Dispatch 方法簡介

后臺執行

dispatch_async(dispatch_get_global_queue(0, 0), ^{ //后臺程執行 something; 
}); 

主線程執行

dispatch_async(dispatch_get_main_queue(), ^{// 主線程執行something;
});

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一次性執行

static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{ // 主要用于單例
});

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延遲執行

double delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PE R_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){ // code to be executed on the main queue after delay
});

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創建自定義的線程

dispatch_queue_t myQueue = dispatch_queue_create("com.cnblogs.yybz", NULL); dispatch_async(myQueue, ^{// your code
});

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設置自定義線程的優先級

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dispatch_queue_t myQueue = dispatch_queue_create("com.cnblogs.yybz", NULL); 
dispatch_queue_t globalHightQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0); 
dispatch_set_target_queue(myQueue, globalHighQueue);

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組

dispatch_group_async(group, queue, ^{ // code
}); dispatch_group_wait(group, DISPATCH_TIME_FOREVER); //超時參數 
dispatch_group_notify(group, queue, ^{// code
});dispatch_group_enter(group);
dispatch_async(queue, ^{//code
    dispatch_group_leave(group);
});

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并行同步執行

/**
@parameter iterations 迭代器數量
@parameter queue 提交任務的隊列
@parameter (^block)(size_t) 任務Block,size_t 為迭代器下標
**/
dispatch_apply(size_t iterations, dispatch_queue_t queue, void (^block)(size_t));

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隊列掛起與恢復

dispatch_suspend(queue); 
dispatch_resume(myQueue);

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信號量

dispatch_semaphore_create; //創建一個semaphore
dispatch_semaphore_signal; //發送一個信號
dispatch_semaphore_wait; //等待信號 

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