如何在不使用委托/回调的情况下加入Objective C中的线程？

Question

是否有一种干净的方式来加入Objective C中的线程,就像Java中的"Thread.join"一样？我发现方法performSelector:onThread:withObject:waitUntilDone:但是这个限制是我不能在另一行上调用"阻塞",因为我想做这样的事情:

[dispatch Thread A];
[process something on main thread];
[wait for Thread A to finish before proceeding];

先感谢您.

Answer 1

我不知道有任何Cocoa API可以做到这一点,但它不会太难NSThread做到,使用锁很容易,甚至更容易使用Grand Central Dispatch.

NSThread

NSThread * otherThread = [[NSThread alloc] initWithTarget:self selector:@selector(methodToPerformInBackground:) object:aParameter];
[otherThread start];

//do some stuff

while ([otherThread isFinished] == NO) {
  usleep(1000);
}
[otherThread release];

NSLock

NSLock * lock = [[NSLock alloc] init];

//initiate the background task, which should immediately lock the lock and unlock when done

//do some stuff

[lock lock]; //this will pause until the background stuff unlocks
[lock unlock];
[lock release];

Grand Central Dispatch

dispatch_group_t myGroup = dispatch_group_create();
dispatch_group_async(myGroup, dispatch_get_global_queue(), ^{
  //stuff to do in the background
});

//do some stuff

dispatch_group_wait(myGroup, DISPATCH_TIME_FOREVER);
dispatch_release(myGroup);