[摘要]本文是對iOS 多線程GCD的基本使用的講解，對學習IOS蘋果軟件開發有所幫助,與大家分享。

《iOS多線程簡介》中提到：GCD中有2個核心概念：1、任務（執行什麼操作）2、隊列（用來存放任務）

那麼多線程GCD的基本使用有哪些呢？

可以分以下多種情況：

1、異步函數 + 並發隊列

/**
 * 異步函數 + 並發隊列：可以同時開啟多條線程
 */
- (void)asyncConcurrent
{
    // 1.創建一個並發隊列
    // dispatch_queue_create(const char *label, dispatch_queue_attr_t attr);
    // label : 相當於隊列的名字
    // dispatch_queue_t queue = dispatch_queue_create("com.kyle.queue", DISPATCH_QUEUE_CONCURRENT);
    
    // 1.獲得全局的並發隊列
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    
    // 2.將任務加入隊列
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i<3; i++) {
            NSLog(@"this is first %@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i<3; i++) {
            NSLog(@"this is second %@",[NSThread currentThread]);
        }
    });
    
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i<3; i++) {
            NSLog(@"this is third %@",[NSThread currentThread]);
        }
    });
    
}

2、同步函數 + 並發隊列

/**
 * 同步函數 + 並發隊列：不會開啟新的線程
 */

- (void)syncConcurrent
{
    // 1.獲得全局的並發隊列
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    
    // 2.將任務加入隊列
    dispatch_sync(queue, ^{
        NSLog(@"this is first %@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"this is second %@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"this is third %@",[NSThread currentThread]);
    });
    
}

3、異步函數 + 串行隊列

/**
 * 異步函數 + 串行隊列：會開啟新的線程，但是任務是串行的，執行完一個任務，再執行下一個任務
 */
- (void)asyncSerial
{
    // 1.創建串行隊列
    dispatch_queue_t queue = dispatch_queue_create("com.kyle.queue", DISPATCH_QUEUE_SERIAL);
    //    dispatch_queue_t queue = dispatch_queue_create("com.kyle.queue", NULL);
    
    // 2.將任務加入隊列
    dispatch_async(queue, ^{
        NSLog(@"this is first %@",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"this is second %@",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"this is third %@",[NSThread currentThread]);
    });
}

4、同步函數 + 串行隊列

/**
 * 同步函數 + 串行隊列：不會開啟新的線程，在當前線程執行任務。任務是串行的，執行完一個任務，再執行下一個任務
 */
- (void)syncSerial
{
    // 1.創建串行隊列
    dispatch_queue_t queue = dispatch_queue_create("com.kyle.queue", DISPATCH_QUEUE_SERIAL);
    
    // 2.將任務加入隊列
    dispatch_sync(queue, ^{
        NSLog(@"this is first %@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"this is second %@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"this is third %@",[NSThread currentThread]);
    });
}

5、異步函數 + 主隊列

// * 異步函數 + 主隊列：只在主線程中執行任務

- (void)asyncMain
{
    // 1.獲得主隊列
    dispatch_queue_t  queue =  dispatch_get_main_queue();
    // 2.將任務加入隊列
    dispatch_async(queue, ^{
        NSLog(@"this is first %@",[NSThread currentThread]);
        NSLog(@"this is second %@",[NSThread currentThread]);
        NSLog(@"this is third %@",[NSThread currentThread]);
    });
}

6、同步函數 + 主隊列

// * 同步函數 + 主隊列：
- (void)syncMain
{
    NSLog(@"begin");
    
    // 1.獲得主隊列
    dispatch_queue_t queue =  dispatch_get_main_queue();
    // 2.將任務加入隊列
    dispatch_sync(queue, ^{
        NSLog(@"this is %@",[NSThread currentThread]);
        
    });
    NSLog(@"end");
}

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