start_watchdog looped on std::this_thread::sleep_for(watchdog_interval_), and
request_stop() cannot wake a sleeping thread. stop_watchdog()'s join therefore
blocked until the current sleep expired: three seconds on every teardown at
the default interval, and unbounded for anyone who set a long one to keep the
periodic report quiet.
Now a condition_variable_any waited on with the stop token, so request_stop()
ends the wait immediately.
Found while writing the next commit's test, which sets a one-hour interval to
silence the report and consequently hung for an hour in stop().
The test needs one non-obvious thing, and says so: a pause between start() and
stop(). Without it the test races the watchdog — stop_watchdog() runs before
the thread has entered its loop, the token is already set when it does, and it
exits without ever waiting. That passes against the bug as well as the fix,
which is exactly what the first version of this test did.
Verified in both directions: without the fix the case is killed at a 25 s
timeout; with it, stop() returns in 0 ms.
dtourolle
7a3e96cc99