asyncAndWait(execute:)
Submits a work item for execution and returns only after it finishes executing.
Declaration
func asyncAndWait(execute block: () -> Void)Parameters
- block:
The block that contains the work to perform. This block has no return value and no parameters. This parameter cannot be
NULL.
Discussion
This function submits work to the specified queue for execution. Unlike dispatch_async, this function does not return until after the block finishes. Calling this function and targeting the current queue results in deadlock.
Unlike sync(execute:), this function respects all attributes of the queue when it executes the block. For example, it respects the quality-of-service level and autorelease frequency of the target queue.
If the runtime has already brought up a thread to service asynchronous work items, the system uses that same thread to execute any synchronous blocks you submitted using this function. If the runtime hasn’t brought up a thread to service asynchronous work items, the sytem executes these synchronous blocks on the current thread as an optimization. However, these optimizations apply only when queue targets a global concurrent queue. If it targets any other queue, the system executes the work on that queue’s thread. For example, if queue targets the main queue, the block always runs on the main thread.
Unlike with dispatch_async, no retain is performed on the target queue. Because calls to this function are synchronous, it “borrows” the reference of the caller. Moreover, no Block_copy is performed on the block.