NSBlockOperation

 NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{

        NSLog(@"1--%@",[NSThread currentThread]);

    }];

    NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{

        NSLog(@"2--%@",[NSThread currentThread]);

    }];

    NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{

        NSLog(@"3--%@",[NSThread currentThread]);

    }];

    [op1start];

    [op2start];

    [op3start];

在上述情况中,是不会开启子线程的,看图一打印结果

图一

如果对 op3追加三个任务

  [op3addExecutionBlock:^{

        NSLog(@"4--%@",[NSThread currentThread]);

    }];

    [op3addExecutionBlock:^{

         NSLog(@"5--%@",[NSThread currentThread]);

    }];

    [op3addExecutionBlock:^{

         NSLog(@"6--%@",[NSThread currentThread]);

    }];

此时在看打印结果

图二

可以从图二中看出来,追加了三个任务后,确实开了子线程,但是这个三个子线程不一定就是4,5,6的子线程,需要注意.