[Lazarus] Application.QueueAsyncCall()

cobines cobines at gmail.com
Thu Jan 21 03:01:39 CET 2010

2010/1/21 Brad Campbell <brad at wasp.net.au>:
> Yeah, but what I'm trying to do is have the main gui thread sit on its hands
> until it has a message waiting for it. Then I'd like to have it wakeup on an
> event rather than spinning or polling, while still remaining responsive to
> user input.

Polling is the only way to check for messages. If you block the main
thread waiting for an event your application will be unresponsive; it
needs to be in a constant loop. The async queue is checked every
iteration so eventually your callback will be called.

> Unless I'm mistaken (and I'm pretty green at thread stuff still) it looks
> like you are running a separate thread that checks a message queue and runs
> the callbacks from there, so you are possibly updating gui components from a
> thread other than the main thread. Is that kosher?

No, the callbacks are run from CallMethods() which is called via
Synchronize(), so they are run from the main thread. But instead of
the thread that queued the callback being blocked it is the thread
from GuiMessageQueue that is blocked. That way a worker thread can run

If you're not worried about your worker thread pausing from time to
time to update the GUI, then using Synchronize is prefferable.


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