使块在串行队列中等待

Question

I am using a serial queue in GCD like

dispatch_queue_t myCustomQueue;
myCustomQueue = dispatch_queue_create("com.example.MyCustomQueue", NULL);

dispatch_async(myCustomQueue, ^{
    ....
/* some asyncronus call*/

});

in the block i want to make a asynchronous call like playing a audio,

My main problem is as soon as i am making a asynchronous call the block is not waiting and it completes the execution of whole block.

Can i make the block wait for some time until some callback from the asynchronous call returns

Answer 1

The block cannot wait, but the thread who is exceuting it can.

Look into NSCondition which enables you to wait and signal threads

Basically you allocate a NSCondition and in the block you'll have [condition wait]; which will cause the thread to wait. then, when the async operation is done, you call [condition signal]; which will signal the waiting thread to continue.