1. dispatch_barrier_async
例子1.1：
- (void)testGCD_Barrier {
dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
[NSThread sleepForTimeInterval:1.0];
NSLog(@"Task 1,%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"Task 2,%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"Task 3,%@",[NSThread currentThread]);
});
dispatch_barrier_async(queue, ^{
[NSThread sleepForTimeInterval:1.0];
NSLog(@"barrier");
});
NSLog(@"running1, %@", [NSThread currentThread]);
dispatch_async(queue, ^{
NSLog(@"Task 4,%@",[NSThread currentThread]);
});
NSLog(@"running2, %@", [NSThread currentThread]);
dispatch_async(queue, ^{
NSLog(@"Task 5,%@",[NSThread currentThread]);
});
}
结果1.1：
2020-04-16 12:42:22.483987+0800 Task 3,<NSThread: 0x600003cdeac0>{number = 4, name = (null)}
2020-04-16 12:42:22.483983+0800 running1, <NSThread: 0x600003cc60c0>{number = 1, name = main}
2020-04-16 12:42:22.483986+0800 Task 2,<NSThread: 0x600003c99e00>{number = 6, name = (null)}
2020-04-16 12:42:22.484120+0800 running2, <NSThread: 0x600003cc60c0>{number = 1, name = main}
2020-04-16 12:42:23.484001+0800 Task 1,<NSThread: 0x600003ca9e40>{number = 7, name = (null)}
2020-04-16 12:42:24.487740+0800 barrier
2020-04-16 12:42:24.488144+0800 Task 4,<NSThread: 0x600003ca9e40>{number = 7, name = (null)}
2020-04-16 12:42:24.488144+0800 Task 5,<NSThread: 0x600003c6bb40>{number = 8, name = (null)}
结论1.1：
使用
dispatch_queue_create的话
- Task1、2、3在子线程异步执行，都在barrier的前面，Task4、5在barrier的后面异步执行。
- barrier会等待Task1、2、3都执行完毕才会执行。
- running1和running2不必等待barrier执行完就在当前线程（主线程）执行了。
例子1.2：
- (void)testGCD_Barrier {
dispatch_queue_t queue = dispatch_get_main_queue();
dispatch_async(queue, ^{
[NSThread sleepForTimeInterval:1.0];
NSLog(@"Task 1,%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"Task 2,%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"Task 3,%@",[NSThread currentThread]);
});
dispatch_barrier_async(queue, ^{
[NSThread sleepForTimeInterval:1.0];
NSLog(@"barrier");
});
NSLog(@"running1, %@", [NSThread currentThread]);
dispatch_async(queue, ^{
NSLog(@"Task 4,%@",[NSThread currentThread]);
});
NSLog(@"running2, %@", [NSThread currentThread]);
dispatch_async(queue, ^{
NSLog(@"Task 5,%@",[NSThread currentThread]);
});
}
结果1.2：
2020-04-16 12:33:17.270059+0800 running1, <NSThread: 0x600002f40540>{number = 1, name = main}
2020-04-16 12:33:17.270197+0800 running2, <NSThread: 0x600002f40540>{number = 1, name = main}
2020-04-16 12:33:18.287278+0800 Task 1,<NSThread: 0x600002f40540>{number = 1, name = main}
2020-04-16 12:33:18.287470+0800 Task 2,<NSThread: 0x600002f40540>{number = 1, name = main}
2020-04-16 12:33:18.287596+0800 Task 3,<NSThread: 0x600002f40540>{number = 1, name = main}
2020-04-16 12:33:19.288755+0800 barrier
2020-04-16 12:33:19.289002+0800 Task 4,<NSThread: 0x600002f40540>{number = 1, name = main}
2020-04-16 12:33:19.289125+0800 Task 5,<NSThread: 0x600002f40540>{number = 1, name = main}
结论1.2：
使用
dispatch_get_main_queue的话
- Task1、2、3、barrier、4、5就直接在主线程顺序执行了。
- 因为Task1让线程（此时就是主线程）休眠了1秒，所以Task2、3也就在Task1后执行。
- 一般也不会搭配
dispatch_get_main_queue使用，没啥实际意义。
2. dispatch_barrier_sync
例子2.1：
- (void)testGCD_Barrier {
dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
[NSThread sleepForTimeInterval:1.0];
NSLog(@"Task 1,%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"Task 2,%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"Task 3,%@",[NSThread currentThread]);
});
dispatch_barrier_sync(queue, ^{
[NSThread sleepForTimeInterval:1.0];
NSLog(@"barrier");
});
NSLog(@"running1, %@", [NSThread currentThread]);
dispatch_async(queue, ^{
NSLog(@"Task 4,%@",[NSThread currentThread]);
});
NSLog(@"running2, %@", [NSThread currentThread]);
dispatch_async(queue, ^{
NSLog(@"Task 5,%@",[NSThread currentThread]);
});
}
结果2.1：
2020-04-16 12:45:04.678625+0800 Task 2,<NSThread: 0x6000009bbac0>{number = 4, name = (null)}
2020-04-16 12:45:04.678638+0800 Task 3,<NSThread: 0x600000997900>{number = 6, name = (null)}
2020-04-16 12:45:05.678649+0800 Task 1,<NSThread: 0x6000009a17c0>{number = 3, name = (null)}
2020-04-16 12:45:06.679074+0800 barrier
2020-04-16 12:45:06.679572+0800 running1, <NSThread: 0x6000009e2680>{number = 1, name = main}
2020-04-16 12:45:06.679873+0800 running2, <NSThread: 0x6000009e2680>{number = 1, name = main}
2020-04-16 12:45:06.679975+0800 Task 4,<NSThread: 0x6000009a2680>{number = 5, name = (null)}
2020-04-16 12:45:06.681213+0800 Task 5,<NSThread: 0x6000009a17c0>{number = 3, name = (null)}
结论2.1：
使用
dispatch_queue_create的话
- Task1、2、3在子线程异步执行，都在barrier的前面，Task4、5在barrier的后面异步执行。
- running1和running2必须等待barrier执行完才会在当前线程（主线程）执行，也就是
dispatch_barrier_sync会阻塞当前线程，因此dispatch_barrier_sync也就可能造成线程锁死。
例子2.2：
- (void)testGCD_Barrier {
dispatch_queue_t queue = dispatch_get_main_queue();
dispatch_async(queue, ^{
[NSThread sleepForTimeInterval:1.0];
NSLog(@"Task 1,%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"Task 2,%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"Task 3,%@",[NSThread currentThread]);
});
dispatch_barrier_sync(queue, ^{
[NSThread sleepForTimeInterval:1.0];
NSLog(@"barrier");
});
NSLog(@"running1, %@", [NSThread currentThread]);
dispatch_async(queue, ^{
NSLog(@"Task 4,%@",[NSThread currentThread]);
});
NSLog(@"running2, %@", [NSThread currentThread]);
dispatch_async(queue, ^{
NSLog(@"Task 5,%@",[NSThread currentThread]);
});
}
结果2.2:
直接就崩了
image.png
结论2.2：
dispatch_barrier_sync不能与dispatch_get_main_queue结合使用。
注意事项：
-
dispatch_barrier_(a)sync一般搭配自定义并行队列dispatch_queue_t使用。 - 如果搭配
dispatch_get_global_queue，其作用和dispatch_(a)sync一样了没有实际使用意义。 - 一般也搭配
dispatch_get_main_queue使用，dispatch_barrier_sync还会导致crash。
网友评论