GCD初級篇(一)

1. 隊列創(chuàng)建

/**
 隊列創(chuàng)建
 dispatch_queue_create()
 第一個參數(shù)表示隊列的唯一標識符，用于 DEBUG，可為空
 第二個參數(shù) DISPATCH_QUEUE_SERIAL表示串行隊列，DISPATCH_QUEUE_CONCURRENT表示并發(fā)隊列。
 */
- (void)createQueue{
     // 串行隊列創(chuàng)建
    dispatch_queue_t serialQueue = dispatch_queue_create("serial.kelly.com", DISPATCH_QUEUE_SERIAL);
    // 并發(fā)隊列創(chuàng)建
    dispatch_queue_t concurrentQueue = dispatch_queue_create("concurrent.kelly.com", DISPATCH_QUEUE_CONCURRENT);
    // 獲取主隊列:所有放在主隊列中的任務，都會放到主線程中執(zhí)行。
    dispatch_queue_t mainQueue = dispatch_get_main_queue();
    // 對于并發(fā)隊列，GCD 默認提供了全局并發(fā)隊列（Global Dispatch Queue）
    // 第一個參數(shù)優(yōu)先級，第二個填0即可
    dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
}

2. 線程組合運用

2.1 同步執(zhí)行 + 并發(fā)隊列
特點：在當前線程中執(zhí)行任務，不會開啟新線程，執(zhí)行完一個任務，再執(zhí)行下一個任務。

- (void)syncAndConcurrent{
    NSLog(@"當前線程= %@",[NSThread currentThread]);
    NSLog(@"syncAndConcurrent begin ---");
    dispatch_queue_t queue = dispatch_queue_create("syncAndConcurrent.kelly.com", DISPATCH_QUEUE_CONCURRENT);
    dispatch_sync(queue, ^{
        // 模擬耗時2s
        [NSThread sleepForTimeInterval:2];
        NSLog(@"syncAndConcurrent --> 1 當前線程=%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        // 模擬耗時2s
        [NSThread sleepForTimeInterval:2];
        NSLog(@"syncAndConcurrent --> 2 當前線程=%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        // 模擬耗時2s
        [NSThread sleepForTimeInterval:2];
        NSLog(@"syncAndConcurrent --> 3 當前線程=%@",[NSThread currentThread]);
    });
    NSLog(@"syncAndConcurrent end ---");
}
1533817936498.jpg

2.2 異步執(zhí)行 + 并發(fā)隊列
特點：可以開啟多個線程，任務交替（同時）執(zhí)行。

- (void)asyncAndConcurrent{
    NSLog(@"當前線程= %@",[NSThread currentThread]);
    NSLog(@"asyncAndConcurrent begin ---");
    dispatch_queue_t queue = dispatch_queue_create("asyncAndConcurrent.kelly.com", DISPATCH_QUEUE_CONCURRENT);
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"asyncAndConcurrent --> 1 當前線程=%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"asyncAndConcurrent --> 2 當前線程=%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"asyncAndConcurrent --> 3 當前線程=%@",[NSThread currentThread]);
    });
    NSLog(@"asyncAndConcurrent end ---");
}
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2.3 同步執(zhí)行 + 串行隊列
特點：不會開啟新線程，在當前線程執(zhí)行任務。任務是串行的，執(zhí)行完一個任務，再執(zhí)行下一個任務。

- (void)syncAndSerial{
    NSLog(@"當前線程= %@",[NSThread currentThread]);
    NSLog(@"syncAndSerial begin ---");
    dispatch_queue_t queue = dispatch_queue_create("syncAndSerial.kelly.com", DISPATCH_QUEUE_SERIAL);
    
    dispatch_sync(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"syncAndSerial --> 1 當前線程=%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"syncAndSerial --> 2 當前線程=%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"syncAndSerial --> 3 當前線程=%@",[NSThread currentThread]);
    });
    NSLog(@"syncAndSerial end ---");
}
1533818397023.jpg

2.4 異步執(zhí)行 + 串行隊列
會開啟新線程，但是因為任務是串行的，執(zhí)行完一個任務，再執(zhí)行下一個任務。

- (void)asyncAndSerial{
    NSLog(@"當前線程= %@",[NSThread currentThread]);
    NSLog(@"asyncAndSerial begin ---");
    dispatch_queue_t queue = dispatch_queue_create("asyncAndSerial.kelly.com", DISPATCH_QUEUE_SERIAL);
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"asyncAndSerial --> 1 當前線程=%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"asyncAndSerial --> 2 當前線程=%@",[NSThread currentThread]);
    });

    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"asyncAndSerial --> 3 當前線程=%@",[NSThread currentThread]);
    });
    NSLog(@"asyncAndSerial end ---");
}
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2.5 異步執(zhí)行 + 主隊列
特點：只在主線程中執(zhí)行任務，執(zhí)行完一個任務，再執(zhí)行下一個任務

- (void)asyncAndMain{
    NSLog(@"當前線程---%@",[NSThread currentThread]);  // 打印當前線程
    NSLog(@"asyncAndMain---begin");
    dispatch_queue_t queue = dispatch_get_main_queue();
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"syncAndMain --> 1 當前線程=%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"syncAndMain --> 2 當前線程=%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"syncAndMain --> 3 當前線程=%@",[NSThread currentThread]);
    });
    
    NSLog(@"asyncAndMain---end");
}
1533818828690.jpg

2.6 線程間通信

- (void)communication{
    // 獲取全局并發(fā)隊列
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    // 獲取主隊列
    dispatch_queue_t mainQueue = dispatch_get_main_queue();
    // 異步追加任務
    dispatch_async(queue, ^{
       
        [NSThread sleepForTimeInterval:2];
        NSLog(@"gcdCommunication --> 1 當前線程=%@",[NSThread currentThread]);
        // 回到主線程
        dispatch_async(mainQueue, ^{
            // 刷新UI等操作
            [NSThread sleepForTimeInterval:2];
            NSLog(@"gcdCommunication --> 2 當前線程=%@",[NSThread currentThread]);
        });
        
    });
}

3. 多線程其他方法

3.1 柵欄方法 dispatch_barrier_async
dispatch_barrier_async函數(shù)會等待前邊追加到并發(fā)隊列中的任務全部執(zhí)行完畢之后，再將指定的任務追加到該異步隊列中。然后在dispatch_barrier_async函數(shù)追加的任務執(zhí)行完畢之后，異步隊列才恢復為一般動作，接著追加任務到該異步隊列并開始執(zhí)行。

- (void)gcdAndBarrier{
    dispatch_queue_t queue = dispatch_queue_create("gcdAndBarrier.kelly.com", DISPATCH_QUEUE_CONCURRENT);
    NSLog(@"gcdAndBarrier start");
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"gcdAndBarrier -- > 1 當前線程%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"gcdAndBarrier -- > 2 當前線程%@",[NSThread currentThread]);
    });
    
    // 追加barrier
    dispatch_barrier_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"gcdAndBarrier -- > 3 當前線程%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"gcdAndBarrier -- > 4 當前線程%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"gcdAndBarrier -- > 5 當前線程%@",[NSThread currentThread]);
    });
    
}
1533819192522.jpg

3.2 GCD 延時

- (void)gcdAndDelay{
    NSLog(@"currentThread---%@",[NSThread currentThread]);
    NSLog(@"gcdAndDelay---begin");
    dispatch_queue_t queue = dispatch_get_main_queue();
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), queue, ^{
        // 2.0秒后異步追加任務代碼到主隊列，并開始執(zhí)行
        NSLog(@"after---%@",[NSThread currentThread]);
    });
    NSLog(@"gcdAndDelay---end");
}

3.3 隊列組 dispatch_group_notify

- (void)groupNotify {
    NSLog(@"currentThread---%@",[NSThread currentThread]);
    NSLog(@"group---begin");
    
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_queue_t mainQueue = dispatch_get_main_queue();
    
    dispatch_group_async(group, queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"groupNotify 1---%@",[NSThread currentThread]);
    });
    
    dispatch_group_async(group, queue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"groupNotify 2---%@",[NSThread currentThread]);
    });
    
    // 等前面的異步任務1、任務2都執(zhí)行完畢后，回到主線程執(zhí)行下邊任務
    dispatch_group_notify(group, mainQueue, ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"groupNotify 3---%@",[NSThread currentThread]);
        NSLog(@"group---end");
    });
}

3.4 dispatch_group_wait
暫停當前線程（阻塞當前線程），等待指定的 group 中的任務執(zhí)行完成后，才會往下繼續(xù)執(zhí)行。

- (void)groupWait {
    NSLog(@"groupWait---%@",[NSThread currentThread]);
    NSLog(@"group---begin");
    
    dispatch_group_t group = dispatch_group_create();
    
    dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"groupWait 1---%@",[NSThread currentThread]);
    });
    
    dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"groupWait 2---%@",[NSThread currentThread]);
    });
    // 等待上面的任務全部完成后，會往下繼續(xù)執(zhí)行（會阻塞當前線程）
    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
    NSLog(@"group---end");
}
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今天暫時寫這么多，有什么不足的地方，希望各位指出來大家一起學習。

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