Problem: pthread condvar timeouts are broken

[lunixbochs]

Problem: pthread condvar timeouts are broken

Solution:

• Use pthread_cond_timedwait_relative_np() on macOS
• Use pthread_cond_timedwait_monotonic_np() on old versions of Android
• Use pthread_condattr_setclock(CLOCK_MONOTONIC) on other platforms

Context: zeromq/czmq#1873 (comment)

[sigiesec]

This is still failing the android build job. Maybe the condition is missing some brackets?

[bluca]

A build failure is introduced in the Android build, could you please fix it?

In file included from src/mailbox_safe.hpp:43:0,
                 from src/mailbox_safe.cpp:31:
src/condition_variable.hpp: In constructor 'zmq::condition_variable_t::condition_variable_t()':
src/condition_variable.hpp:189:58: error: 'pthread_condattr_setclock' was not declared in this scope
         pthread_condattr_setclock (&attr, CLOCK_MONOTONIC);

[bluca]

Is this available on all versions of OSX? There have been many issues with OSX and clocks over the years, see:
#2537
#2538
#1351
#1354

[lunixbochs]

I found pthread_cond_timedwait_relative_np recommended at least 6 years ago for macOS.

For Android, looks like that was the wrong check, and I should just be checking for r21 or not:
https://stackoverflow.com/questions/44580542/ndk-builder-r15-finds-neither-have-pthread-cond-timedwait-monotonic-nor-pthread

[lunixbochs]

It's referenced in https://opensource.apple.com/source/Libc/Libc-166/pthreads.subproj/pthread_cond.c, which is literally OS X 10.0. So yeah I'd say it's probably fine.

[bluca]

Great, thanks for checking

[lunixbochs]

Android build fixed. The clang format build is still erroring, but not on my changes.

[bluca]

Great, thanks for your contribution, merged