Apple

What is the recipe for this seemingly simple task (that IOSyncer handles
very nicely) with IOCommandGate.

Easy recipe:

Sync Call is made

done = false;

Send I/O asynchronously

IOCommandGate::runAction()

while (!done)

IOCommandGate::commandSleep(&done,TH_UNINT);

On workloop completion thread:

done = true;

IOCommandGate::commandWakeup(&done);

This is very similar to other condition variable like constructs. PThreads programmers will be familiar with this (pthread_mutex_lock()/pthread_cond_wait()/pthread_cond_signal()).

NB: The predicate loop of "while (!done)" is extremely important. An "if" check is insufficient.

Note also that this same thing can be done with a mutex lock and using the sleep/wakeup variants of those (i.e. IOLockSleep()/IOLockWakeup()). Using the IOCommandGate construct makes the taking of the lock "free" on the completion side since the completion should be made with the workloop lock held (and the setting of done = true atomic).

HTH,

-- Chris

------------------

6 Infinite Loop

M/S 306-2MS

Cupertino CA 95014

phone: (408) 974-4033

fax: (408) 862-7577

email: email@hidden

References:
	>IOCommandGate vs ISyncer (From: "Duane Murphy" <email@hidden>)