iOS多線(xiàn)程：GCD

1.GCD的概念

GCD為Grand Central Dispatch的縮寫(xiě)脆丁。
它主要用于優(yōu)化應(yīng)用程序以支持多核處理器以及其他對(duì)稱(chēng)多處理系統(tǒng)句喷。它是一個(gè)在線(xiàn)程池模式的基礎(chǔ)上執(zhí)行的并行任務(wù)丐膝。在Mac OS X 10.6雪豹中首次推出鞍历，也可在IOS 4及以上版本使用。

2.GCD的隊(duì)列和任務(wù)

GCD包括兩個(gè)核心概念：隊(duì)列和任務(wù)

2.1隊(duì)列

隊(duì)列是一種特殊的線(xiàn)性表跨算，遵循FIFO（先進(jìn)先出）原則轻要，新添加的任務(wù)在隊(duì)尾，執(zhí)行任務(wù)的時(shí)候從隊(duì)首開(kāi)始讀取并執(zhí)行旱爆。隊(duì)列分為串行隊(duì)列和并行隊(duì)列舀射，區(qū)別主要是：隊(duì)列中任務(wù)執(zhí)行的順序不同，開(kāi)啟的線(xiàn)程數(shù)也不同怀伦。

串行隊(duì)列

每個(gè)時(shí)間段只有一個(gè)任務(wù)在執(zhí)行脆烟，只開(kāi)啟一個(gè)線(xiàn)程，一個(gè)任務(wù)執(zhí)行完以后再執(zhí)行下一個(gè)任務(wù)房待。

并行隊(duì)列

可以有多個(gè)任務(wù)在并發(fā)執(zhí)行邢羔，可以開(kāi)啟多個(gè)線(xiàn)程同時(shí)處理多個(gè)任務(wù)。

2.2任務(wù)

任務(wù)就是需要執(zhí)行的一組操作桑孩，在GCD是放在block中的那一段代碼拜鹤，任務(wù)分為同步任務(wù)和異步任務(wù)，區(qū)別是：是否等待隊(duì)列的任務(wù)執(zhí)行結(jié)束流椒，以及是否具備開(kāi)啟新線(xiàn)程的能力敏簿。

同步sync

同步任務(wù)會(huì)等待操作執(zhí)行完畢，再執(zhí)行block外的操作镣隶，只能在當(dāng)前線(xiàn)程中執(zhí)行任務(wù)极谊。

異步async

異步任務(wù)不會(huì)等待操作執(zhí)行完畢，會(huì)直接繼續(xù)執(zhí)行block外的操作安岂，可以在開(kāi)啟新的線(xiàn)程執(zhí)行任務(wù)。

3.GCD的具體使用

3.1創(chuàng)建隊(duì)列

dispatch_queue_t serial_queue = dispatch_queue_create("serial_queue", DISPATCH_QUEUE_SERIAL);
dispatch_queue_t concurrent_queue = dispatch_queue_create("concurrent_queue", DISPATCH_QUEUE_CONCURRENT);

3.2隊(duì)列和任務(wù)的簡(jiǎn)單組合

3.2.1串行+同步

//    串行隊(duì)列+同步
    NSLog(@"主流程start--%@", [NSThread currentThread]);
    dispatch_sync(serial_queue, ^{
        NSLog(@"同步1--操作1--%@", [NSThread currentThread]);
        sleep(3);
        NSLog(@"同步1--操作2--%@", [NSThread currentThread]);
    });
    dispatch_sync(serial_queue, ^{
        NSLog(@"同步2--操作1--%@", [NSThread currentThread]);
        sleep(1);
        NSLog(@"同步2--操作2--%@", [NSThread currentThread]);
    });
    dispatch_sync(serial_queue, ^{
        NSLog(@"同步3--操作1--%@", [NSThread currentThread]);
        sleep(2);
        NSLog(@"同步3--操作2--%@", [NSThread currentThread]);
    });
    NSLog(@"主流程end-----%@", [NSThread currentThread]);

2021-03-20 17:08:38.693421+0800 test1[8934:9017257] 主流程start--<NSThread: 0x60000102dd80>{number = 1, name = main}
2021-03-20 17:08:38.693566+0800 test1[8934:9017257] 同步1--操作1--<NSThread: 0x60000102dd80>{number = 1, name = main}
2021-03-20 17:08:41.694375+0800 test1[8934:9017257] 同步1--操作2--<NSThread: 0x60000102dd80>{number = 1, name = main}
2021-03-20 17:08:41.694603+0800 test1[8934:9017257] 同步2--操作1--<NSThread: 0x60000102dd80>{number = 1, name = main}
2021-03-20 17:08:42.695118+0800 test1[8934:9017257] 同步2--操作2--<NSThread: 0x60000102dd80>{number = 1, name = main}
2021-03-20 17:08:42.695589+0800 test1[8934:9017257] 同步3--操作1--<NSThread: 0x60000102dd80>{number = 1, name = main}
2021-03-20 17:08:44.696285+0800 test1[8934:9017257] 同步3--操作2--<NSThread: 0x60000102dd80>{number = 1, name = main}
2021-03-20 17:08:44.696645+0800 test1[8934:9017257] 主流程end-----<NSThread: 0x60000102dd80>{number = 1, name = main}

3.2.2并行+同步

//    并行隊(duì)列+同步
    NSLog(@"主流程start--%@", [NSThread currentThread]);
    dispatch_sync(concurrent_queue, ^{
        NSLog(@"同步1--操作1--%@", [NSThread currentThread]);
        sleep(3);
        NSLog(@"同步1--操作2--%@", [NSThread currentThread]);
    });
    dispatch_sync(concurrent_queue, ^{
        NSLog(@"同步2--操作1--%@", [NSThread currentThread]);
        sleep(1);
        NSLog(@"同步2--操作2--%@", [NSThread currentThread]);
    });
    dispatch_sync(concurrent_queue, ^{
        NSLog(@"同步3--操作1--%@", [NSThread currentThread]);
        sleep(2);
        NSLog(@"同步3--操作2--%@", [NSThread currentThread]);
    });
    NSLog(@"主流程end-----%@", [NSThread currentThread]);

2021-03-20 17:07:19.312244+0800 test1[8866:9015712] 主流程start--<NSThread: 0x600002961dc0>{number = 1, name = main}
2021-03-20 17:07:19.312456+0800 test1[8866:9015712] 同步1--操作1--<NSThread: 0x600002961dc0>{number = 1, name = main}
2021-03-20 17:07:22.313735+0800 test1[8866:9015712] 同步1--操作2--<NSThread: 0x600002961dc0>{number = 1, name = main}
2021-03-20 17:07:22.314070+0800 test1[8866:9015712] 同步2--操作1--<NSThread: 0x600002961dc0>{number = 1, name = main}
2021-03-20 17:07:23.315434+0800 test1[8866:9015712] 同步2--操作2--<NSThread: 0x600002961dc0>{number = 1, name = main}
2021-03-20 17:07:23.315738+0800 test1[8866:9015712] 同步3--操作1--<NSThread: 0x600002961dc0>{number = 1, name = main}
2021-03-20 17:07:25.317084+0800 test1[8866:9015712] 同步3--操作2--<NSThread: 0x600002961dc0>{number = 1, name = main}
2021-03-20 17:07:25.317458+0800 test1[8866:9015712] 主流程end-----<NSThread: 0x600002961dc0>{number = 1, name = main}

3.2.3串行+異步

//    串行隊(duì)列+異步
       NSLog(@"主流恒start--%@", [NSThread currentThread]);
    dispatch_async(serial_queue, ^{
        NSLog(@"異步1--操作1--%@", [NSThread currentThread]);
        sleep(3);
        NSLog(@"異步1--操作2--%@", [NSThread currentThread]);
    });
    dispatch_async(serial_queue, ^{
        NSLog(@"異步2--操作1--%@", [NSThread currentThread]);
        sleep(1);
        NSLog(@"異步2--操作2--%@", [NSThread currentThread]);
    });
    dispatch_async(serial_queue, ^{
        NSLog(@"異步3--操作1--%@", [NSThread currentThread]);
        sleep(2);
        NSLog(@"異步3--操作2--%@", [NSThread currentThread]);
    });
    NSLog(@"主流程end-----%@", [NSThread currentThread]);

2021-03-20 16:52:39.159286+0800 test1[8200:9002593] 主流恒start--<NSThread: 0x600002b2ab80>{number = 1, name = main}
2021-03-20 16:52:39.159443+0800 test1[8200:9002593] 主流程end-----<NSThread: 0x600002b2ab80>{number = 1, name = main}
2021-03-20 16:52:39.159462+0800 test1[8200:9002672] 異步1--操作1--<NSThread: 0x600002b42040>{number = 6, name = (null)}
2021-03-20 16:52:42.164330+0800 test1[8200:9002672] 異步1--操作2--<NSThread: 0x600002b42040>{number = 6, name = (null)}
2021-03-20 16:52:42.164759+0800 test1[8200:9002672] 異步2--操作1--<NSThread: 0x600002b42040>{number = 6, name = (null)}
2021-03-20 16:52:43.166518+0800 test1[8200:9002672] 異步2--操作2--<NSThread: 0x600002b42040>{number = 6, name = (null)}
2021-03-20 16:52:43.166932+0800 test1[8200:9002672] 異步3--操作1--<NSThread: 0x600002b42040>{number = 6, name = (null)}
2021-03-20 16:52:45.173185+0800 test1[8200:9002672] 異步3--操作2--<NSThread: 0x600002b42040>{number = 6, name = (null)}

image.png

3.2.4并行+異步

NSLog(@"主流恒start--%@", [NSThread currentThread]);
    dispatch_async(concurrent_queue, ^{
        NSLog(@"異步1--操作1--%@", [NSThread currentThread]);
        sleep(3);
        NSLog(@"異步1--操作2--%@", [NSThread currentThread]);
    });
    dispatch_async(concurrent_queue, ^{
        NSLog(@"異步2--操作1--%@", [NSThread currentThread]);
        sleep(1);
        NSLog(@"異步2--操作2--%@", [NSThread currentThread]);
    });
    dispatch_async(concurrent_queue, ^{
        NSLog(@"異步3--操作1--%@", [NSThread currentThread]);
        sleep(2);
        NSLog(@"異步3--操作2--%@", [NSThread currentThread]);
    });
    NSLog(@"主流程end-----%@", [NSThread currentThread]);

2021-03-20 16:44:46.396510+0800 test1[7871:8996717] 主流恒start--<NSThread: 0x600000b8dd80>{number = 1, name = main}
2021-03-20 16:44:46.396648+0800 test1[7871:8996717] 主流程end-----<NSThread: 0x600000b8dd80>{number = 1, name = main}
2021-03-20 16:44:46.396687+0800 test1[7871:8996802] 異步1--操作1--<NSThread: 0x600000be8080>{number = 3, name = (null)}
2021-03-20 16:44:46.396702+0800 test1[7871:8996806] 異步2--操作1--<NSThread: 0x600000b9c900>{number = 5, name = (null)}
2021-03-20 16:44:46.396707+0800 test1[7871:8996803] 異步3--操作1--<NSThread: 0x600000bb9f40>{number = 4, name = (null)}
2021-03-20 16:44:47.398008+0800 test1[7871:8996806] 異步2--操作2--<NSThread: 0x600000b9c900>{number = 5, name = (null)}
2021-03-20 16:44:48.397575+0800 test1[7871:8996803] 異步3--操作2--<NSThread: 0x600000bb9f40>{number = 4, name = (null)}
2021-03-20 16:44:49.398078+0800 test1[7871:8996802] 異步1--操作2--<NSThread: 0x600000be8080>{number = 3, name = (null)}

image.png

結(jié)論

1.對(duì)于同步執(zhí)行的任務(wù)帆吻，不管是放在并行隊(duì)列還是串行隊(duì)列中域那，都是按順序執(zhí)行，且當(dāng)上一個(gè)任務(wù)完成以后才執(zhí)行下一個(gè)任務(wù)猜煮。
2.異步執(zhí)行的任務(wù)次员，串行隊(duì)列會(huì)開(kāi)啟一個(gè)新線(xiàn)程，串行執(zhí)行任務(wù)王带，并行隊(duì)列會(huì)開(kāi)啟多個(gè)新線(xiàn)程淑蔚，并行執(zhí)行任務(wù)。

image.png

3.3死鎖

//  串行隊(duì)列
    dispatch_queue_t queue = dispatch_queue_create("cooci", DISPATCH_QUEUE_SERIAL);
    NSLog(@"1");
    // 異步函數(shù)
    dispatch_async(queue, ^{
        NSLog(@"2");
        dispatch_sync(queue, ^{
            NSLog(@"3");
        });
        NSLog(@"4");
    });
    NSLog(@"5");

image.png

結(jié)果：輸出1愕撰、5刹衫、2以后產(chǎn)生死鎖崩潰
造成死鎖的原因：輸出2以后醋寝，將輸出3的這個(gè)同步函數(shù)（紅框部分）添加到同步隊(duì)列，那么如果要執(zhí)行紅框部分的代碼带迟，按照隊(duì)列先進(jìn)先出的規(guī)則音羞，則需要先執(zhí)行完排在前面的異步函數(shù)（綠框部分），但是該異步函數(shù)又需等待紅框部分執(zhí)行完以后仓犬，產(chǎn)生死鎖嗅绰。
結(jié)論：在串行隊(duì)列中添加同步任務(wù)時(shí)，注意線(xiàn)程阻塞的問(wèn)題搀继，iOS主隊(duì)列是串行隊(duì)列窘面，如果在主線(xiàn)程執(zhí)行過(guò)程中向主隊(duì)列中添加同步操作時(shí)也會(huì)產(chǎn)生死鎖，另外開(kāi)辟一個(gè)線(xiàn)程向主隊(duì)列添加同步操作則不會(huì)產(chǎn)生死鎖叽躯。

例如在viewDidLoad函數(shù)中調(diào)用serialQueueProblem會(huì)在輸出1以后產(chǎn)生死鎖崩潰财边。

- (void)serialQueueProblem{
    NSLog(@"1");
    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"2");
    });
    NSLog(@"3");
}

如果調(diào)用方式換成這樣則正常輸出123

[NSThread detachNewThreadSelector:@selector(serialQueueProblem) toTarget:self withObject:nil];

3.4其他用法

3.4.1 dispatch_once

- (void)dispatchOnce{
    static dispatch_once_t onceToken;
    NSLog(@"%ld", onceToken);
    dispatch_once(&onceToken, ^{
//        只會(huì)執(zhí)行一次
        NSLog(@"1%@", [NSThread currentThread]);
    });
}

調(diào)用三次的執(zhí)行結(jié)果

2021-03-21 18:17:02.376201+0800 test1[67067:9754075] 0
2021-03-21 18:17:02.376363+0800 test1[67067:9754075] 1<NSThread: 0x600002d85e40>{number = 1, name = main}
2021-03-21 18:17:02.376480+0800 test1[67067:9754075] -1
2021-03-21 18:17:02.376559+0800 test1[67067:9754075] -1

常用于實(shí)現(xiàn)一個(gè)單例

+ (instancetype)sharedInstance {
    static XXObject *_instance;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [[XXObject alloc] init];
    });
    return _instance;
}

3.4.2 dispatch_after

多長(zhǎng)時(shí)間之后將任務(wù)添加到隊(duì)列中，所以任務(wù)并不是精準(zhǔn)的三秒之后再執(zhí)行
第一個(gè)參數(shù)：dispatch_time_t類(lèi)型险毁，用于指定延遲時(shí)間
第二個(gè)參數(shù)：指定要追加處理的隊(duì)列
第三個(gè)參數(shù)：指定要執(zhí)行的任務(wù)Block

- (void)dispatchAfter{
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        NSLog(@"1%@", [NSThread currentThread]);
    });
    NSLog(@"2%@", [NSThread currentThread]);
}

2021-03-21 18:21:35.749123+0800 test1[67266:9757808] 2<NSThread: 0x60000057d0c0>{number = 1, name = main}
2021-03-21 18:21:39.037124+0800 test1[67266:9757808] 1<NSThread: 0x60000057d0c0>{number = 1, name = main}

3.4.3 Dispatch Source

Dispatch Source的種類(lèi)：
1制圈、DISPATCH_SOURCE_TYPE_DATA_ADD 變量增加
2、DISPATCH_SOURCE_TYPE_DATA_OR 變量 OR
3畔况、DISPATCH_SOURCE_TYPE_MACH_SEND MACH端口發(fā)送
4鲸鹦、DISPATCH_SOURCE_TYPE_MACH_RECV MACH端口接收
5、DISPATCH_SOURCE_TYPE_MEMORYPRESSURE 內(nèi)存壓力 (注：iOS8后可用)
6跷跪、DISPATCH_SOURCE_TYPE_PROC 檢測(cè)到與進(jìn)程相關(guān)的事件
7馋嗜、DISPATCH_SOURCE_TYPE_READ 可讀取文件映像
8、DISPATCH_SOURCE_TYPE_SIGNAL 接收信號(hào)
9吵瞻、DISPATCH_SOURCE_TYPE_TIMER 定時(shí)器
10葛菇、DISPATCH_SOURCE_TYPE_VNODE 文件系統(tǒng)有變更
11、DISPATCH_SOURCE_TYPE_WRITE 可寫(xiě)入文件映像

使用DISPATCH_SOURCE_TYPE_TIMER可以實(shí)現(xiàn)一個(gè)每三秒執(zhí)行一次的定時(shí)器

- (void)dispatchSource{
    _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
    dispatch_source_set_timer(_timer, DISPATCH_TIME_NOW, 3 * NSEC_PER_SEC, 0);
    dispatch_source_set_event_handler(_timer, ^{
        NSLog(@"1%@", [NSThread currentThread]);
    });
    NSLog(@"2%@", [NSThread currentThread]);
    dispatch_resume(_timer);
    NSLog(@"3%@", [NSThread currentThread]);
}

2021-03-21 18:39:52.466493+0800 test1[68104:9773071] 2<NSThread: 0x600000c492c0>{number = 1, name = main}
2021-03-21 18:39:52.466664+0800 test1[68104:9773071] 3<NSThread: 0x600000c492c0>{number = 1, name = main}
2021-03-21 18:39:52.476591+0800 test1[68104:9773071] 1<NSThread: 0x600000c492c0>{number = 1, name = main}
2021-03-21 18:39:55.467553+0800 test1[68104:9773071] 1<NSThread: 0x600000c492c0>{number = 1, name = main}
2021-03-21 18:39:58.467371+0800 test1[68104:9773071] 1<NSThread: 0x600000c492c0>{number = 1, name = main}
2021-03-21 18:40:01.467143+0800 test1[68104:9773071] 1<NSThread: 0x600000c492c0>{number = 1, name = main}

3.4.4 dispatch_apply

按指定的次數(shù)將指定的Block追加到指定的Dispatch Queue中橡羞，并等待全部處理執(zhí)行結(jié)束眯停，用在并行隊(duì)列執(zhí)行順序無(wú)序，用在串行隊(duì)列則按順序執(zhí)行

- (void)dispatchApply{
    dispatch_queue_t queue1 = dispatch_queue_create("aaa", DISPATCH_QUEUE_CONCURRENT);
    dispatch_queue_t queue2 = dispatch_queue_create("aaa", DISPATCH_QUEUE_SERIAL);
    dispatch_apply(5, queue1, ^(size_t index) {
        NSLog(@"并行隊(duì)列%ld%@", index, [NSThread mainThread]);
    });
    NSLog(@"并行結(jié)束-----");
    dispatch_apply(5, queue2, ^(size_t index) {
        NSLog(@"串行隊(duì)列%ld%@", index, [NSThread mainThread]);
    });
    NSLog(@"串行結(jié)束-----");
}

2021-03-21 18:55:42.463961+0800 test1[68871:9787727] 并行隊(duì)列3<NSThread: 0x600002c34380>{number = 1, name = (null)}
2021-03-21 18:55:42.463966+0800 test1[68871:9787725] 并行隊(duì)列1<NSThread: 0x600002c34380>{number = 1, name = (null)}
2021-03-21 18:55:42.463966+0800 test1[68871:9787728] 并行隊(duì)列2<NSThread: 0x600002c34380>{number = 1, name = (null)}
2021-03-21 18:55:42.464026+0800 test1[68871:9787730] 并行隊(duì)列4<NSThread: 0x600002c34380>{number = 1, name = (null)}
2021-03-21 18:55:42.463961+0800 test1[68871:9787529] 并行隊(duì)列0<NSThread: 0x600002c34380>{number = 1, name = main}
2021-03-21 18:55:42.464151+0800 test1[68871:9787529] 并行結(jié)束-----
2021-03-21 18:55:42.464242+0800 test1[68871:9787529] 串行隊(duì)列0<NSThread: 0x600002c34380>{number = 1, name = main}
2021-03-21 18:55:42.464341+0800 test1[68871:9787529] 串行隊(duì)列1<NSThread: 0x600002c34380>{number = 1, name = main}
2021-03-21 18:55:42.464434+0800 test1[68871:9787529] 串行隊(duì)列2<NSThread: 0x600002c34380>{number = 1, name = main}
2021-03-21 18:55:42.464674+0800 test1[68871:9787529] 串行隊(duì)列3<NSThread: 0x600002c34380>{number = 1, name = main}
2021-03-21 18:55:42.464891+0800 test1[68871:9787529] 串行隊(duì)列4<NSThread: 0x600002c34380>{number = 1, name = main}
2021-03-21 18:55:42.465079+0800 test1[68871:9787529] 串行結(jié)束-----

3.4.5 dispatch_barrier

柵欄函數(shù)之前的任務(wù)執(zhí)行完以后卿泽，并且柵欄函數(shù)執(zhí)行完莺债，才執(zhí)行后面的操作
串行隊(duì)列或者系統(tǒng)提供的全局并發(fā)隊(duì)列,這個(gè)柵欄函數(shù)的作用等同于一個(gè)同步函數(shù)的作用
dispatch_barrier_sync和dispatch_barrier_async的區(qū)別是，在當(dāng)前線(xiàn)程中的操作签夭，是否需要等待自己執(zhí)行完再執(zhí)行

- (void)dispatchBarrier{
    dispatch_queue_t queue = dispatch_queue_create("bbb", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        sleep(2);
        NSLog(@"1%@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        sleep(1);
        NSLog(@"2%@", [NSThread currentThread]);
    });
    dispatch_barrier_sync(queue, ^{
        sleep(1);
        NSLog(@"barrier%@", [NSThread currentThread]);
    });
    NSLog(@"barrier done");
    dispatch_async(queue, ^{
        sleep(2);
        NSLog(@"3%@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        sleep(1);
        NSLog(@"4%@", [NSThread currentThread]);
    });
}

2021-03-21 19:11:09.974409+0800 test1[69598:9801166] 2<NSThread: 0x600000850640>{number = 6, name = (null)}
2021-03-21 19:11:10.974576+0800 test1[69598:9801168] 1<NSThread: 0x600000850600>{number = 4, name = (null)}
2021-03-21 19:11:11.975488+0800 test1[69598:9801093] barrier<NSThread: 0x6000008220c0>{number = 1, name = main}
2021-03-21 19:11:11.975850+0800 test1[69598:9801093] barrier done
2021-03-21 19:11:12.980667+0800 test1[69598:9801166] 4<NSThread: 0x600000850640>{number = 6, name = (null)}
2021-03-21 19:11:13.977532+0800 test1[69598:9801168] 3<NSThread: 0x600000850600>{number = 4, name = (null)}

如果把dispatch_barrier_sync換成dispatch_barrier_async

2021-03-21 19:12:25.502966+0800 test1[69660:9802632] barrier done
2021-03-21 19:12:26.503388+0800 test1[69660:9802717] 2<NSThread: 0x600001504280>{number = 6, name = (null)}
2021-03-21 19:12:27.507601+0800 test1[69660:9802728] 1<NSThread: 0x6000015823c0>{number = 3, name = (null)}
2021-03-21 19:12:28.511868+0800 test1[69660:9802728] barrier<NSThread: 0x6000015823c0>{number = 3, name = (null)}
2021-03-21 19:12:29.514776+0800 test1[69660:9802718] 4<NSThread: 0x600001581bc0>{number = 4, name = (null)}
2021-03-21 19:12:30.515791+0800 test1[69660:9802728] 3<NSThread: 0x6000015823c0>{number = 3, name = (null)}

3.5 diapatch_group

將要并發(fā)執(zhí)行的多個(gè)任務(wù)合并為一組齐邦，這樣調(diào)用者就可以知道這些任務(wù)何時(shí)能全部執(zhí)行完

3.5.1 新建group

dispatch_group_t group = dispatch_group_create();

3.5.2 將任務(wù)添加到group

用法一：dispatch_group_async

- (void)dispatchGroup1{
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_queue_create("aaa", DISPATCH_QUEUE_CONCURRENT);
    dispatch_group_async(group, queue, ^{
        sleep(2);
        NSLog(@"1%@", [NSThread currentThread]);
    });
    dispatch_group_async(group, queue, ^{
        sleep(1);
        NSLog(@"2%@", [NSThread currentThread]);
    });
    dispatch_group_notify(group, queue, ^{
        NSLog(@"notify%@", [NSThread currentThread]);
    });
    dispatch_group_async(group, queue, ^{
        sleep(1);
        NSLog(@"3%@", [NSThread currentThread]);
    });
}

2021-03-21 20:28:06.280832+0800 test1[72687:9846592] 2<NSThread: 0x600001854a00>{number = 4, name = (null)}
2021-03-21 20:28:06.280833+0800 test1[72687:9846593] 3<NSThread: 0x60000183a7c0>{number = 3, name = (null)}
2021-03-21 20:28:07.279869+0800 test1[72687:9846591] 1<NSThread: 0x60000184e300>{number = 7, name = (null)}
2021-03-21 20:28:07.280195+0800 test1[72687:9846591] notify<NSThread: 0x60000184e300>{number = 7, name = (null)}

用法二：dispatch_group_enter+dispatch_group_leave配對(duì)使用

- (void)dispatchGroup2{
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_queue_create("111", DISPATCH_QUEUE_CONCURRENT);
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        sleep(2);
        NSLog(@"1%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        sleep(1);
        NSLog(@"2%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });
    dispatch_group_notify(group, queue, ^{
        NSLog(@"notify%@", [NSThread currentThread]);
    });
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        sleep(1);
        NSLog(@"3%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });
}

2021-03-21 20:44:53.567884+0800 test1[73477:9862570] 2<NSThread: 0x6000024a04c0>{number = 5, name = (null)}
2021-03-21 20:44:53.567930+0800 test1[73477:9862573] 3<NSThread: 0x6000024946c0>{number = 3, name = (null)}
2021-03-21 20:44:54.567761+0800 test1[73477:9862572] 1<NSThread: 0x6000024bf380>{number = 6, name = (null)}
2021-03-21 20:44:54.568120+0800 test1[73477:9862572] notify<NSThread: 0x6000024bf380>{number = 6, name = (null)}

3.5.3 監(jiān)聽(tīng)group里面的任務(wù)是否都完成

方法一：dispatch_group_notify使用方法如3.5.2
方法二：dispatch_group_wait設(shè)置等待時(shí)間，在等待時(shí)間結(jié)束后第租，如果還沒(méi)有執(zhí)行完任務(wù)組措拇，則返回。返回0代表執(zhí)行成功慎宾，非0則執(zhí)行失敗

- (void)dispatchGroupWait{
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_queue_create("aaa", DISPATCH_QUEUE_CONCURRENT);
    dispatch_group_async(group, queue, ^{
        sleep(2);
        NSLog(@"1%@", [NSThread currentThread]);
    });
    dispatch_group_async(group, queue, ^{
        sleep(1);
        NSLog(@"2%@", [NSThread currentThread]);
    });
    dispatch_group_async(group, queue, ^{
        sleep(1);
        NSLog(@"3%@", [NSThread currentThread]);
    });
    long ret = dispatch_group_wait(group, dispatch_time(DISPATCH_TIME_NOW, (int64_t)(4 * NSEC_PER_SEC)));
    NSLog(@"ret = %ld", ret);
}

2021-03-21 20:57:35.552239+0800 test1[74073:9874594] 2<NSThread: 0x60000376c500>{number = 5, name = (null)}
2021-03-21 20:57:35.552252+0800 test1[74073:9874597] 3<NSThread: 0x60000376e540>{number = 3, name = (null)}
2021-03-21 20:57:36.552133+0800 test1[74073:9874595] 1<NSThread: 0x600003738780>{number = 4, name = (null)}
2021-03-21 20:57:36.552526+0800 test1[74073:9874485] ret = 0

如果把dispatch_group_wait的等待時(shí)長(zhǎng)減少到1秒則返回非0

3.6 信號(hào)量 dispatch_semaphore

dispatch_semaphore_create(long value);創(chuàng)建信號(hào)量丐吓，參數(shù)為設(shè)置信號(hào)量的初始值
dispatch_semaphore_signal(dispatch_semaphore_t dsema);發(fā)送信號(hào)量浅悉，信號(hào)量的值+1
dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout);等待信號(hào)量，第一個(gè)為當(dāng)前等待的信號(hào)量汰蜘，第二個(gè)參數(shù)為超時(shí)時(shí)間仇冯。在信號(hào)量≤0的時(shí)候會(huì)一直等待，直到超時(shí)族操，并且會(huì)阻塞該線(xiàn)程苛坚，當(dāng)信號(hào)量>0時(shí)會(huì)繼續(xù)執(zhí)行，信號(hào)量-1色难。

使用信號(hào)量控制最大并發(fā)數(shù)

- (void)dispatchSemaphore{
    dispatch_group_t group = dispatch_group_create();
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(3);
    dispatch_queue_t queue = dispatch_queue_create("qqq", DISPATCH_QUEUE_CONCURRENT);
    for (int i = 0; i < 10; i ++) {
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        dispatch_group_async(group, queue, ^{
            sleep(1);
            NSLog(@"%d%@", i, [NSThread currentThread]);
            dispatch_semaphore_signal(semaphore);
        });
    }
    dispatch_group_notify(group, queue, ^{
        NSLog(@"done");
    });
}

最后編輯于：2021.03.21 21:51:07

?著作權(quán)歸作者所有,轉(zhuǎn)載或內(nèi)容合作請(qǐng)聯(lián)系作者

人面猴
序言：七十年代末泼舱，一起剝皮案震驚了整個(gè)濱河市，隨后出現(xiàn)的幾起案子枷莉，更是在濱河造成了極大的恐慌娇昙，老刑警劉巖，帶你破解...
沈念sama閱讀 218,122評(píng)論 6贊 505
死咒
序言：濱河連續(xù)發(fā)生了三起死亡事件笤妙，死亡現(xiàn)場(chǎng)離奇詭異冒掌，居然都是意外死亡，警方通過(guò)查閱死者的電腦和手機(jī)蹲盘，發(fā)現(xiàn)死者居然都...
沈念sama閱讀 93,070評(píng)論 3贊 395
救了他兩次的神仙讓他今天三更去死
文/潘曉璐我一進(jìn)店門(mén)股毫，熙熙樓的掌柜王于貴愁眉苦臉地迎上來(lái)，“玉大人召衔，你說(shuō)我怎么就攤上這事铃诬。” “怎么了苍凛？”我有些...
開(kāi)封第一講書(shū)人閱讀 164,491評(píng)論 0贊 354
道士緝兇錄：失蹤的賣(mài)姜人
文/不壞的土叔我叫張陵趣席，是天一觀(guān)的道長(zhǎng)。經(jīng)常有香客問(wèn)我醇蝴，道長(zhǎng)宣肚，這世上最難降的妖魔是什么？我笑而不...
開(kāi)封第一講書(shū)人閱讀 58,636評(píng)論 1贊 293
?港島之戀（遺憾婚禮）
正文為了忘掉前任悠栓，我火速辦了婚禮钉寝，結(jié)果婚禮上，老公的妹妹穿的比我還像新娘闸迷。我一直安慰自己，他們只是感情好俘枫，可當(dāng)我...
茶點(diǎn)故事閱讀 67,676評(píng)論 6贊 392
惡毒庶女頂嫁案：這布局不是一般人想出來(lái)的
文/花漫我一把揭開(kāi)白布腥沽。她就那樣靜靜地躺著，像睡著了一般鸠蚪。火紅的嫁衣襯著肌膚如雪今阳。梳的紋絲不亂的頭發(fā)上师溅，一...
開(kāi)封第一講書(shū)人閱讀 51,541評(píng)論 1贊 305
城市分裂傳說(shuō)
那天，我揣著相機(jī)與錄音盾舌，去河邊找鬼墓臭。笑死，一個(gè)胖子當(dāng)著我的面吹牛妖谴，可吹牛的內(nèi)容都是我干的窿锉。我是一名探鬼主播，決...
沈念sama閱讀 40,292評(píng)論 3贊 418
雙鴛鴦連環(huán)套：你想象不到人心有多黑
文/蒼蘭香墨我猛地睜開(kāi)眼膝舅，長(zhǎng)吁一口氣：“原來(lái)是場(chǎng)噩夢(mèng)啊……” “哼嗡载！你這毒婦竟也來(lái)了？” 一聲冷哼從身側(cè)響起仍稀，我...
開(kāi)封第一講書(shū)人閱讀 39,211評(píng)論 0贊 276
萬(wàn)榮殺人案實(shí)錄
序言：老撾萬(wàn)榮一對(duì)情侶失蹤洼滚，失蹤者是張志新（化名）和其女友劉穎，沒(méi)想到半個(gè)月后技潘，有當(dāng)?shù)厝嗽跇?shù)林里發(fā)現(xiàn)了一具尸體遥巴，經(jīng)...
沈念sama閱讀 45,655評(píng)論 1贊 314
?護(hù)林員之死
正文獨(dú)居荒郊野嶺守林人離奇死亡，尸身上長(zhǎng)有42處帶血的膿包…… 初始之章·張勛以下內(nèi)容為張勛視角年9月15日...
茶點(diǎn)故事閱讀 37,846評(píng)論 3贊 336
?白月光啟示錄
正文我和宋清朗相戀三年享幽，在試婚紗的時(shí)候發(fā)現(xiàn)自己被綠了铲掐。大學(xué)時(shí)的朋友給我發(fā)了我未婚夫和他白月光在一起吃飯的照片。...
茶點(diǎn)故事閱讀 39,965評(píng)論 1贊 348
活死人
序言：一個(gè)原本活蹦亂跳的男人離奇死亡琉闪，死狀恐怖迹炼，靈堂內(nèi)的尸體忽然破棺而出，到底是詐尸還是另有隱情颠毙，我是刑警寧澤斯入，帶...
沈念sama閱讀 35,684評(píng)論 5贊 347
?日本核電站爆炸內(nèi)幕
正文年R本政府宣布，位于F島的核電站蛀蜜，受9級(jí)特大地震影響刻两，放射性物質(zhì)發(fā)生泄漏。R本人自食惡果不足惜滴某，卻給世界環(huán)境...
茶點(diǎn)故事閱讀 41,295評(píng)論 3贊 329
男人毒藥：我在死后第九天來(lái)索命
文/蒙蒙一磅摹、第九天我趴在偏房一處隱蔽的房頂上張望。院中可真熱鬧霎奢，春花似錦户誓、人聲如沸。這莊子的主人今日做“春日...
開(kāi)封第一講書(shū)人閱讀 31,894評(píng)論 0贊 22
一樁弒父案帝美，背后竟有這般陰謀
文/蒼蘭香墨我抬頭看了看天上的太陽(yáng)。三九已至晤硕，卻和暖如春悼潭，著一層夾襖步出監(jiān)牢的瞬間庇忌，已是汗流浹背。一陣腳步聲響...
開(kāi)封第一講書(shū)人閱讀 33,012評(píng)論 1贊 269
情欲美人皮
我被黑心中介騙來(lái)泰國(guó)打工舰褪，沒(méi)想到剛下飛機(jī)就差點(diǎn)兒被人妖公主榨干…… 1. 我叫王不留皆疹，地道東北人。一個(gè)月前我還...
沈念sama閱讀 48,126評(píng)論 3贊 370
代替公主和親
正文我出身青樓占拍，卻偏偏與公主長(zhǎng)得像略就，于是被迫代替她去往敵國(guó)和親。傳聞我的和親對(duì)象是個(gè)殘疾皇子刷喜，可洞房花燭夜當(dāng)晚...
茶點(diǎn)故事閱讀 44,914評(píng)論 2贊 355

iOS多線(xiàn)程：GCD

1.GCD的概念

2.GCD的隊(duì)列和任務(wù)

2.1隊(duì)列

串行隊(duì)列

并行隊(duì)列

2.2任務(wù)

3.GCD的具體使用

3.1創(chuàng)建隊(duì)列

3.2隊(duì)列和任務(wù)的簡(jiǎn)單組合

3.2.1串行+同步

3.2.2并行+同步

3.2.3串行+異步

3.2.4并行+異步

結(jié)論

3.3死鎖

3.4其他用法

3.4.1 dispatch_once

3.4.2 dispatch_after

3.4.3 Dispatch Source

3.4.4 dispatch_apply

3.5 diapatch_group

3.5.1 新建group

3.5.2 將任務(wù)添加到group

3.5.3 監(jiān)聽(tīng)group里面的任務(wù)是否都完成

3.6 信號(hào)量 dispatch_semaphore

推薦閱讀更多精彩內(nèi)容