v3.1/server: Fix PMIx_Server_Finalize hang #1250
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The hang was quite rare and appears as the result of the race condition
between PMIx progress thread and main thread calling
PMIx_Server_finalize.
The following sequence is possible:
| main thread | Progress thread |
| | while(ev_active){ |
| ev_active=0 | |
| ev_break_loop | |
| | ev_loop() |
According to libevent manual, in this situation, libevent will
ignore ev_break_loop as it wasn't in the loop at the time
ev_break_loop() was called (see (b) in the libevent excerpt below)
So the progress thread will enter the loop and hang.
To fix this use event_base_loopexit that have desired behavior
(See section (a) of the excerpt below)
**excerpt from the libevent manual**:
```
...
Note also that event_base_loopexit(base,NULL) and event_base_loopbreak(base)
act differently when no event loop is running:
(a) loopexit schedules the next instance of the event loop to stop right
after the next round of callbacks are run (as if it had been invoked with
EVLOOP_ONCE)
(b) whereas loopbreak only stops a currently running loop, and has no
effect if the event loop isn’t running.
...
```
Signed-off-by: Artem Polyakov <artpol84@gmail.com>
(cherry picked from commit f652ae1)
Conflicts:
src/runtime/pmix_progress_threads.c
artpol84
approved these changes
May 14, 2019
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Corresponds to #1246