AEAudioControllerSendAsynchronousMessageToMainThread

Brendt

Hi,

I'm trying to send a message via AEAudioControllerSendAsynchronousMessageToMainThread using the code below and pass through my PlaybackManager class so that I can send it a message on the main thread.

I'm getting a crash on the first line of the pageTurnHandler and need some help to figure out why as I'm not that experienced working with C.

Below is my code.

Thanks
Brendt

#pragma mark - Audio Timing Callback
-(AEAudioControllerTimingCallback)timingReceiverCallback
{
    return playbackTimingReceiver;
}

static void playbackTimingReceiver(PlaybackManager* receiver,
                                   AEAudioController *audioController,
                                   const AudioTimeStamp *time,
                                   UInt32 const frames,
                                   AEAudioTimingContext context)
{
    receiver->_hostTime = getUptimeInMilliseconds(time->mHostTime);
    AEAudioControllerSendAsynchronousMessageToMainThread(audioController,
                                                         pageTurnHandler,
                                                         &receiver,
                                                         sizeof(id));
    
}

static void pageTurnHandler(AEAudioController *audioController, void *userInfo, int userInfoLength)
{
    PlaybackManager* receiver = (__bridge PlaybackManager*)userInfo;
    NSLog(@Receiver:%@", receiver);
}

Michael

Your crash is happening because you need to dereference userInfo once more.

AEAudioControllerSendAsynchronousMessageToMainThread will copy the value of the third argument (of length given by the fourth argument) - you've got that call correct, as you're passing the pointer to the id. But then in pageTurnHandler, you're treating userInfo as a PlaybackManager*, which it isn't: userInfo is a pointer to a memory area containing a PlaybackManager*. That is, it's a PlaybackManager**.

So, you need at extra dereference:

PlaybackManager* receiver = *((__bridge PlaybackManager**)userInfo);

Um.. at least I think that's how you'd do it in an ARC-friendly way. Not sure if the compiler would complain about __bridge being used with something that isn't a pointer to an object. You might need to use (__bridge PlaybackManager*)*((PlaybackManager**)userInfo) if that doesn't work. Let me know either way, cos I'm interested

Brendt

Thanks for your quick response Michael much appreciated.

I tried:

PlaybackManager* receiver = *((__bridge PlaybackManager**)userInfo);

compiler complains with:
Pointer to non-const type 'PlaybackManager *' with no explicit ownership
Incompatible types casting 'void *' to 'PlaybackManager *__strong' with a __bridge cast

and for

PlaybackManager* receiver = (__bridge PlaybackManager*)*((PlaybackManager**)userInfo);

compiler complains with:
Pointer to non-const type 'PlaybackManager *' with no explicit ownership
Incompatible type casting 'PlaybackManager *' to 'PlaybackManager *' with a __bridge case

Michael

Haha. Ahh. Um... I'm afraid your guess is as good as mine regarding that syntax, then. I'm personally not using ARC in my audio code as the last time I attempted a migration a couple years back it added more complexity than it removed due to all the C structures/etc I was using.

So... You're on your own there

Brendt

Hmm, what is the syntax without ARC? As maybe it is worth me switching it off for this class to make things easier...

I've been researching and playing around and just can't get the complier quite.

Michael

 PlaybackManager* receiver = *((PlaybackManager**)userInfo);

seabass223

I spent a good amount of time on this today. Just to keep the conversation going, Brendt had his answer resolved here-> http://stackoverflow.com/questions/17735638/dereference-pointer-with-arc-in-c-function-in-ios

ata_nm

This post is really old and TAAE went through a second version and is now completely deprecated! (VERY SAD )
However, if anyone comes across this ARC issue, here is my fix:

PlaybackManager *audioBufferPlayer = *(__weak PlaybackManager **)userInfo;

Just be sure to check for nil when accessing