GCD常用方法

//同步: 不會開啟新線程(特點:阻塞當前線程)
//異步: 具備開辟新線程的能力,但是并不一定開辟新線程(特點:不會阻塞當前線程)

//串行: 先進先出,必須完成上一個任務,才能執行下一個任務
//并發:

//同步和異步: 針對的是線程
//串行和并發: 針對的是隊列

//多線程,會消耗CPU的資源: 一條子線程占512kb的內存,主線程占1M內存
//多線程原理: CPU在不同線程之間快速切換

//任務: block代碼塊
//死鎖: 2個任務相互等待.你等我執行完,我等你執行完

//同步并發
- (void)syncConcurrent {
    NSLog(@"begin");
    dispatch_queue_t queue = dispatch_queue_create("com.gcd", DISPATCH_QUEUE_CONCURRENT);
    dispatch_sync(queue, ^{
        NSLog(@"任務1, %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"任務2, %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"任務3, %@", [NSThread currentThread]);
    });
    NSLog(@"end");
}

//異步并發
- (void)asyncConcurrent {
    NSLog(@"begin");
    dispatch_queue_t queue = dispatch_queue_create("com.gcd", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        NSLog(@"任務1, %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"任務2, %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"任務3, %@", [NSThread currentThread]);
    });
    NSLog(@"end");
}

//異步串行
- (void)asyncSerial {
    NSLog(@"begin");
    dispatch_queue_t queue = dispatch_queue_create("com.gcd", DISPATCH_QUEUE_SERIAL);
    dispatch_async(queue, ^{
        NSLog(@"任務1, %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"任務2, %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"任務3, %@", [NSThread currentThread]);
    });
    NSLog(@"end");
}

//同步串行
- (void)syncSerial {
    NSLog(@"begin");
    dispatch_queue_t queue = dispatch_queue_create("com.gcd", DISPATCH_QUEUE_SERIAL);
    dispatch_sync(queue, ^{
        NSLog(@"任務1, %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"任務2, %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"任務3, %@", [NSThread currentThread]);
    });
    NSLog(@"end");
}

//同步并發嵌套(同步)
- (void)syncConcurrent_sync {
    NSLog(@"begin");
    dispatch_queue_t queue = dispatch_queue_create("com.gcd", DISPATCH_QUEUE_CONCURRENT);
    dispatch_sync(queue, ^{
        NSLog(@"任務1, %@", [NSThread currentThread]);
        dispatch_async(queue, ^{
            NSLog(@"任務2, %@", [NSThread currentThread]);
        });
        NSLog(@"任務3, %@", [NSThread currentThread]);
    });
    NSLog(@"end");
}

//同步并發嵌套(異步)
- (void)syncConcurrent_async {
    NSLog(@"begin");
    dispatch_queue_t queue = dispatch_queue_create("com.gcd", DISPATCH_QUEUE_CONCURRENT);
    dispatch_sync(queue, ^{
        NSLog(@"任務1, %@", [NSThread currentThread]);
        dispatch_async(queue, ^{
            NSLog(@"任務2, %@", [NSThread currentThread]);
        });
        NSLog(@"任務3, %@", [NSThread currentThread]);
    });
    NSLog(@"end");
}

//同步串行嵌套(異步)
- (void)syncSerial_async {
    NSLog(@"begin");
    dispatch_queue_t queue = dispatch_queue_create("com.gcd", DISPATCH_QUEUE_SERIAL);
    dispatch_sync(queue, ^{
        NSLog(@"任務1, %@", [NSThread currentThread]);
        dispatch_async(queue, ^{
            NSLog(@"任務2, %@", [NSThread currentThread]);
        });
        NSLog(@"任務3, %@", [NSThread currentThread]);
    });
    NSLog(@"end");
}

//異步串行嵌套(異步)
- (void)asyncSerial_async {
    NSLog(@"begin");
    dispatch_queue_t queue = dispatch_queue_create("com.gcd", DISPATCH_QUEUE_SERIAL);
    dispatch_async(queue, ^{
        NSLog(@"任務1, %@", [NSThread currentThread]);
        dispatch_async(queue, ^{
            NSLog(@"任務2, %@", [NSThread currentThread]);
        });
        NSLog(@"任務3, %@", [NSThread currentThread]);
    });
    NSLog(@"end");
}

//異步串行嵌套(同步)--->死鎖
- (void)asyncSerial_sync {
    NSLog(@"begin");
    dispatch_queue_t queue = dispatch_queue_create("com.gcd", DISPATCH_QUEUE_SERIAL);
    dispatch_async(queue, ^{//block1
        NSLog(@"任務1, %@", [NSThread currentThread]);
        dispatch_sync(queue, ^{//block2
            NSLog(@"任務2, %@", [NSThread currentThread]);
        });
        NSLog(@"任務3, %@", [NSThread currentThread]);
    });
    NSLog(@"end");
    //block1和block2兩個任務死鎖
}


//1、創建主線程（串行）
dispatch_async(dispatch_get_main_queue(), ^{
    //刷新界面代碼
});

    //2、創建異步線程（并行）
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        //比較耗時的代碼放這里
    });

    //3、gcd延遲
    double delayInSeconds = 1.0;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        //延遲代碼
    });

    //4、gcd只執行一次
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        //只執行一次代碼
    });

    //5、有三個任務，需要異步并發執行前兩個任務，前兩個任務執行完成后再執行第三個任務。
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        
        //創建組
        dispatch_group_t group=dispatch_group_create();
        
        // 關聯一個任務到group
        dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            //任務一
            NSLog(@"******執行任務一******");
        });
        
        // 關聯一個任務到group
        dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            //任務二
            NSLog(@"******執行任務二******");
        });
        
        // 等待組中的任務執行完畢,回到主線程執行block回調
        dispatch_group_notify(group, dispatch_get_main_queue(), ^{
            //任務三
            NSLog(@"******等待組中的任務執行完畢,回到主線程執行block回調,執行任務三******");
        });
        
    });

 //6、dispatch_barrier_async的使用，dispatch_barrier_async是在前面的任務執行結束后它才執行，而且它后面的任務等它執行完成之后才會執行
    dispatch_queue_t queue = dispatch_queue_create("create_asy_queue", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        NSLog(@"dispatch_async1");
    });
    dispatch_async(queue, ^{
        NSLog(@"dispatch_async2");
    });
    dispatch_barrier_async(queue, ^{
        NSLog(@"dispatch_barrier_async");
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"刷新界面");
        });
        
    });
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"dispatch_async3");
    });

    /*7、GCD的另一個用處是可以讓程序在后臺較長久的運行。
    在沒有使用GCD時，當app被按home鍵退出后，app僅有最多5秒鐘的時候做一些保存或清理資源的工作。但是在使用GCD后，app最多有10分鐘的時間在后臺長久運行。這個時間可以用來做清理本地緩存，發送統計數據等工作。
    讓程序在后臺長久運行的示例代碼如下：
    */
    // AppDelegate.h文件
    @property (assign, nonatomic) UIBackgroundTaskIdentifier backgroundUpdateTask;
    
    // AppDelegate.m文件
    - (void)applicationDidEnterBackground:(UIApplication *)application
    {
        [self beingBackgroundUpdateTask];
        // 在這里加上你需要長久運行的代碼
        [self endBackgroundUpdateTask];
    }
    
    - (void)beingBackgroundUpdateTask
    {
        self.backgroundUpdateTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
            [self endBackgroundUpdateTask];
        }];
    }
    
    - (void)endBackgroundUpdateTask
    {
        [[UIApplication sharedApplication] endBackgroundTask: self.backgroundUpdateTask];
        self.backgroundUpdateTask = UIBackgroundTaskInvalid;
    }
最后編輯于 ：
?著作權歸作者所有,轉載或內容合作請聯系作者
平臺聲明：文章內容（如有圖片或視頻亦包括在內）由作者上傳并發布，文章內容僅代表作者本人觀點，簡書系信息發布平臺，僅提供信息存儲服務。