dispatch打印结果

代码面试题

以下代码打印结果分别是什么？

NSLog(@"%@, 1", [NSThread currentThread]);
dispatch_queue_t queue = dispatch_queue_create("com.test.queue", NULL);
dispatch_sync(queue, ^{
    NSLog(@"%@, 2", [NSThread currentThread]);
});
NSLog(@"3");
NSLog(@"------分割线------");
NSLog(@"%@, 1", [NSThread currentThread]);
dispatch_queue_t queue1 = dispatch_queue_create("com.test.queue", NULL);
dispatch_async(queue1, ^{
    NSLog(@"%@, 2", [NSThread currentThread]);
});
NSLog(@"3");
NSLog(@"------分割线------");
NSLog(@"%@, 1", [NSThread currentThread]);
dispatch_queue_t queue2 = dispatch_queue_create("com.test.queue", DISPATCH_QUEUE_CONCURRENT);
dispatch_sync(queue2, ^{
    NSLog(@"%@, 2", [NSThread currentThread]);
});
NSLog(@"3");
NSLog(@"------分割线------");
NSLog(@"%@, 1", [NSThread currentThread]);
dispatch_queue_t queue3 = dispatch_queue_create("com.test.queue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue3, ^{
    for (int i = 0; i < 2; i++) {
        NSLog(@"block1 %@", [NSThread currentThread]);
    }
});
dispatch_async(queue3, ^{
    for (int i = 0; i < 2; i++) {
        NSLog(@"block2 %@", [NSThread currentThread]);
    }
});
NSLog(@"3");
NSLog(@"------分割线------");
NSLog(@"%@, 1", [NSThread currentThread]);
dispatch_queue_t queue4 = dispatch_get_main_queue();
dispatch_sync(queue4, ^{
    NSLog(@"%@, 2", [NSThread currentThread]);
});
NSLog(@"3");
NSLog(@"------分割线------");
NSLog(@"%@, 1", [NSThread currentThread]);
dispatch_queue_t queue5 = dispatch_get_main_queue();
dispatch_async(queue5, ^{
    for (int i = 0; i < 2; i++) {
        NSLog(@"block1 %@", [NSThread currentThread]);
    }
});
dispatch_async(queue5, ^{
    for (int i = 0; i < 2; i++) {
        NSLog(@"block2 %@", [NSThread currentThread]);
    }
});
NSLog(@"3");