On Thu, 2019-08-22 at 10:33 +0300, Nadav Har'El wrote:
> You're right, it seems there's should be a "return" in the recursive
> case!
> That being said, I think the spurious wakeup doesn't cause any harm,
> because the wait code rwlock::writer_wait_lockable() loops, and if a
> thread
> is woken while the lock is still taken, it just goes to sleep again.
> It will just lose it's good spot on the queue :-(
I wasn't sure that was the case. I put an assert in
writer_wait_lockable() (see below) and I was able to trigger it by
having 1 thread take the write lock twice, then a second thread attempt
to take the write lock. When the first thread released, the second
thread triggers the assert.
void rwlock::writer_wait_lockable()
{
while (true) {
if (write_lockable()) {
return;
}
_write_waiters.wait(_mtx);
assert((_wowner == sched::thread::current()) ||
(_wowner == nullptr));
}
}
Rick
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