Description of problem:

With the current implementation of timers in gluster, there are some situations that cannot be handled in a safe way. This could lead to race conditions, causing crashes or other unexpected side effects.

Version-Release number of selected component (if applicable): master

Additional info:

A clear example is the release of resources after cancelling a timer (the timer could have not been really cancelled and the callback will run anyway but the caller of gf_timer_call_cancel() has no way to know it).

Additionally, it's not possible to determine if a timer callback has been executed or not, or synchronize with it and know if it has been executed successfully.