多线程-深入理解GCD

冷不防 2022-09-11 08:24 219阅读 0赞

一，Dispath Queue.

dispatch_async(queue, ^{
        //block
    });

用dispatch\_async这样的函数将block追加到Dispatch Queue中。而block内容便是想执行的任务。而Dispatch Queue，指的就是执行处理的等待队列。Dispatch Queue有着先进先出的原则。他会把你先放进去的任务先拿出来执行。Dispatch Queue有两种，分别为Serial Dispatch Queue 和 Concurrent Dispatch Queue。

Serial Dispatch Queue也就是串行队列，他会一个个把任务拿出来执行，并且在拿下一个任务的时候，上一个任务必须已经是执行完毕了。而Concurrent Dispatch Queue也就是并行队列，他会把任务按照顺序快速的拿出来，因为他不需要等待上一个任务的执行完毕。

二，同步&&异步

同步：阻塞当前线程，必须要等待同步线程中的任务执行完，返回以后，才能继续执行下一任务。  
异步：不会阻塞当前线程，会开启新的线程而不需要等待当前线程的任务执行完毕。

三，同异步与不同队列的组合

### 1.串行队列同步执行： ###

### Serial Dispatch Queue把任务一个个拿出来，线程一个个的执行拿出来的任务。 ###

2.并行队列同步执行：

Concurrent Dispatch Queue会快速的把任务都拿出来，但是线程就只有一个，还是只能一个个得执行任务，所以并没有多线程执行。

3.串行队列异步执行：

Serial Dispatch Queue会把任务一个个拿出来，但拿出下一个前提是上一个任务已经被线程执行完毕了。

4.并行队列异步执行：

这里任务快速拿出，线程快速执行，就实现了多线程操作，提高效率。

四。线程死锁

(1).

- (void)viewDidLoad
    {
        [super viewDidLoad];
        
        NSLog(@"----------1");
        dispatch_sync(dispatch_get_main_queue(), ^{
            NSLog(@"----------2");
        });
        NSLog(@"----------3");
    }

(2).

- (void)viewDidLoad
    {
        [super viewDidLoad];
        
        NSLog(@"----------1");
        dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
            NSLog(@"----------2");
        });
        NSLog(@"----------3");
    }

(3).

- (void)viewDidLoad
    {
        [super viewDidLoad];
        
        NSLog(@"----------1");
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            NSLog(@"----------2");
            dispatch_sync(dispatch_get_main_queue(), ^{
                NSLog(@"----------3");
            });
            NSLog(@"----------4");
        });
        NSLog(@"----------5");
    }

(4).

五。线程总结

1.并发队列 + 同步执行

NSLog(@"syncConcurrent---begin");
        
        dispatch_queue_t queue= dispatch_queue_create("test.queue", DISPATCH_QUEUE_CONCURRENT);
        
        dispatch_sync(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"1------%@",[NSThread currentThread]);
            }
        });
        dispatch_sync(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"2------%@",[NSThread currentThread]);
            }
        });
        dispatch_sync(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"3------%@",[NSThread currentThread]);
            }
        });
        
        NSLog(@"syncConcurrent---end");

2.并发队列 + 异步执行

NSLog(@"asyncConcurrent---begin");
        
        dispatch_queue_t queue= dispatch_queue_create("test.asyncqueue", DISPATCH_QUEUE_CONCURRENT);
        
        dispatch_async(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"1------%@",[NSThread currentThread]);
            }
        });
        dispatch_async(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"2------%@",[NSThread currentThread]);
            }
        });
        dispatch_async(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"3------%@",[NSThread currentThread]);
            }
        });
        
        NSLog(@"asyncConcurrent---end");

3.串行队列 + 同步执行

NSLog(@"syncSerial---begin");
        
        dispatch_queue_t queue = dispatch_queue_create("test.syncSerial", DISPATCH_QUEUE_SERIAL);
        
        dispatch_sync(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"1------%@",[NSThread currentThread]);
            }
        });
        dispatch_sync(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"2------%@",[NSThread currentThread]);
            }
        });
        dispatch_sync(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"3------%@",[NSThread currentThread]);
            }
        });
        
        NSLog(@"syncSerial---end");

4.串行队列 + 异步执行

NSLog(@"asyncSerial---begin");
        
        dispatch_queue_t queue = dispatch_queue_create("test.asyncSerial", DISPATCH_QUEUE_SERIAL);
        
        dispatch_async(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"1------%@",[NSThread currentThread]);
            }
        });
        dispatch_async(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"2------%@",[NSThread currentThread]);
            }
        });
        dispatch_async(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"3------%@",[NSThread currentThread]);
            }
        });
        
        NSLog(@"asyncSerial---end");

5.主队列 + 同步执行

NSLog(@"syncMain---begin");
        
        dispatch_queue_t queue = dispatch_get_main_queue();
        
        dispatch_sync(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"1------%@",[NSThread currentThread]);
            }
        });
        dispatch_sync(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"2------%@",[NSThread currentThread]);
            }
        });
        dispatch_sync(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"3------%@",[NSThread currentThread]);
            }
        });
        
        NSLog(@"syncMain---end");

6.主队列 + 异步执行

NSLog(@"asyncMain---begin");
        
        dispatch_queue_t queue = dispatch_get_main_queue();
        
        dispatch_async(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"1------%@",[NSThread currentThread]);
            }
        });
        dispatch_async(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"2------%@",[NSThread currentThread]);
            }
        });
        dispatch_async(queue, ^{
            for (int i = 0; i < 2; ++i) {
                NSLog(@"3------%@",[NSThread currentThread]);
            }
        });
        
        NSLog(@"asyncMain---end");

7.全局队列+ 异步执行

dispatch_queue_t q = dispatch_get_global_queue(0, 0);
        // 2. 异步执行
        for (int i = 0; i < 10; ++i) {
            dispatch_async(q, ^{
                NSLog(@"asyncGloba：%@ %d", [NSThread currentThread], i);
            });
        }
        NSLog(@"come here");