Re: dispatch_sync(dispatch_get_main_queue() UI weirdness
Re: dispatch_sync(dispatch_get_main_queue() UI weirdness
- Subject: Re: dispatch_sync(dispatch_get_main_queue() UI weirdness
- From: Quincey Morris <email@hidden>
- Date: Fri, 05 Sep 2014 20:48:52 +0000
On Sep 5, 2014, at 13:31 , Jonathan Guy <email@hidden> wrote:
> The callback is basically structured like this
>
> __block BOOL accept;
>
> if ([NSThread isMainThread]) {
> accept = [[Controller sharedController] shouldIAccept:certInfo];
> }
> else {
> dispatch_sync(dispatch_get_main_queue(), ^{
> accept = [[Controller sharedController] shouldIAccept:certInfo];
> // This is where UI starts playing up when the controller shows the cert
> });
> }
>
> return accept;
>
> So the shouldIAccept method needs to block hence runModal. I also just threw the window up and created my own modal loop but same problem.
It seems to me you’re *still* abusing the main thread. A dispatch_sync blocks the main thread, so it can’t be allowed to do anything that run asynchronously on the main thread (such as displaying a dialog) since that won’t complete.
I suggest you approach this by denying yourself the use of dispatch_sync. I don’t know if Jens will have a better approach, but I’d be inclined to do it with a semaphore (dispatch_semaphore_t) protecting the ‘accept’ variable, and a dispatch_async to the main queue to ask the user what to do. GCD semaphores are incredibly easy to use.
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