Added comments

s3torchconnector/src/s3torchconnector/_s3client/_s3client.py

@@ -32,8 +32,10 @@
 def _identity(obj: Any) -> Any:
     return obj
 
+
 _client_lock = threading.Lock()
 
+
 class S3Client:
     def __init__(
         self,
@@ -53,8 +55,10 @@ def __init__(
 
     @property
     def _client(self) -> MountpointS3Client:
+        # This is a fast check to avoid acquiring the lock unnecessarily.
         if self._client_pid is None or self._client_pid != os.getpid():
             with _client_lock:
+                # This double-check ensures that the client is only created once.
                 if self._client_pid is None or self._client_pid != os.getpid():
                     # `MountpointS3Client` does not survive forking, so re-create it if the PID has changed.
                     self._real_client = self._client_builder()

s3torchconnector/tst/e2e/test_mountpoint_client_parallel_access.py

@@ -6,6 +6,7 @@
 from s3torchconnector._s3client import S3Client
 from s3torchconnectorclient._mountpoint_s3_client import MountpointS3Client
 
+
 class S3ClientWithoutLock(S3Client):
     @property
     def _client(self) -> MountpointS3Client:
@@ -20,11 +21,13 @@ def _client_builder(self):
         time.sleep(1)
         return super()._client_builder()
 
+
 class S3ClientWithLock(S3Client):
     def _client_builder(self):
         time.sleep(1)
         return super()._client_builder()
 
+
 def access_client(client, error_event):
     try:
         if not error_event.is_set():
@@ -34,18 +37,23 @@ def access_client(client, error_event):
         print(f"AssertionError in thread {threading.current_thread().name}: {e}")
         error_event.set()
 
+
 def test_multiple_thread_accessing_mountpoint_client_in_parallel_without_lock():
     print("Running test without lock...")
     client = S3ClientWithoutLock("us-west-2")
     if not access_mountpoint_client_in_parallel(client):
-        pytest.fail("Test failed as AssertionError did not happen in one of the threads.")
+        pytest.fail(
+            "Test failed as AssertionError did not happen in one of the threads."
+        )
+
 
 def test_multiple_thread_accessing_mountpoint_client_in_parallel_with_lock():
     print("Running test with lock...")
     client = S3ClientWithLock("us-west-2")
     if access_mountpoint_client_in_parallel(client):
         pytest.fail("Test failed as AssertionError happened in one of the threads.")
 
+
 def access_mountpoint_client_in_parallel(client):
 
     error_event = threading.Event()
@@ -56,7 +64,14 @@ def access_mountpoint_client_in_parallel(client):
     for i in range(num_accessor_threads):
         if error_event.is_set():
             break
-        accessor_thread = threading.Thread(target=access_client, args=(client, error_event,), name=f"Accessor-{i + 1}")
+        accessor_thread = threading.Thread(
+            target=access_client,
+            args=(
+                client,
+                error_event,
+            ),
+            name=f"Accessor-{i + 1}",
+        )
         accessor_threads.append(accessor_thread)
         accessor_thread.start()