GPUImage GCD

// set queue attribute
dispatch_queue_attr_t GPUImageDefaultQueueAttribute(void)
{
#if TARGET_OS_IPHONE
    if ([[[UIDevice currentDevice] systemVersion] compare:@"9.0" options:NSNumericSearch] != NSOrderedAscending)
    {
        return dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, 0);
    }
#endif
    return nil;
}

// create queu with attribute  serial  queue
_contextQueue = dispatch_queue_create("com.sunsetlakesoftware.GPUImage.openGLESContextQueue", GPUImageDefaultQueueAttribute());

// set specific
dispatch_queue_set_specific(_contextQueue, openGLESContextQueueKey, (__bridge void *)self, NULL);

// camera - global queue
cameraProcessingQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,0);

// audio global queue   
audioProcessingQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW,0);

// semaphore 信号量    
frameRenderingSemaphore = dispatch_semaphore_create(1);
// 每次保证只能有一个资源执行 
if (dispatch_semaphore_wait(frameRenderingSemaphore, DISPATCH_TIME_NOW) != 0) {
  ...
}

// 完成之后,释放资源            
dispatch_semaphore_signal(frameRenderingSemaphore);


// create 0
    imageUpdateSemaphore = dispatch_semaphore_create(0);

//  signal +1
    dispatch_semaphore_signal(imageUpdateSemaphore);
//  -1
dispatch_semaphore_wait(imageUpdateSemaphore, TIME);

总结:主要用信号量进行资源的控制访问,保证,只有一共在访问它.

创建队列的时候,指定其 队列优先级

特定队列访问资源, dispatch_queue_set_specific 来进行获取设定队列