Cocoa线程同步时使用[ALAssetsLibrary enumerateGroupsWithTypes：]

问题描述

我最近像几个人一样发现，[ALAssetsLibrary enumerateGroupsWithTypes]喜欢在另一个主题中执行其方块。很遗憾，苹果没有记录： - ）

在我目前的情况下，我需要等待枚举完成，主线程返回任何结果之前。我显然需要某种类型的线程同步。

我读过关于NSLock& NSConditionLock，但没有什么似乎适合信号一个阻塞的线程，这个工作线程已经完成的要求。看起来像一个简单的需求 - 任何人都可以指向正确的方向？

你的线索&

解决方案

答案是使用NSConditionLock类这样...

  typedef枚举{
 completed = 0，
 running = 1 
} threadState; 
 
 ... 
 
 NSConditionLock * lock = [[NSConditionLock alloc] initWithCondition：running]; 
  

然后分离你的线程，或者在我的例子中调用[ALAssetsLibrary enumerateGroupsWithTypes：]。然后用这个...阻止父线程。

  //等待完成工作线程
 [lock lockWhenCondition：完成]; 
 [lock unlockWithCondition：completed]; 
  

在子/工作线程中完成所有工作后， parent with this ...

  //等待线程信号
 [lock lockWhenCondition：running]; 
 [lock unlockWithCondition：completed]; 
  

I have recently, like a few people, discovered that [ALAssetsLibrary enumerateGroupsWithTypes] likes to run its blocks on another thread. What a shame that Apple didn't document that :-)

In my current circumstance I need to wait for the enumeration to complete, before the main thread returns any results. I clearly need some sort of thread synchronisation.

I've read about NSLock & NSConditionLock, but nothing yet seems to fit the requirement of 'signal a blocked thread that this worker thread has completed'. It seems like a simple enough need - can anyone point me in the right direction?

Your clue & boos, are most welcome as always,

M.

解决方案

The answer is to use the NSConditionLock class thusly ...

typedef enum {
    completed = 0,
    running = 1
} threadState;

...

NSConditionLock *lock = [[NSConditionLock alloc] initWithCondition:running];

Then spin off your thread, or in my case a call to [ALAssetsLibrary enumerateGroupsWithTypes:]. Then block the parent thread with this ...

// Await completion of the worker threads
[lock lockWhenCondition:completed];
[lock unlockWithCondition:completed];

When all work is done in the child/worker thread, unblock the parent with this ...

// Signal the waiting thread
[lock lockWhenCondition:running];
[lock unlockWithCondition:completed];

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