The gtid_executed table is range compressed by a background thread,
every N transactions, where N is specified by
@@global.executed_gtids_compression_period. The communication between
a committing client thread and the waiting background thread is done
using a global variable, which indicates whether the compression
thread should wake up or not; a mutex and condition variable, which
the the compression hangs on, and a signal, which the committing
thread sends for the condition variable. However, the protocol for
signalling on condition variables is not followed. The committing
thread does not protect the update of the global variable with the
mutex. So when the compression thread wakes up, it is possible that
the global variable has only been changed in a memory cache that is
only visible to the committing thread. Then the compression thread
will read the old value of the global variable, and think that the
signal was only sent spuriously, and go back to sleep.

To fix the potential problem, The committing thread protects the
update of the global variable with a mutex.