块是在新线程还是原始线程上运行？

Question

如果我有下面定义的方法,传递给方法的块("处理程序")是否在由NSOperationQueue？创建的新线程上调用？或者它被传递到它时所处的线程上调用methodWithCompletionHandler:？

-(void)methodWithCompletionHandler:(void (^)(NSString *message))handler
{
   // Note: We are currently on thread #1. Calling handler(@"my message") here
   //       will run on thread #1.

    NSBlockOperation* someOp = [NSBlockOperation blockOperationWithBlock: ^{

   // do some stuff
   }];

   [someOp setCompletionBlock:^{
      // Note: Now someOp is completing, but it's in thread #2. Does calling the handler
      //       as below also run in thread #2 or thread #1?
      handler(@"Some message.");
   }];

   NSOperationQueue *queue = [NSOperationQueue new];
   [queue addOperation:someOp];
}

Answer 1

从文档:

您的完成块的确切执行上下文无法保证,但通常是辅助线程.

http://developer.apple.com/library/ios/documentation/Cocoa/Reference/NSOperation_class/Reference/Reference.html#//apple_ref/doc/uid/TP40004591-RH2-SW36