filelock: Make waitcounter variant to use (#139816)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/139816
Approved by: https://github.com/ezyang

test/test_utils_filelock.py

@@ -0,0 +1,53 @@
+# Owner(s): ["module: unknown"]
+import concurrent.futures
+import tempfile
+import time
+
+from torch.testing._internal.common_utils import run_tests, skipIfWindows, TestCase
+from torch.utils._filelock import FileLock
+
+
+class TestFileLock(TestCase):
+    def test_no_crash(self):
+        _, p = tempfile.mkstemp()
+        with FileLock(p):
+            pass
+
+    @skipIfWindows(
+        msg="Windows doesn't support multiple files being opened at once easily"
+    )
+    def test_sequencing(self):
+        with tempfile.NamedTemporaryFile() as ofd:
+            p = ofd.name
+
+            def test_thread(i):
+                with FileLock(p + ".lock"):
+                    start = time.time()
+                    with open(p, "a") as fd:
+                        fd.write(str(i))
+                    end = time.time()
+                    return (start, end)
+
+            with concurrent.futures.ThreadPoolExecutor(max_workers=10) as executor:
+                futures = [executor.submit(test_thread, i) for i in range(10)]
+                times = []
+                for f in futures:
+                    times.append(f.result(60))
+
+            with open(p) as fd:
+                self.assertEqual(
+                    set(fd.read()), {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9"}
+                )
+
+            for i, (start, end) in enumerate(times):
+                for j, (newstart, newend) in enumerate(times):
+                    if i == j:
+                        continue
+
+                    # Times should never intersect
+                    self.assertFalse(newstart > start and newstart < end)
+                    self.assertFalse(newend > start and newstart < end)
+
+
+if __name__ == "__main__":
+    run_tests()