Merge branch '5.3' into 5.4

* 5.3:
  [Messenger] Supervisor graceful shutdown

Author: javiereguiluz

messenger.rst

@@ -672,6 +672,23 @@ Next, tell Supervisor to read your config and start your workers:
 
 See the `Supervisor docs`_ for more details.
 
+Graceful Shutdown
+~~~~~~~~~~~~~~~~~
+
+If you install the `PCNTL`_ PHP extension in your project, workers will handle
+the ``SIGTERM`` POSIX signal to finish processing their current message before
+exiting.
+
+In some cases the ``SIGTERM`` signal is sent by Supervisor itself (e.g. stopping
+a Docker container having Supervisor as its entrypoint). In these cases you
+need to add a ``stopwaitsecs`` key to the program configuration (with a value
+of the desired grace period in seconds) in order to perform a graceful shutdown:
+
+.. code-block:: ini
+
+    [program:x]
+    stopwaitsecs=20
+
 .. _messenger-retries-failures:
 
 Retries & Failures
@@ -2211,6 +2228,7 @@ Learn more
 .. _`Enqueue's transport`: https://github.com/sroze/messenger-enqueue-transport
 .. _`streams`: https://redis.io/topics/streams-intro
 .. _`Supervisor docs`: http://supervisord.org/
+.. _`PCNTL`: https://www.php.net/manual/book.pcntl.php
 .. _`SymfonyCasts' message serializer tutorial`: https://symfonycasts.com/screencast/messenger/transport-serializer
 .. _`Long polling`: https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-short-and-long-polling.html
 .. _`Visibility Timeout`: https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-visibility-timeout.html