本文內(nèi)容
任務(wù)、隊(duì)列的概念匙赞、創(chuàng)建方式
任務(wù) + 隊(duì)列的6種組合的執(zhí)行方式
線程間如何通信
dispatch_once屡穗、dispatch_after、dispatch_apply(快速迭代)悼凑、dispatch_barrier(柵欄函數(shù))偿枕、dispatch_group(隊(duì)列組)、dispatch_semaphore(信號(hào)量)如何實(shí)現(xiàn)線程安全與線程同步
iOS多線程demo地址
上文說(shuō)到iOS 多線程- pThread和NSThread
這篇文章來(lái)講講GCD
GCD ??????????的優(yōu)點(diǎn)
- 可用于多核的并行運(yùn)算
- 會(huì)自動(dòng)利用更多的CPU內(nèi)核
- 自動(dòng)管理線程的生命周期（創(chuàng)建線程户辫、調(diào)度任務(wù)渐夸、銷毀線程）
- 只用關(guān)注執(zhí)行什么任務(wù)，不用編寫任何線程管理代碼
1.任務(wù)
任務(wù)：執(zhí)行的操作渔欢，放在block中的代碼
執(zhí)行任務(wù)的方式有兩種墓塌，主要區(qū)別是：是否等待隊(duì)列中的任務(wù)執(zhí)行結(jié)束，是否具備開啟新線程的能力奥额。
同步執(zhí)行（sync）：同步添加當(dāng)前任務(wù)到指定的隊(duì)列中苫幢，在隊(duì)列中的任務(wù)全部結(jié)束之前，
會(huì)一直等待垫挨，直到隊(duì)列中的任務(wù)全部完成后韩肝，才開始下一個(gè)任務(wù)，只能在當(dāng)前線程中執(zhí)行任務(wù)九榔，不具備開啟線程的能力哀峻。異步執(zhí)行 (async)：異步添加當(dāng)前任務(wù)到指定隊(duì)列中涡相，
不會(huì)等待隊(duì)列的任務(wù)執(zhí)行結(jié)束，直接開始執(zhí)行下一個(gè)任務(wù)剩蟀，可以在新的線程中執(zhí)行任務(wù)催蝗，具備開啟線程的能力。
*注意：異步執(zhí)行 (async)雖然具有開啟線程的能力育特，但是不一定會(huì)開啟新的線程丙号，這跟任務(wù)所指定的隊(duì)列有關(guān)
2.隊(duì)列
隊(duì)列：存放任務(wù)的隊(duì)列，隊(duì)列是一種特殊的線性表缰冤，采用FIFO（先進(jìn)先出）的原則犬缨，即新任務(wù)總是被插入到隊(duì)列末尾，而讀取任務(wù)總是從隊(duì)列的頭部開始讀取锋谐，每讀取一個(gè)任務(wù)遍尺，隊(duì)列中則釋放一個(gè)任務(wù)。
隊(duì)列有兩種方式涮拗，都滿足FIFO原則乾戏，主要區(qū)別是：執(zhí)行順序不同，開啟線程數(shù)不同
- 串行隊(duì)列（Serial Dispatch Queue ）：只開啟
一個(gè)線程三热，一個(gè)任務(wù)執(zhí)行完畢后鼓择，再執(zhí)行下一個(gè)任務(wù) - 并行隊(duì)列（Concurrent Dispatch Queue）?????????????? ??????????????????????????????????????????????????????????????：可以開啟
多個(gè)線程，并且同時(shí)執(zhí)行多個(gè)任務(wù)
3.使用步驟
- 創(chuàng)建一個(gè)隊(duì)列
- 將任務(wù)添加到隊(duì)列中就漾，系統(tǒng)根據(jù)任務(wù)執(zhí)行方式（同步呐能、異步）進(jìn)行執(zhí)行
3.1 隊(duì)列的創(chuàng)建、獲取
使用dispatch_queue_create創(chuàng)建隊(duì)列
第一個(gè)參數(shù)：隊(duì)列的唯一標(biāo)識(shí)符抑堡，用于DEBUG摆出，可以為空，推薦使用應(yīng)用程序ID這種逆序全局域名首妖。
第二個(gè)參數(shù)：隊(duì)列類型偎漫，串行隊(duì)列DISPATCH_QUEUE_SERIAL，并行隊(duì)列DISPATCH_QUEUE_CONCURRENT
//創(chuàng)建串行隊(duì)列
dispatch_queue_t queue = dispatch_queue_create("com.xiuxiu.queque", DISPATCH_QUEUE_SERIAL);
//創(chuàng)建并行隊(duì)列
dispatch_queue_t queue2 = dispatch_queue_create("com.xiuxiu.queque", DISPATCH_QUEUE_CONCURRENT);
主隊(duì)列Main Dispatch Queue: GCD提供一種特殊串行隊(duì)列：
- 所有放在主隊(duì)列中的任務(wù)有缆，都會(huì)放到主線程中執(zhí)行
- 可使用
dispatch_get_main_queue()獲取主隊(duì)列
主隊(duì)列獲取方法
dispatch_queue_t queue = dispatch_get_main_queue()
全局并發(fā)隊(duì)列Global Dispatch Queue ： GCD默認(rèn)提供的全局并發(fā)隊(duì)列
并發(fā)隊(duì)列獲取方法：
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_get_global_queue獲取全局隊(duì)列
第一個(gè)參數(shù)：隊(duì)列的優(yōu)先級(jí)
#define DISPATCH_QUEUE_PRIORITY_HIGH 2
#define DISPATCH_QUEUE_PRIORITY_DEFAULT 0
#define DISPATCH_QUEUE_PRIORITY_LOW (-2)
#define DISPATCH_QUEUE_PRIORITY_BACKGROUND INT16_MIN
第二個(gè)參數(shù)：沒(méi)有使用象踊，用0 即可
3.2 任務(wù)的執(zhí)行方式
dispatch_async(queue, ^{
//異步執(zhí)行任務(wù)代碼
});
dispatch_sync(queue, ^{
//同步執(zhí)行任務(wù)代碼
});
第一個(gè)參數(shù)是隊(duì)列，那么隊(duì)列 + 任務(wù) 執(zhí)行方式就有6種組合（加上主隊(duì)列）
同步執(zhí)行 + 串行隊(duì)列
異步執(zhí)行 + 串行隊(duì)列
同步執(zhí)行 + 并行隊(duì)列
異步執(zhí)行 + 并行隊(duì)列
同步執(zhí)行 + 主隊(duì)列
異步執(zhí)行 + 主隊(duì)列
3.2.1.同步執(zhí)行 + 串行隊(duì)列
/*
同步執(zhí)行 + 串行隊(duì)列
不會(huì)開啟新線程棚壁，在當(dāng)前線程中執(zhí)行任務(wù)杯矩，一個(gè)任務(wù)執(zhí)行完畢后，再執(zhí)行下一個(gè)任務(wù)
*/
- (void)syncSerial{
NSLog(@" syncSerial start");
dispatch_queue_t queue = dispatch_queue_create("com.xiuxiu.syncSerial", DISPATCH_QUEUE_SERIAL);
dispatch_sync(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一袖外，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_sync(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二史隆，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
NSLog(@" syncSerial end");
}
：前面的編號(hào)代表進(jìn)程的編號(hào)，一個(gè)APP的就是一個(gè)進(jìn)程曼验，進(jìn)程編號(hào)總是一致的泌射；
：后面的編號(hào)代表線程的編號(hào)头镊， 21898代表線程的編號(hào)
輸出結(jié)果：
- 在當(dāng)前線程中執(zhí)行任務(wù)，沒(méi)有開啟新線程（同步執(zhí)行不具備開啟線程能力）魄幕，根據(jù)線程編號(hào)看出
- 所有任務(wù)都在
syncSerial start和syncSerial end之間執(zhí)行（同步執(zhí)行需要等待隊(duì)列中的任務(wù)執(zhí)行結(jié)束） - 任務(wù)按順序執(zhí)行（串行隊(duì)列每次只有一個(gè)任務(wù)被執(zhí)行，一個(gè)任務(wù)執(zhí)行完畢后颖杏，再執(zhí)行下一個(gè)任務(wù)）
2018-12-27 10:19:08.371664+0800 Thread[908:21898] syncSerial start
2018-12-27 10:19:08.371980+0800 Thread[908:21898] 任務(wù)一纯陨，i = 0
2018-12-27 10:19:09.372354+0800 Thread[908:21898] 任務(wù)一，i = 1
2018-12-27 10:19:10.372865+0800 Thread[908:21898] 任務(wù)一留储，i = 2
2018-12-27 10:19:11.373588+0800 Thread[908:21898] 任務(wù)二翼抠，i = 0
2018-12-27 10:19:12.374936+0800 Thread[908:21898] 任務(wù)二，i = 1
2018-12-27 10:19:13.375258+0800 Thread[908:21898] 任務(wù)二获讳，i = 2
2018-12-27 10:19:14.376006+0800 Thread[908:21898] syncSerial end
3.2.2.異步執(zhí)行 + 串行隊(duì)列
/*
異步執(zhí)行 + 串行隊(duì)列
會(huì)開啟新線程阴颖，但是因?yàn)殛?duì)列是串行的，一個(gè)任務(wù)執(zhí)行完畢后丐膝，再執(zhí)行下一個(gè)任務(wù)
*/
- (void)asyncSerial{
NSLog(@" asyncSerial start");
dispatch_queue_t queue = dispatch_queue_create("com.xiuxiu.asyncSerial", DISPATCH_QUEUE_SERIAL);
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一量愧，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
NSLog(@" asyncSerial end");
}
輸出結(jié)果：
- 開啟一條線程（異步執(zhí)行具備開啟線程的能力帅矗，因?yàn)槭谴嘘?duì)列偎肃，只開啟了一條線程）
- 所有任務(wù)都在
asyncSerial start和asyncSerial end之后執(zhí)行（異步執(zhí)行不會(huì)等待，繼續(xù)執(zhí)行任務(wù)） - 任務(wù)按順序執(zhí)行（串行隊(duì)列每次只有一個(gè)任務(wù)被執(zhí)行浑此，任務(wù)一個(gè)接著一個(gè)執(zhí)行）
2018-12-27 10:43:17.947620+0800 Thread[1105:32316] asyncSerial start
2018-12-27 10:43:17.947916+0800 Thread[1105:32316] asyncSerial end
2018-12-27 10:43:17.948034+0800 Thread[1105:32360] 任務(wù)一累颂，i = 0
2018-12-27 10:43:18.953286+0800 Thread[1105:32360] 任務(wù)一，i = 1
2018-12-27 10:43:19.956284+0800 Thread[1105:32360] 任務(wù)一凛俱，i = 2
2018-12-27 10:43:20.961804+0800 Thread[1105:32360] 任務(wù)二紊馏，i = 0
2018-12-27 10:43:21.965620+0800 Thread[1105:32360] 任務(wù)二，i = 1
2018-12-27 10:43:22.967181+0800 Thread[1105:32360] 任務(wù)二蒲犬，i = 2
3.2.3. 同步執(zhí)行 + 并行隊(duì)列
/*
同步執(zhí)行 + 并行隊(duì)列
不會(huì)開啟新線程朱监，在當(dāng)前線程中執(zhí)行任務(wù)，一個(gè)任務(wù)執(zhí)行完畢后暖哨，再執(zhí)行下一個(gè)任務(wù)
*/
- (void)syncConcurrent{
NSLog(@" syncConcurrent start");
dispatch_queue_t queue = dispatch_queue_create("com.xiuxiu.syncConcurrent", DISPATCH_QUEUE_CONCURRENT);
dispatch_sync(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一赌朋，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_sync(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
NSLog(@" syncConcurrent end");
}
輸出結(jié)果:
- 在當(dāng)前線程中執(zhí)行任務(wù)篇裁，沒(méi)有開啟新線程（同步執(zhí)行不具備開啟線程能力）沛慢，根據(jù)線程編號(hào)看出，上面講過(guò)
- 所有任務(wù)都在
syncConcurrent start和syncConcurrent end之間執(zhí)行（同步執(zhí)行需要等待隊(duì)列中的任務(wù)執(zhí)行結(jié)束） - 任務(wù)按順序執(zhí)行达布，雖然并行隊(duì)列可以開啟多個(gè)線程团甲，并且同時(shí)執(zhí)行多個(gè)任務(wù)，但是因?yàn)橥綀?zhí)行不具備開啟線程的能力黍聂，只有當(dāng)前這一個(gè)線程躺苦，而且同步執(zhí)行需要等待隊(duì)列中的任務(wù)執(zhí)行結(jié)束身腻，再執(zhí)行下一個(gè)任務(wù)，所以任務(wù)只能一個(gè)接一個(gè)按照順序執(zhí)行匹厘。
2018-12-27 10:54:22.992819+0800 Thread[1210:37289] syncConcurrent start
2018-12-27 10:54:22.993023+0800 Thread[1210:37289] 任務(wù)一嘀趟，i = 0
2018-12-27 10:54:23.994423+0800 Thread[1210:37289] 任務(wù)一，i = 1
2018-12-27 10:54:24.995012+0800 Thread[1210:37289] 任務(wù)一愈诚，i = 2
2018-12-27 10:54:25.996057+0800 Thread[1210:37289] 任務(wù)二她按，i = 0
2018-12-27 10:54:26.997429+0800 Thread[1210:37289] 任務(wù)二，i = 1
2018-12-27 10:54:27.998885+0800 Thread[1210:37289] 任務(wù)二炕柔，i = 2
2018-12-27 10:54:29.000327+0800 Thread[1210:37289] syncConcurrent end
3.2.4.異步執(zhí)行 + 并發(fā)隊(duì)列
/*
異步執(zhí)行 + 并行隊(duì)列
開啟多個(gè)線程酌泰，任務(wù)交替執(zhí)行
*/
- (void)asyncConcurrent{
NSLog(@" asyncConcurrent start");
dispatch_queue_t queue = dispatch_queue_create("com.xiuxiu.asyncConcurrent", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二匕累，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
NSLog(@" asyncConcurrent end");
}
輸出結(jié)果：
- 開啟了2個(gè)新線程（異步執(zhí)行具備開啟線程的能力）
- 所有任務(wù)都在
asyncConcurrent start和asyncConcurrent end之后執(zhí)行（異步執(zhí)行不會(huì)等待陵刹，繼續(xù)執(zhí)行任務(wù)） - 任務(wù)交替執(zhí)行（異步執(zhí)行具備開啟線程的能力，并且并行隊(duì)列可以開啟多個(gè)線程欢嘿，同時(shí)執(zhí)行多個(gè)任務(wù)）
2018-12-27 11:18:23.174090+0800 Thread[1210:37289] asyncConcurrent start
2018-12-27 11:18:23.174253+0800 Thread[1210:37289] asyncConcurrent end
2018-12-27 11:18:23.174351+0800 Thread[1210:47038] 任務(wù)二衰琐，i = 0
2018-12-27 11:18:23.174401+0800 Thread[1210:37362] 任務(wù)一，i = 0
2018-12-27 11:18:24.177759+0800 Thread[1210:37362] 任務(wù)一际插，i = 1
2018-12-27 11:18:24.177759+0800 Thread[1210:47038] 任務(wù)二碘耳，i = 1
2018-12-27 11:18:25.178650+0800 Thread[1210:47038] 任務(wù)二，i = 2
2018-12-27 11:18:25.178650+0800 Thread[1210:37362] 任務(wù)一框弛，i = 2
3.2.5.同步執(zhí)行 + 主隊(duì)列
同步執(zhí)行 + 主隊(duì)列 在不同線程中調(diào)用辛辨，結(jié)果不一樣。
在主線程中調(diào)用瑟枫，出現(xiàn)死鎖
在其他線程中調(diào)用斗搞，不會(huì)開啟線程，一個(gè)任務(wù)執(zhí)行完畢后慷妙，再執(zhí)行下一個(gè)任務(wù)
3.2.5.1在主線程調(diào)用
/*
同步執(zhí)行 + 主隊(duì)列
在主線程中調(diào)用僻焚，出現(xiàn)死鎖
*/
- (void)syncMain{
NSLog(@" syncMain start");
dispatch_queue_t queue = dispatch_get_main_queue();
dispatch_sync(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_sync(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二膝擂，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
NSLog(@" syncMain end");
}
輸出結(jié)果：
在Xcode10 上運(yùn)行崩潰虑啤，只輸出了syncMain start
為什么？
因?yàn)槲覀冊(cè)谥骶€程中執(zhí)行 syncMain方法架馋，相當(dāng)于把 syncMain任務(wù)放到主線程的隊(duì)列中狞山，而同步執(zhí)行會(huì)等待當(dāng)前隊(duì)列中的任務(wù)執(zhí)行完畢后，才會(huì)接著執(zhí)行叉寂。我們把任務(wù)一追加到主隊(duì)列中萍启，任務(wù)一會(huì)等待主線程處理完syncMain方法，而syncMain方法又需要等待任務(wù)一執(zhí)行完畢，才能繼續(xù)執(zhí)行勘纯，雙方都在等待局服，所以線程死鎖，任務(wù)無(wú)法執(zhí)行驳遵。
2018-12-27 11:26:17.011738+0800 Thread[1443:50531] syncMain start
3.2.5.2 在其他線程調(diào)用
/*
同步執(zhí)行 + 主隊(duì)列
在其他線程中調(diào)用淫奔，不會(huì)開啟線程，一個(gè)任務(wù)執(zhí)行完畢后堤结，再執(zhí)行下一個(gè)任務(wù)
*/
- (void)syncMain{
NSLog(@"主線程");
dispatch_async(dispatch_get_global_queue(0, 0), ^{
NSLog(@" syncMain start");
dispatch_queue_t queue = dispatch_get_main_queue();
dispatch_sync(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一搏讶，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_sync(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
NSLog(@" syncMain end");
});
}
輸出結(jié)果：
- 沒(méi)有開啟線程霍殴，放在主隊(duì)列的任務(wù)都在主線程中執(zhí)行
- 所有任務(wù)都在
syncMain start和syncMain end之間執(zhí)行（同步執(zhí)行需要等待隊(duì)列中的任務(wù)執(zhí)行結(jié)束） - 任務(wù)按順序執(zhí)行（串行隊(duì)列每次只有一個(gè)任務(wù)被執(zhí)行，任務(wù)一個(gè)接著一個(gè)執(zhí)行）
2018-12-27 14:22:03.964047+0800 Thread[2134:84333] 主線程
2018-12-27 14:22:03.964238+0800 Thread[2134:84385] syncMain start
2018-12-27 14:22:03.965009+0800 Thread[2134:84333] 任務(wù)一系吩，i = 0
2018-12-27 14:22:04.966453+0800 Thread[2134:84333] 任務(wù)一来庭，i = 1
2018-12-27 14:22:05.967903+0800 Thread[2134:84333] 任務(wù)一，i = 2
2018-12-27 14:22:06.968817+0800 Thread[2134:84333] 任務(wù)二穿挨，i = 0
2018-12-27 14:22:07.969877+0800 Thread[2134:84333] 任務(wù)二月弛，i = 1
2018-12-27 14:22:08.970376+0800 Thread[2134:84333] 任務(wù)二，i = 2
2018-12-27 14:22:09.971810+0800 Thread[2134:84385] syncMain end
3.2.6.異步執(zhí)行 + 主隊(duì)列
/*
異步執(zhí)行 + 主隊(duì)列
不會(huì)開啟新線程科盛，在主線程中執(zhí)行帽衙，一個(gè)任務(wù)執(zhí)行完畢后，再執(zhí)行下一個(gè)任務(wù)
*/
- (void)asyncMain{
NSLog(@" asyncMain start");
dispatch_queue_t queue = dispatch_get_main_queue();
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一贞绵，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二厉萝，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
NSLog(@" asyncMain end");
}
輸出結(jié)果：
- 沒(méi)有開啟線程，放在主隊(duì)列的任務(wù)都在主線程中執(zhí)行
- 所有任務(wù)都在
asyncMain start和asyncMain end之后執(zhí)行(異步執(zhí)行不會(huì)等待榨崩，繼續(xù)執(zhí)行任務(wù)） - 任務(wù)按順序執(zhí)行（因?yàn)橹麝?duì)列是串行隊(duì)列谴垫，每次只有一個(gè)任務(wù)被執(zhí)行，任務(wù)一個(gè)接著一個(gè)執(zhí)行）
2018-12-27 14:33:15.293261+0800 Thread[2134:84333] asyncMain start
2018-12-27 14:33:15.293406+0800 Thread[2134:84333] asyncMain end
2018-12-27 14:33:15.293646+0800 Thread[2134:84333] 任務(wù)一母蛛，i = 0
2018-12-27 14:33:16.293875+0800 Thread[2134:84333] 任務(wù)一翩剪，i = 1
2018-12-27 14:33:17.295251+0800 Thread[2134:84333] 任務(wù)一，i = 2
2018-12-27 14:33:18.296751+0800 Thread[2134:84333] 任務(wù)二彩郊，i = 0
2018-12-27 14:33:19.297602+0800 Thread[2134:84333] 任務(wù)二前弯，i = 1
2018-12-27 14:33:20.298579+0800 Thread[2134:84333] 任務(wù)二，i = 2
4.線程間通信
在iOS開發(fā)工程中秫逝，我們一般在主線程中進(jìn)行UI刷新恕出，如：點(diǎn)擊、拖拽筷登、滾動(dòng)事件剃根，耗時(shí)操作放在其他線程中，而當(dāng)耗時(shí)操作結(jié)束后前方，回到主線程狈醉，就需要用到線程間的通信廉油。
在全局隊(duì)列中執(zhí)行任務(wù)，任務(wù)完成后苗傅，切回主線程
- (void)gcdCommunication{
NSLog(@"我在主線程");
dispatch_async(dispatch_get_global_queue(0, 0), ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一抒线，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"回到主線程");
});
});
}
輸出結(jié)果：
2018-12-27 15:05:55.188427+0800 Thread[2519:102865] 我在主線程
2018-12-27 15:05:55.188635+0800 Thread[2519:102899] 任務(wù)一，i = 0
2018-12-27 15:05:56.189689+0800 Thread[2519:102899] 任務(wù)一渣慕，i = 1
2018-12-27 15:05:57.191253+0800 Thread[2519:102899] 任務(wù)一嘶炭，i = 2
2018-12-27 15:05:58.195350+0800 Thread[2519:102865] 回到主線程
5.dispatch_once
創(chuàng)建單例或者整個(gè)程序只運(yùn)行一次的代碼，可以使用dispatch_once逊桦，dispatch_once函數(shù)保證這個(gè)程序運(yùn)行過(guò)程中只被執(zhí)行一次眨猎，即時(shí)在多線程情況下也是安全的。
/*
驗(yàn)證dispatch_once
*/
- (void)testGcdOnce{
dispatch_async(dispatch_get_global_queue(0, 0), ^{
for (NSInteger i = 0; i < 3; i ++) {
[self gcdOnce];
}
});
dispatch_async(dispatch_get_global_queue(0, 0), ^{
for (NSInteger i = 0; i < 3; i ++) {
[self gcdOnce];
}
});
}
- (void)gcdOnce{
NSLog(@"%s",__func__);
static TicketManager *manager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
manager = [[TicketManager alloc]init];
NSLog(@"創(chuàng)建對(duì)象");
});
}
輸出結(jié)果：dispatch_once里面只被執(zhí)行了一次
2018-12-27 15:19:31.228794+0800 Thread[2702:110251] -[ViewController gcdOnce]
2018-12-27 15:19:31.228794+0800 Thread[2702:110250] -[ViewController gcdOnce]
2018-12-27 15:19:31.229290+0800 Thread[2702:110251] 創(chuàng)建對(duì)象
2018-12-27 15:19:31.229516+0800 Thread[2702:110250] -[ViewController gcdOnce]
2018-12-27 15:19:31.229514+0800 Thread[2702:110251] -[ViewController gcdOnce]
2018-12-27 15:19:31.229630+0800 Thread[2702:110250] -[ViewController gcdOnce]
2018-12-27 15:19:31.229678+0800 Thread[2702:110251] -[ViewController gcdOnce]
6.dispatch_after
dispatch_after并不是在指定時(shí)間之后才執(zhí)行處理强经，而是在指定時(shí)間之后將任務(wù)追加到隊(duì)列中睡陪，這個(gè)指定時(shí)間并不是絕對(duì)準(zhǔn)確的，想要大致完成延時(shí)任務(wù)可以使用dispatch_after函數(shù)實(shí)現(xiàn)
- (void)gcdAfter{
NSLog(@"%s",__func__);
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
NSLog(@"%s",__func__);
});;
}
輸出結(jié)果：大致為1秒
2018-12-27 15:28:23.416958+0800 Thread[2781:114534] -[ViewController gcdAfter]
2018-12-27 15:28:24.513064+0800 Thread[2781:114534] -[ViewController gcdAfter]_block_invoke
7. dispatch_apply(快速迭代)
dispatch_apply快速迭代方法匿情，按照指定次數(shù)將指定的任務(wù)添加到隊(duì)列中兰迫，并等待隊(duì)列中的任務(wù)全部執(zhí)行結(jié)束。
如果在串行隊(duì)列中使用dispatch_apply函數(shù)炬称，就和for循環(huán)遍歷一樣汁果，按照順序執(zhí)行，體現(xiàn)不出快速迭代的意義玲躯。
如果在并行隊(duì)列中使用dispatch_apply函數(shù)据德，dispatch_apply可以在多個(gè)線程中同時(shí)遍歷多個(gè)數(shù)字。
7.1 在串行隊(duì)列使用dispatch_apply
將在主隊(duì)列dispatch_get_main_queue的遍歷任務(wù)放在并行隊(duì)列dispatch_get_global_queue中跷车，為了避免上面講的死鎖問(wèn)題,關(guān)注apply begin和apply end之間的代碼即可
/*
dispatch_apply:快速迭代
*/
- (void)gcdApply{
NSLog(@"主線程");
dispatch_async(dispatch_get_global_queue(0, 0), ^{
NSLog(@"apply begin");
dispatch_apply(6, dispatch_get_main_queue(), ^(size_t index) {
NSLog(@"index = %zu",index);
});
NSLog(@"apply end");
});
}
輸出結(jié)果：
- 沒(méi)有開啟線程（主隊(duì)列的任務(wù)只在主線程中執(zhí)行）
-
apply end在最后輸出（dispatch_apply函數(shù)會(huì)等待隊(duì)列全部任務(wù)執(zhí)行結(jié)束）
2018-12-27 15:58:28.788666+0800 Thread[3090:128936] 主線程
2018-12-27 15:58:28.788880+0800 Thread[3090:128988] apply begin
2018-12-27 15:58:28.819630+0800 Thread[3090:128936] index = 0
2018-12-27 15:58:28.819791+0800 Thread[3090:128936] index = 1
2018-12-27 15:58:28.819897+0800 Thread[3090:128936] index = 2
2018-12-27 15:58:28.820107+0800 Thread[3090:128936] index = 3
2018-12-27 15:58:28.820396+0800 Thread[3090:128936] index = 4
2018-12-27 15:58:28.820503+0800 Thread[3090:128936] index = 5
2018-12-27 15:58:28.820752+0800 Thread[3090:128988] apply end
7.2在并行隊(duì)列使用dispatch_apply
/*
dispatch_apply:快速迭代
*/
- (void)gcdApply{
NSLog(@"apply begin");
dispatch_apply(6, dispatch_get_global_queue(0, 0), ^(size_t index) {
NSLog(@"index = %zu",index);
});
NSLog(@"apply end");
}
輸出結(jié)果：
- 開啟線程（看線程編號(hào)得出）
-
apply end在最后輸出（dispatch_apply函數(shù)會(huì)等待隊(duì)列全部任務(wù)執(zhí)行結(jié)束）
2018-12-27 15:39:06.219402+0800 Thread[2918:120358] apply begin
2018-12-27 15:39:06.219636+0800 Thread[2918:120391] index = 1
2018-12-27 15:39:06.219619+0800 Thread[2918:120358] index = 0
2018-12-27 15:39:06.219746+0800 Thread[2918:120391] index = 3
2018-12-27 15:39:06.219747+0800 Thread[2918:120392] index = 4
2018-12-27 15:39:06.219737+0800 Thread[2918:120358] index = 2
2018-12-27 15:39:06.219832+0800 Thread[2918:120391] index = 5
2018-12-27 15:39:06.219933+0800 Thread[2918:120358] apply end
需求1：我們需要異步執(zhí)行兩個(gè)操作（一個(gè)操作可以是一個(gè)任務(wù)晋控，也可以是多個(gè)任務(wù)，這里是兩個(gè)任務(wù)）姓赤，而且第一組操作結(jié)束后赡译，才能開始第二組操作，如何實(shí)現(xiàn)呢不铆？
這里的意思其實(shí)保持線程同步蝌焚，將異步任務(wù)轉(zhuǎn)化為同步任務(wù)的意思。
方法1：使用柵欄函數(shù)
方法2：使用dispatch_group
方式3 ：使用dispatch_semaphore
這三個(gè)方法都會(huì)在下面一一講解的誓斥。
總結(jié)：就當(dāng)前這個(gè)需求只洒，使用柵欄函數(shù)會(huì)比較簡(jiǎn)單，所有方法講完具體實(shí)現(xiàn)就可以看出來(lái)了不用創(chuàng)建group或者semaphore,直接放個(gè)柵欄在中間劳坑，分隔兩個(gè)操作毕谴。
8.dispatch_barrier(柵欄函數(shù))
柵欄函數(shù)存在的意義：先執(zhí)行柵欄函數(shù)之前的任務(wù)，再執(zhí)行柵欄函數(shù)中的任務(wù)，最后執(zhí)行柵欄函數(shù)之后的任務(wù)涝开，增加?xùn)艡诤瘮?shù)不影響原有隊(duì)列的任務(wù)執(zhí)行方式循帐，也就是柵欄函數(shù)之前隊(duì)列的任務(wù)是什么執(zhí)行方式，柵欄函數(shù)之后隊(duì)列的任務(wù)還是什么執(zhí)行方式舀武。
柵欄函數(shù)分為：dispatch_barrier_async 和dispatch_barrier_sync
區(qū)別就是 :添加?xùn)艡诤瘮?shù)后面任務(wù)到隊(duì)列的時(shí)間不一樣拄养。
dispatch_barrier_sync：需要等待柵欄函數(shù)中的任務(wù)執(zhí)行結(jié)束后，才會(huì)添加?xùn)艡诤瘮?shù)后的任務(wù)到隊(duì)列中银舱。
dispatch_barrier_async ： 不需要等待柵欄函數(shù)中的任務(wù)執(zhí)行結(jié)束瘪匿，就已經(jīng)將柵欄函數(shù)后的任務(wù)到隊(duì)列中。
8.1 dispatch_barrier_sync
實(shí)現(xiàn)代碼
- (void)gcdBarrier{
NSLog(@"主線程");
dispatch_queue_t queue = dispatch_queue_create("com.xiuxiu.gcd", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一寻馏，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二棋弥，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
//1.dispatch_barrier_sync
dispatch_barrier_sync(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" barrier1，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" barrier2诚欠，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
NSLog(@"---------barrier代碼后面----------------");
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)三嘁锯，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)四，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
}
輸出結(jié)果：
-
先執(zhí)行任務(wù)一聂薪、二，再執(zhí)行柵欄函數(shù)中的barrier1蝗羊、barrier2藏澳，最后執(zhí)行任務(wù)三、四耀找； - 任務(wù)一翔悠、二交替執(zhí)行（異步執(zhí)行），任務(wù)三野芒、四交替執(zhí)行(異步執(zhí)行)蓄愁，印證柵欄函數(shù)不影響隊(duì)列任務(wù)的執(zhí)行方式；
- 橫線在柵欄函數(shù)之后輸出（
dispatch_barrier_sync：需要等待柵欄函數(shù)中的任務(wù)執(zhí)行結(jié)束后狞悲，才會(huì)添加?xùn)艡诤瘮?shù)后的任務(wù)到隊(duì)列中）撮抓。
2018-12-28 17:07:54.227141+0800 Thread[11766:169507] 主線程
2018-12-28 17:07:54.227455+0800 Thread[11766:169563] 任務(wù)二，i = 0
2018-12-28 17:07:54.227482+0800 Thread[11766:169565] 任務(wù)一摇锋，i = 0
2018-12-28 17:07:55.231426+0800 Thread[11766:169563] 任務(wù)二丹拯，i = 1
2018-12-28 17:07:55.231426+0800 Thread[11766:169565] 任務(wù)一，i = 1
2018-12-28 17:07:56.232952+0800 Thread[11766:169563] 任務(wù)二荸恕，i = 2
2018-12-28 17:07:56.232985+0800 Thread[11766:169565] 任務(wù)一乖酬，i = 2
2018-12-28 17:07:57.236980+0800 Thread[11766:169507] barrier1，i = 0
2018-12-28 17:07:58.238423+0800 Thread[11766:169507] barrier1融求，i = 1
2018-12-28 17:07:59.239776+0800 Thread[11766:169507] barrier1咬像，i = 2
2018-12-28 17:08:00.240315+0800 Thread[11766:169507] barrier2，i = 0
2018-12-28 17:08:01.240863+0800 Thread[11766:169507] barrier2，i = 1
2018-12-28 17:08:02.242310+0800 Thread[11766:169507] barrier2县昂，i = 2
2018-12-28 17:08:03.242826+0800 Thread[11766:169507] ---------barrier代碼后面----------------
2018-12-28 17:08:03.243200+0800 Thread[11766:169564] 任務(wù)三肮柜，i = 0
2018-12-28 17:08:03.243315+0800 Thread[11766:169663] 任務(wù)四，i = 0
2018-12-28 17:08:04.247765+0800 Thread[11766:169663] 任務(wù)四七芭，i = 1
2018-12-28 17:08:04.247765+0800 Thread[11766:169564] 任務(wù)三素挽，i = 1
2018-12-28 17:08:05.252405+0800 Thread[11766:169663] 任務(wù)四，i = 2
2018-12-28 17:08:05.252405+0800 Thread[11766:169564] 任務(wù)三狸驳，i = 2
8.2dispatch_barrier_async
實(shí)現(xiàn)代碼
- (void)gcdBarrier{
NSLog(@"主線程");
dispatch_queue_t queue = dispatch_queue_create("com.xiuxiu.gcd", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一预明，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
//2.dispatch_barrier_async
dispatch_barrier_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" barrier1耙箍，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" barrier2撰糠，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
NSLog(@"---------barrier代碼后面----------------");
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)三，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)四辩昆，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
}
輸出結(jié)果：
-
先執(zhí)行任務(wù)一阅酪、二，再執(zhí)行柵欄函數(shù)中的barrier1汁针、barrier2术辐，最后執(zhí)行任務(wù)三、四施无； - 任務(wù)一辉词、二交替執(zhí)行（異步執(zhí)行），任務(wù)三猾骡、四交替執(zhí)行(異步執(zhí)行)瑞躺，印證柵欄函數(shù)不影響隊(duì)列任務(wù)的執(zhí)行方式；
- 橫線在柵欄函數(shù)之前輸出（
dispatch_barrier_async：不需要等待柵欄函數(shù)中的任務(wù)執(zhí)行結(jié)束兴想，就已經(jīng)將柵欄函數(shù)后的任務(wù)到隊(duì)列中）幢哨。
2018-12-28 17:10:58.908322+0800 Thread[11798:171154] 主線程
2018-12-28 17:10:58.908586+0800 Thread[11798:171209] 任務(wù)一，i = 0
2018-12-28 17:10:58.908586+0800 Thread[11798:171154] ---------barrier代碼后面----------------
2018-12-28 17:10:58.908616+0800 Thread[11798:171207] 任務(wù)二嫂便，i = 0
2018-12-28 17:10:59.912811+0800 Thread[11798:171207] 任務(wù)二捞镰，i = 1
2018-12-28 17:10:59.912811+0800 Thread[11798:171209] 任務(wù)一，i = 1
2018-12-28 17:11:00.917006+0800 Thread[11798:171207] 任務(wù)二毙替，i = 2
2018-12-28 17:11:00.917047+0800 Thread[11798:171209] 任務(wù)一曼振，i = 2
2018-12-28 17:11:01.919238+0800 Thread[11798:171209] barrier1，i = 0
2018-12-28 17:11:02.921574+0800 Thread[11798:171209] barrier1蔚龙，i = 1
2018-12-28 17:11:03.924472+0800 Thread[11798:171209] barrier1冰评，i = 2
2018-12-28 17:11:04.929280+0800 Thread[11798:171209] barrier2，i = 0
2018-12-28 17:11:05.930060+0800 Thread[11798:171209] barrier2木羹，i = 1
2018-12-28 17:11:06.931831+0800 Thread[11798:171209] barrier2甲雅，i = 2
2018-12-28 17:11:07.934022+0800 Thread[11798:171209] 任務(wù)三解孙，i = 0
2018-12-28 17:11:07.934022+0800 Thread[11798:171207] 任務(wù)四，i = 0
2018-12-28 17:11:08.939572+0800 Thread[11798:171207] 任務(wù)四抛人，i = 1
2018-12-28 17:11:08.939573+0800 Thread[11798:171209] 任務(wù)三弛姜，i = 1
2018-12-28 17:11:09.942792+0800 Thread[11798:171209] 任務(wù)三，i = 2
2018-12-28 17:11:09.942829+0800 Thread[11798:171207] 任務(wù)四妖枚，i = 2
9.dispatch_group(隊(duì)列組)
任務(wù)的執(zhí)行是先創(chuàng)建一個(gè)任務(wù)廷臼，放入隊(duì)列進(jìn)行執(zhí)行。而隊(duì)列組就是用來(lái)存放隊(duì)列的一個(gè)組绝页。
將隊(duì)列放入隊(duì)列組中可以使用 dispatch_group_async 或者dispatch_group_enter 和dispatch_group_leave的組合實(shí)現(xiàn)荠商。
隊(duì)列組的任務(wù)結(jié)束完成后，調(diào)用dispatch_group_notify 可以回到指定線程執(zhí)行任務(wù)续誉，調(diào)用dispatch_group_wait可以回到當(dāng)前線程執(zhí)行任務(wù)（阻塞當(dāng)前線程）莱没。
就上面的需求1，用dispatch_group方式實(shí)現(xiàn)
1. 我們用dispatch_group_async + dispatch_group_notify來(lái)進(jìn)行實(shí)現(xiàn)
- (void)requirementGroupAsync{
NSLog(@"主線程");
dispatch_queue_t queue = dispatch_queue_create("com.gcd.group", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一酷鸦，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_group_async(group, queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二饰躲，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_group_notify(group, queue, ^{
NSLog(@"------dispatch_group_notify------");
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)三，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)四臼隔，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
});
}
輸出結(jié)果：先執(zhí)行任務(wù)一嘹裂、二，再執(zhí)行任務(wù)三摔握、四寄狼；
2018-12-28 17:59:23.695495+0800 Thread[12227:189820] 主線程
2018-12-28 17:59:23.695775+0800 Thread[12227:189867] 任務(wù)一，i = 0
2018-12-28 17:59:23.695778+0800 Thread[12227:189868] 任務(wù)二盒发，i = 0
2018-12-28 17:59:24.697513+0800 Thread[12227:189867] 任務(wù)一，i = 1
2018-12-28 17:59:24.697514+0800 Thread[12227:189868] 任務(wù)二狡逢，i = 1
2018-12-28 17:59:25.701243+0800 Thread[12227:189868] 任務(wù)二宁舰，i = 2
2018-12-28 17:59:25.701243+0800 Thread[12227:189867] 任務(wù)一，i = 2
2018-12-28 17:59:26.705407+0800 Thread[12227:189868] ------dispatch_group_notify------
2018-12-28 17:59:26.705799+0800 Thread[12227:189868] 任務(wù)三奢浑，i = 0
2018-12-28 17:59:26.705803+0800 Thread[12227:189866] 任務(wù)四蛮艰，i = 0
2018-12-28 17:59:27.709876+0800 Thread[12227:189868] 任務(wù)三，i = 1
2018-12-28 17:59:27.709873+0800 Thread[12227:189866] 任務(wù)四雀彼，i = 1
2018-12-28 17:59:28.713711+0800 Thread[12227:189866] 任務(wù)四壤蚜，i = 2
2018-12-28 17:59:28.713711+0800 Thread[12227:189868] 任務(wù)三，i = 2
2. 我們用dispatch_group_async + dispatch_group_wait來(lái)進(jìn)行實(shí)現(xiàn)
- (void)requirementGroupAsync{
NSLog(@"主線程");
dispatch_queue_t queue = dispatch_queue_create("com.gcd.group", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一徊哑，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_group_async(group, queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二袜刷，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
//2.dispatch_group_wait
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
NSLog(@"-----dispatch_group_wait----");
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)三，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)四莺丑，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
}
輸出結(jié)果：
- 先執(zhí)行任務(wù)一著蟹、二墩蔓，再執(zhí)行任務(wù)三、四萧豆；
-
dispatch_group_wait在主線程輸出奸披，就如之前所說(shuō)dispatch_group_wait會(huì)阻塞當(dāng)前線程。
2018-12-28 18:07:54.379565+0800 Thread[12300:193286] 主線程
2018-12-28 18:07:54.379782+0800 Thread[12300:193334] 任務(wù)二涮雷，i = 0
2018-12-28 18:07:54.379783+0800 Thread[12300:193332] 任務(wù)一阵面，i = 0
2018-12-28 18:07:55.384688+0800 Thread[12300:193334] 任務(wù)二，i = 1
2018-12-28 18:07:55.384720+0800 Thread[12300:193332] 任務(wù)一洪鸭，i = 1
2018-12-28 18:07:56.385807+0800 Thread[12300:193332] 任務(wù)一样刷，i = 2
2018-12-28 18:07:56.385808+0800 Thread[12300:193334] 任務(wù)二，i = 2
2018-12-28 18:07:57.386847+0800 Thread[12300:193286] -----dispatch_group_wait----
2018-12-28 18:07:57.387161+0800 Thread[12300:193334] 任務(wù)三卿嘲，i = 0
2018-12-28 18:07:57.387174+0800 Thread[12300:193332] 任務(wù)四颂斜，i = 0
2018-12-28 18:07:58.387806+0800 Thread[12300:193332] 任務(wù)四，i = 1
2018-12-28 18:07:58.387808+0800 Thread[12300:193334] 任務(wù)三拾枣，i = 1
2018-12-28 18:07:59.390173+0800 Thread[12300:193332] 任務(wù)四沃疮，i = 2
2018-12-28 18:07:59.390209+0800 Thread[12300:193334] 任務(wù)三，i = 2
3. 我們用dispatch_group_enter + dispatch_group_leave + dispatch_group_notify來(lái)進(jìn)行實(shí)現(xiàn)
- (void)requirementGroupEnter{
NSLog(@"主線程");
dispatch_queue_t queue = dispatch_queue_create("com.gcd.group", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一梅肤，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
dispatch_group_leave(group);
});
dispatch_group_enter(group);
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二司蔬，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
dispatch_group_leave(group);
});
//1.dispatch_group_notify
dispatch_group_notify(group, queue, ^{
NSLog(@"------dispatch_group_notify------");
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)三左医，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)四，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
});
}
輸出結(jié)果：先執(zhí)行任務(wù)一芥映、二奈偏，再執(zhí)行任務(wù)三唁盏、四；
2018-12-28 18:19:52.294127+0800 Thread[12422:198467] 主線程
2018-12-28 18:19:52.294429+0800 Thread[12422:198501] 任務(wù)一刽严，i = 0
2018-12-28 18:19:52.294438+0800 Thread[12422:198504] 任務(wù)二撑螺，i = 0
2018-12-28 18:19:53.297632+0800 Thread[12422:198504] 任務(wù)二主胧，i = 1
2018-12-28 18:19:53.297642+0800 Thread[12422:198501] 任務(wù)一，i = 1
2018-12-28 18:19:54.302891+0800 Thread[12422:198501] 任務(wù)一诀黍，i = 2
2018-12-28 18:19:54.302891+0800 Thread[12422:198504] 任務(wù)二歇拆，i = 2
2018-12-28 18:19:55.307933+0800 Thread[12422:198501] ------dispatch_group_notify------
2018-12-28 18:19:55.308242+0800 Thread[12422:198501] 任務(wù)三渠啊，i = 0
2018-12-28 18:19:55.308258+0800 Thread[12422:198502] 任務(wù)四，i = 0
2018-12-28 18:19:56.312331+0800 Thread[12422:198501] 任務(wù)三权旷，i = 1
2018-12-28 18:19:56.312331+0800 Thread[12422:198502] 任務(wù)四替蛉，i = 1
2018-12-28 18:19:57.313584+0800 Thread[12422:198502] 任務(wù)四，i = 2
2018-12-28 18:19:57.313584+0800 Thread[12422:198501] 任務(wù)三拄氯，i = 2
4. 我們用dispatch_group_enter + dispatch_group_leave + dispatch_group_wait來(lái)進(jìn)行實(shí)現(xiàn)
- (void)requirementGroupEnter{
NSLog(@"主線程");
dispatch_queue_t queue = dispatch_queue_create("com.gcd.group", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一躲查，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
dispatch_group_leave(group);
});
dispatch_group_enter(group);
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)二，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
dispatch_group_leave(group);
});
// 2.dispatch_group_wait
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
NSLog(@"-----dispatch_group_wait----");
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)三译柏，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)四镣煮，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
}
- 先執(zhí)行任務(wù)一、二鄙麦，再執(zhí)行任務(wù)三典唇、四；
-
dispatch_group_wait在主線程輸出黔衡，就如之前所說(shuō)dispatch_group_wait會(huì)阻塞當(dāng)前線程
2018-12-28 18:21:29.197243+0800 Thread[12446:199547] 主線程
2018-12-28 18:21:29.197534+0800 Thread[12446:199590] 任務(wù)一蚓聘，i = 0
2018-12-28 18:21:29.197598+0800 Thread[12446:199591] 任務(wù)二，i = 0
2018-12-28 18:21:30.200867+0800 Thread[12446:199591] 任務(wù)二盟劫，i = 1
2018-12-28 18:21:30.200870+0800 Thread[12446:199590] 任務(wù)一夜牡，i = 1
2018-12-28 18:21:31.204217+0800 Thread[12446:199590] 任務(wù)一，i = 2
2018-12-28 18:21:31.204215+0800 Thread[12446:199591] 任務(wù)二侣签，i = 2
2018-12-28 18:21:32.205551+0800 Thread[12446:199547] -----dispatch_group_wait----
2018-12-28 18:21:32.205926+0800 Thread[12446:199590] 任務(wù)三塘装，i = 0
2018-12-28 18:21:32.205930+0800 Thread[12446:199591] 任務(wù)四，i = 0
2018-12-28 18:21:33.210243+0800 Thread[12446:199590] 任務(wù)三影所，i = 1
2018-12-28 18:21:33.210413+0800 Thread[12446:199591] 任務(wù)四蹦肴，i = 1
2018-12-28 18:21:34.215728+0800 Thread[12446:199590] 任務(wù)三，i = 2
2018-12-28 18:21:34.215728+0800 Thread[12446:199591] 任務(wù)四猴娩，i = 2
那dispatch_group_async和dispatch_group_enter + dispatch_group_leave有什么區(qū)別呢阴幌？
需求2：異步執(zhí)行兩個(gè)網(wǎng)絡(luò)請(qǐng)求，兩個(gè)網(wǎng)絡(luò)請(qǐng)求執(zhí)行結(jié)束后卷中，進(jìn)行一定的操作矛双。
這里sendRequest用來(lái)代表網(wǎng)絡(luò)請(qǐng)求
- (void)sendRequest:(void (^)(void))block{
dispatch_async(dispatch_get_global_queue(0, 0), ^{
NSLog(@"start task 1");
[NSThread sleepForTimeInterval:3];
NSLog(@"end task 1");
dispatch_async(dispatch_get_main_queue(), ^{
if (block) {
block();
}
});
});
}
- (void)sendRequest2:(void (^)(void))block{
dispatch_async(dispatch_get_global_queue(0, 0), ^{
NSLog(@"start task 2");
[NSThread sleepForTimeInterval:3];
NSLog(@"end task 2");
dispatch_async(dispatch_get_main_queue(), ^{
if (block) {
block();
}
});
});
}
1. 用dispatch_group_async實(shí)現(xiàn)
- (void)gcdGroupAsync{
NSLog(@"主線程");
// dispatch_group_async 里面，應(yīng)該放同步代碼蟆豫，而不是異步代碼
dispatch_queue_t queue = dispatch_queue_create("com.gcd.group", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, queue, ^{
[self sendRequest:^{
NSLog(@"sendRequest done");
}];
});
dispatch_group_async(group, queue, ^{
[self sendRequest2:^{
NSLog(@"sendRequest2 done");
}];
});
dispatch_group_notify(group, queue, ^{
NSLog(@"all task over");
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"回到主線程刷新UI");
});
});
}
輸出結(jié)果：顯示不符合需求议忽，task1和task2還沒(méi)有結(jié)束，就輸出all task over 咯十减，為啥子呢栈幸？
原因：因?yàn)?code>dispatch_group_async里面放入的是異步的任務(wù)愤估，dispatch_group_async執(zhí)行了sendRequest這行代碼后，就認(rèn)為sendRequest已經(jīng)執(zhí)行完畢了(其實(shí)還沒(méi)有回調(diào)回來(lái))速址，group不再持有這個(gè)任務(wù)玩焰，就會(huì)執(zhí)行下面的dispatch_group_async，而sendRequest2同理芍锚，group沒(méi)有任務(wù)時(shí)震捣，就會(huì)執(zhí)行dispatch_group_notify 里面的任務(wù)，所以造成這樣子的輸出結(jié)果闹炉。
由此可見(jiàn)：dispatch_group_async里面適合放入同步代碼蒿赢，而不是異步代碼。
2018-12-29 17:13:42.710421+0800 Thread[17395:417245] 主線程
2018-12-29 17:13:42.710700+0800 Thread[17395:417334] start task 2
2018-12-29 17:13:42.710726+0800 Thread[17395:417333] all task over
2018-12-29 17:13:42.710708+0800 Thread[17395:417331] start task 1
2018-12-29 17:13:42.733662+0800 Thread[17395:417245] 回到主線程刷新UI
2018-12-29 17:13:45.714431+0800 Thread[17395:417331] end task 1
2018-12-29 17:13:45.714511+0800 Thread[17395:417334] end task 2
2018-12-29 17:13:45.714752+0800 Thread[17395:417245] sendRequest done
2018-12-29 17:13:45.714854+0800 Thread[17395:417245] sendRequest2 done
2.用dispatch_group_enter + dispatch_group_leave 實(shí)現(xiàn)
- (void)gcdGroupEnter{
NSLog(@"主線程");
dispatch_queue_t queue = dispatch_queue_create("com.gcd.group", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
[self sendRequest:^{
NSLog(@"sendRequest done");
dispatch_group_leave(group);
}];
dispatch_group_enter(group);
[self sendRequest2:^{
NSLog(@"sendRequest2 done");
dispatch_group_leave(group);
}];
dispatch_group_notify(group, queue, ^{
NSLog(@"all task over");
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"回到主線程刷新UI");
});
});
}
輸出結(jié)果：當(dāng)task1 和task2執(zhí)行結(jié)束后渣触，才輸出all task over羡棵，符合我們的需求。
當(dāng)我們調(diào)用sendRequest時(shí)嗅钻，先調(diào)用dispatch_group_enter時(shí)皂冰，任務(wù)回調(diào)后再調(diào)用dispatch_group_leave，整個(gè)異步操作中养篓，任務(wù)是被group持有的秃流，只有回調(diào)結(jié)束后才離開group，所以不會(huì)出現(xiàn)上面的問(wèn)題柳弄。
注意:dispatch_group_enter和dispatch_group_leave成對(duì)存在
2018-12-29 17:32:12.739361+0800 Thread[17557:425760] 主線程
2018-12-29 17:32:12.739608+0800 Thread[17557:425809] start task 1
2018-12-29 17:32:12.739608+0800 Thread[17557:425810] start task 2
2018-12-29 17:32:15.742987+0800 Thread[17557:425809] end task 1
2018-12-29 17:32:15.742990+0800 Thread[17557:425810] end task 2
2018-12-29 17:32:15.743325+0800 Thread[17557:425760] sendRequest2 done
2018-12-29 17:32:15.743528+0800 Thread[17557:425760] sendRequest done
2018-12-29 17:32:15.743742+0800 Thread[17557:425810] all task over
2018-12-29 17:32:15.744000+0800 Thread[17557:425760] 回到主線程刷新UI
10.dispatch_semaphore(信號(hào)量)
dispatch_semaphore 使用計(jì)數(shù)來(lái)完成這個(gè)問(wèn)題舶胀，計(jì)數(shù)為0 ，不可以通過(guò)碧注，計(jì)數(shù)大于等于1嚣伐，可以通過(guò)
其中有三個(gè)函數(shù)分別為：
-
dispatch_semaphore_create：創(chuàng)建semaphore并初始化信號(hào)量,初始化的值大于等于0； -
dispatch_semaphore_signal：信號(hào)量+1萍丐； -
dispatch_semaphore_wait： 判斷當(dāng)前信號(hào)量的值轩端，如果當(dāng)前信號(hào)量大于0，信號(hào)量-1逝变，往下執(zhí)行基茵，如果當(dāng)前信號(hào)量等于0，就會(huì)阻塞在當(dāng)前線程壳影，一直等待拱层。
用處：
1、保持線程同步态贤，將異步任務(wù)轉(zhuǎn)化為同步任務(wù)
2舱呻、保證線程安全醋火，為線程加鎖
線程安全：在多個(gè)線程中同時(shí)訪問(wèn)并操作同一對(duì)象時(shí)悠汽，運(yùn)行結(jié)果與預(yù)期的值相同就是線程安全箱吕。
線程安全問(wèn)題都是由全局變量及靜態(tài)變量引起的，若每個(gè)線程中對(duì)全局變量柿冲、靜態(tài)變量只有讀操作茬高，而無(wú)寫操作，一般來(lái)說(shuō)假抄，這個(gè)全局變量是線程安全的怎栽；若有多個(gè)線程同時(shí)執(zhí)行寫操作，一般都需要考慮線程同步宿饱，否則的話就可能影響線程安全熏瞄。
線程同步：可理解為線程A和B一塊配合，A執(zhí)行到一定程度時(shí)要依靠B的某個(gè)結(jié)果谬以，于是停下來(lái)强饮，示意B運(yùn)行；B依言執(zhí)行为黎，再將結(jié)果給A邮丰；A再繼續(xù)操作。
10.1.保持線程同步铭乾，將異步任務(wù)轉(zhuǎn)化為同步任務(wù)
這個(gè)也可以用來(lái)實(shí)現(xiàn)上面的需求1
- (void)gcdSemaphore{
NSLog(@"主線程");
dispatch_queue_t queue = dispatch_queue_create("com.xiuxiu.gcd", DISPATCH_QUEUE_CONCURRENT);
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)一剪廉，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
long x = dispatch_semaphore_signal(semaphore);
NSLog(@"signal后的信號(hào)量 = %ld",x);
});
long x = dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"wait后的信號(hào)量 = %ld",x);
NSLog(@"---dispatch_semaphore_wait-----");
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)三，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
dispatch_async(queue, ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@" 任務(wù)四炕檩，i = %ld",(long)i);
[NSThread sleepForTimeInterval:1.0];
}
});
}
輸出結(jié)果：
- 先輸出任務(wù)一斗蒋，再輸出任務(wù)三、四
-
dispatch_semaphore_wait在主線程輸出（信號(hào)量為0 笛质，阻塞在當(dāng)前線程）
我們?cè)谥骶€程創(chuàng)建了一個(gè)信號(hào)量賦值為0吹泡，并開辟了一個(gè)并行隊(duì)列異步執(zhí)行任務(wù)一，因?yàn)槭且粋€(gè)異步操作经瓷，此時(shí)不會(huì)等待任務(wù)一執(zhí)行結(jié)束爆哑， 直接執(zhí)行到dispatch_semaphore_wait，此時(shí)判斷出信號(hào)量的值0舆吮，不可通行揭朝，阻塞當(dāng)前線程，當(dāng)運(yùn)行到dispatch_semaphore_signal時(shí)色冀，信號(hào)量加1后等于1大于0潭袱，可通行，執(zhí)行dispatch_semaphore_wait后面的任務(wù)三锋恬、四屯换，通行后信號(hào)量減1等于0。
2018-12-29 15:22:24.960944+0800 Thread[16315:368237] 主線程
2018-12-29 15:22:24.961180+0800 Thread[16315:368286] 任務(wù)一，i = 0
2018-12-29 15:22:25.965568+0800 Thread[16315:368286] 任務(wù)一彤悔，i = 1
2018-12-29 15:22:26.970160+0800 Thread[16315:368286] 任務(wù)一嘉抓，i = 2
2018-12-29 15:22:27.975627+0800 Thread[16315:368237] wait后的信號(hào)量 = 0
2018-12-29 15:22:27.975627+0800 Thread[16315:368286] signal后的信號(hào)量 = 1
2018-12-29 15:22:27.975956+0800 Thread[16315:368237] ---dispatch_semaphore_wait-----
2018-12-29 15:22:27.976232+0800 Thread[16315:368287] 任務(wù)四，i = 0
2018-12-29 15:22:27.976285+0800 Thread[16315:368286] 任務(wù)三晕窑，i = 0
2018-12-29 15:22:28.978431+0800 Thread[16315:368286] 任務(wù)三抑片，i = 1
2018-12-29 15:22:28.978445+0800 Thread[16315:368287] 任務(wù)四，i = 1
2018-12-29 15:22:29.980405+0800 Thread[16315:368286] 任務(wù)三杨赤，i = 2
2018-12-29 15:22:29.980405+0800 Thread[16315:368287] 任務(wù)四敞斋，i = 2
10.2.保證線程安全，為線程加鎖
在上面講NSThread的時(shí)候疾牲，講過(guò)synchronized和NSCondition加鎖方式植捎，這里使用dispatch_semaphore進(jìn)行加密,運(yùn)行結(jié)果和上面一致。
- (void)sale{
while (1) {
//1阳柔、synchronized
// @synchronized (self) {
// if (self.tickets > 0 ) {
// [NSThread sleepForTimeInterval:0.1];
// self.tickets --;
// self.saleCount = Total - self.tickets;
// NSLog(@"%@ , 賣出 = %d鸥跟，剩余= %d",[NSThread currentThread].name,self.saleCount,self.tickets);
// }else{
// break;//一定要break，不然就會(huì)死循環(huán)
// }
// }
// 2盔沫、NSCondition
// [self.condition lock];
// if (self.tickets > 0 ) {
// [NSThread sleepForTimeInterval:0.1];
// self.tickets --;
// self.saleCount = Total - self.tickets;
// NSLog(@"%@ , 賣出 = %d医咨，剩余= %d",[NSThread currentThread].name,self.saleCount,self.tickets);
// }else{
// break;
// }
// [self.condition unlock];
//
//3、dispatch_semaphore方式
dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
if (self.tickets > 0 ) {
[NSThread sleepForTimeInterval:0.1];
self.tickets --;
self.saleCount = Total - self.tickets;
NSLog(@"%@ , 賣出 = %d架诞，剩余= %d",[NSThread currentThread].name,self.saleCount,self.tickets);
}else{
dispatch_semaphore_signal(self.semaphore);
break;
}
dispatch_semaphore_signal(self.semaphore);
}
}
信號(hào)量還需要多看點(diǎn)資料拟淮，這里就先這樣子吧~~
上面就保持線程同步，將異步任務(wù)轉(zhuǎn)化為同步任務(wù)谴忧，保證線程安全很泊，給線程加鎖就講了好多種方式，選擇的時(shí)候沾谓，針對(duì)需求而言來(lái)選擇一個(gè)較好的方式就OK啦~
參考博客：
iOS多線程慕課網(wǎng)視頻
深入理解iOS開發(fā)中的鎖
文章鏈接：
iOS 多線程- pThread和NSThread
iOS 多線程-NSOperation + NSOperationQueue
喜歡就點(diǎn)個(gè)贊吧????
有錯(cuò)之處委造，還請(qǐng)指出，感謝????
