The Debug Sync facility allows placement of synchronization points
in the code. They can be activated by statements that set the
debug_sync system variable. An active
synchronization point can emit a signal or wait for a signal to be
emitted by another thread. This waiting times out after 300
seconds by default. The
option for mysql-test-run.pl changes that
N seconds. A timeout of zero
disables the facility altogether, so that synchronization points
will not emit or wait for signals, even if activated.
The purpose of the timeout is to avoid a complete lockup in test cases. If for some reason the expected signal is not emitted by any thread, the execution of the affected statement will not block forever. A warning shows up when the timeout happens. That makes a difference in the test result so that it will not go undetected.
For test cases that require the Debug Sync facility, include the following line in the test case file:
For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.