dispatch_queue_t queue &＃61; dispatch_queue_create("Database_Queue", DISPATCH_QUEUE_CONCURRENT);dispatch_async(queue, ^{NSLog(&＃64;"reading data1");});dispatch_async(queue, ^{NSLog(&＃64;"reading data2");});dispatch_barrier_async(queue, ^{NSLog(&＃64;"writing data1");[NSThread sleepForTimeInterval:1];});dispatch_async(queue, ^{[NSThread sleepForTimeInterval:1];NSLog(&＃64;"reading data3");});
执行结果如下&＃xff1a;
GCDTests[13360:584316] reading data2GCDTests[13360:584317] reading data1GCDTests[13360:584317] writing data1GCDTests[13360:584317] reading data3
我们将写数据的操作放在dispatch_barrier_async中&＃xff0c;这样能确保在写数据的时候会等待前面的读操作完成&＃xff0c;而后续的读操作也会等到写操作完成后才能继续执行&＃xff0c;提高文件读写的执行效率。
dispatch_queue_t queue &＃61; dispatch_queue_create("myqueue", DISPATCH_QUEUE_CONCURRENT);//并发的运行一个block任务5次dispatch_apply(5, queue, ^(size_t i) {NSLog(&＃64;"do a job %zu times",i&＃43;1);});NSLog(&＃64;"go on");
输出结果&＃xff1a;
GCDTests[10029:760640] do a job 2 timesGCDTests[10029:760640] do a job 1 timesGCDTests[10029:760640] do a job 3 timesGCDTests[10029:760640] do a job 5 timesGCDTests[10029:760640] do a job 4 timesGCDTests[10029:760640] go on
void dispatch_block_notify(dispatch_block_t block, dispatch_queue_t queue,dispatch_block_t notification_block);
具体使用的方法:
dispatch_queue_t queue &＃61; dispatch_queue_create("queue", DISPATCH_QUEUE_SERIAL);dispatch_block_t previousBlock &＃61; dispatch_block_create(0, ^{NSLog(&＃64;"previousBlock begin");[NSThread sleepForTimeInterval:1];NSLog(&＃64;"previousBlock done");});dispatch_async(queue, previousBlock);dispatch_block_t notifyBlock &＃61; dispatch_block_create(0, ^{NSLog(&＃64;"notifyBlock");});//当previousBlock执行完毕后&＃xff0c;提交notifyBlock到global queue中执行dispatch_block_notify(previousBlock, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), notifyBlock);
运行结果&＃xff1a;
GCDTests[17129:895673] previousBlock beginGCDTests[17129:895673] previousBlock doneGCDTests[17129:895673] notifyBlock
dispatch_queue_t queue &＃61; dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);dispatch_group_t group &＃61; dispatch_group_create();//将任务异步地添加到group中去执行dispatch_group_async(group,queue,^{ NSLog(&＃64;"block1"); });dispatch_group_async(group,queue,^{ NSLog(&＃64;"block2"); });dispatch_group_wait(group,DISPATCH_TIME_FOREVER);NSLog(&＃64;"go on");
执行结果如下&＃xff0c;只有block1跟block2执行完毕后才会执行dispatch_group_wait后面的内容。
GCDTests[954:41031] block2GCDTests[954:41032] block1GCDTests[954:40847] go on
void dispatch_group_notify(dispatch_group_t group, //要观察的groupdispatch_queue_t queue, //block执行的队列dispatch_block_t block); //当group中所有任务执行完毕之后要执行的block
简单的示意用法:
dispatch_queue_t queue &＃61; dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);dispatch_group_t group &＃61; dispatch_group_create();dispatch_group_async(group,queue,^{ NSLog(&＃64;"block1"); });dispatch_group_async(group,queue,^{ NSLog(&＃64;"block2"); });dispatch_group_notify(group, dispatch_get_main_queue(), ^{NSLog(&＃64;"done");});NSLog(&＃64;"go on");
可以看到如下的执行结果
GCDTests[1046:45104] go onGCDTests[1046:45153] block1GCDTests[1046:45152] block2GCDTests[1046:45104] done
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