduceOp.BAND,
            c10d.ReduceOp.BOR,
            c10d.ReduceOp.BXOR,
        ):
            reduce_op_obj = c10d.ReduceOp(reduce_op)
            # this calls `ReduceOp.__eq__(self, other)`
            self.assertEqual(reduce_op_obj, reduce_op_obj)
            self.assertEqual(reduce_op_obj, reduce_op)
            self.assertNotEqual(reduce_op_obj, not_reduceop)
            self.assertNotEqual(reduce_op, not_reduceop)
            # TODO(crcrpar): This needs to be `assertEqual` for the associativity even though
            # the comparison of `RedOpType` and `ReduceOp` sounds less likely to happen compared
            # to that of `ReduceOp` and `RedOptype`.
            # this calls `RedOpType.__eq__(self, other)`
            self.assertNotEqual(reduce_op, reduce_op_obj)

            self.assertFalse(None in (reduce_op, reduce_op_obj))
            self.assertFalse(not_reduceop in (reduce_op, reduce_op_obj))


class LocalRankTest(MultiProcessTestCase):
    @property
    def world_size(self):
        return 4

    def setUp(self):
        super().setUp()
        self._spawn_processes()

    def tearDown(self):
        super().tearDown()
        try:
            os.remove(self.file_name)
        except OSError:
            pass

    def testWithoutEnv(self):
        with self.assertRaisesRegex(RuntimeError, "LOCAL_RANK"):
            dist.get_node_local_rank()

    def testWithoutEnvWithFallback(self):
        self.assertEqual(dist.get_node_local_rank(fallback_rank=2), 2)

    def testNodeLocalRankOverridesFallback(self):
        os.environ["LOCAL_RANK"] = str(self.rank)
        self.assertEqual(dist.get_node_local_rank(fallback_rank=123), self.rank)

    def testNodeLocalRank(self):
        os.environ["LOCAL_RANK"] = str(self.rank)
        self.assertEqual(dist.get_node_local_rank(), self.rank)


if __name__ == "__main__":
    assert not torch.cuda._initialized, (
        "test_distributed must not have initialized CUDA context on main process"
    )

    run_tests()