Poco::Condition

[micheleselea]

Hi @obiltschnig @aleks-f I have a question about Condition class.
Why we need an external mutex, and why is used in tryWait like that?

{
		ScopedUnlock<Mtx> unlock(mutex, false);
		Event event;
		{
			FastMutex::ScopedLock lock(_mutex);
			mutex.unlock();
			enqueue(event);
		}
		if (!event.tryWait(milliseconds))
		{
			FastMutex::ScopedLock lock(_mutex);
			dequeue(event);
			return false;
		}
		return true;
	}

I can't undertand the reason

[bas524]

You can see, that standard lib does the same, for example Microsoft STL
https://github.com/microsoft/STL/blob/main/stl/inc/condition_variable#L234

[aleks-f]

To be locked until condition is satisfied, that's how condition works:

Atomically unlocks lock, blocks the current executing thread, and adds it to the list of threads waiting on *this. The thread will be
unblocked when notify_all() or notify_one()
is executed. It may also be unblocked spuriously. When
unblocked, regardless of the reason, lock is reacquired and wait exits.

[micheleselea]

ok understood