Summary:
This diff implements a named pipe based watchdog timer (`FileTimerClient` and `FileTimerServer`). This is similar to the existing `LocalTimerClient` and `LocalTimerServer` (https://fburl.com/code/j4b9pyya).
The motivation is from the need of handling various timeout issues. The training process occasionally get stuck. We need a proper watchdog to monitor the liveness of the training processes. This timer allows the TorchElastic agent (as the watchdog) to monitor the progress of the training processes that it spawned. If a timeout occurred, he TorchElastic agent can take some action to kill the stuck process and creating a core dump for it.
`LocalTimerClient` and `LocalTimerServer` require a `multiprocessing.Queue()` to work. So they can only be used between `multiprocessing` parent and child processes.
`FileTimerClient` and `FileTimerServer` does not have such limitation.
Test Plan:
### Unit Test
```
buck test mode/opt caffe2/test/distributed/elastic/timer:file_based_timer_test
```
```
RemoteExecution session id: reSessionID-06d70a77-043c-4d9d-b0f2-94c24460740a-tpx
Started reporting to test run: https://www.internalfb.com/intern/testinfra/testrun/844425186732666
✓ ListingSuccess: caffe2/test/distributed/elastic/timer:file_based_timer_test : 12 tests discovered (2.177)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_happy_path (file_based_local_timer_test.FileTimerTest) (2.463)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_expired_timers (file_based_local_timer_test.FileTimerServerTest) (1.889)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_send_request_release (file_based_local_timer_test.FileTimerServerTest) (1.700)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_valid_timers (file_based_local_timer_test.FileTimerServerTest) (1.873)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_watchdog_call_count (file_based_local_timer_test.FileTimerServerTest) (1.715)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_watchdog_empty_queue (file_based_local_timer_test.FileTimerServerTest) (1.609)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_exception_propagation (file_based_local_timer_test.FileTimerTest) (1.633)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_multiple_clients_interaction (file_based_local_timer_test.FileTimerTest) (2.189)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_get_timer_recursive (file_based_local_timer_test.FileTimerTest) (2.295)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_no_client (file_based_local_timer_test.FileTimerTest) (1.753)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_timer (file_based_local_timer_test.FileTimerTest) (2.151)
✓ Pass: caffe2/test/distributed/elastic/timer:file_based_timer_test - test_client_interaction (file_based_local_timer_test.FileTimerTest) (1.895)
Summary
Pass: 12
ListingSuccess: 1
Finished test run: https://www.internalfb.com/intern/testinfra/testrun/844425186732666
```
Differential Revision: D38604238
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83695
Approved by: https://github.com/d4l3k
Summary:
Pull Request resolved: https://github.com/pytorch/elastic/pull/148
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56811
Moves docs sphinx `*.rst` files from the torchelastic repository to torch. Note: only moves the rst files the next step is to link it to the main pytorch `index.rst` and write new `examples.rst`
Reviewed By: H-Huang
Differential Revision: D27974751
fbshipit-source-id: 8ff9f242aa32e0326c37da3916ea0633aa068fc5
