The object server runs certain IO-intensive methods outside the main
pthread for performance. If one of those methods tries to log, this can
cause a crash that eventually leads to an object server with hundreds
or thousands of greenthreads, all deadlocked.
The short version of the story is that logging.SysLogHandler has a
mutex which Eventlet monkey-patches. However, the monkey-patched mutex
sometimes breaks if used across different pthreads, and it breaks in
such a way that it is still considered held. After that happens, any
attempt to emit a log message blocks the calling greenthread forever.
The fix is to use a mutex that works across different greenlets and
across different pthreads. This patch introduces such a lock based on
an anonymous pipe.
Change-Id: I57decefaf5bbed57b97a62d0df8518b112917480
Closes-Bug: 1710328
6d160797fc