GCD多線程應(yīng)用

概念

在GCD中有兩個重要的概念：任務(wù)和隊列狞尔。

任務(wù)

所要執(zhí)行的操作潘靖。任務(wù)有兩種執(zhí)行方式：同步執(zhí)行和異步執(zhí)行降淮。

同步執(zhí)行：
1. 會阻塞當(dāng)前線程逐沙，直到任務(wù)執(zhí)行完成才會返回當(dāng)前線程繼續(xù)運行
2. 不具備開啟新線程的能力
異步執(zhí)行：
1. 不會阻塞當(dāng)前線程洛史，會立即返回當(dāng)前線程繼續(xù)運行
2. 具備開啟新線程的能力

隊列

用于存放任務(wù)。隊列有兩種：串行隊列和并發(fā)隊列酱吝。

串行隊列：

任務(wù)執(zhí)行遵循先進(jìn)先出的順序也殖，下一個任務(wù)在上一個任務(wù)執(zhí)行完成后開始執(zhí)行
創(chuàng)建方式（兩種）

dispatch_queue_t serialQueue = dispatch_queue_create("com.apress.mySerialQueue", nil) ;
dispatch_queue_t serialQueue = dispatch_queue_create("com.apress.mySerialQueue", DISPATCH_QUEUE_SERIAL) ;

并發(fā)隊列：

任務(wù)執(zhí)行遵循先進(jìn)先出的順序，下一個任務(wù)可以在上一個任務(wù)執(zhí)行完成前開始執(zhí)行
創(chuàng)建方式

dispatch_queue_t concurrentQueue = dispatch_queue_create("com.appress.myConcurrentQueue",DISPATCH_QUEUE_CONCURRENT) ;

系統(tǒng)提供了四種全局的并發(fā)隊列务热，這些隊列通過優(yōu)先級加以區(qū)別忆嗜。高優(yōu)先級隊列中的任務(wù)會比在默認(rèn)或低優(yōu)先級隊列中的任務(wù)先執(zhí)行，而默認(rèn)級別隊列的優(yōu)先級又高于低優(yōu)先級隊列崎岂。被設(shè)置成后臺級別的隊列捆毫，它會等待所有比它級別高的隊列中的任務(wù)執(zhí)行完或CPU空閑的時候才會執(zhí)行自己的任務(wù)

dispatch_queue_t  concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) ;

字段	優(yōu)先級
DISPATCH_QUEUE_PRIORITY_HIGH	高優(yōu)先級
DISPATCH_QUEUE_PRIORITY_DEFAULT	默認(rèn)優(yōu)先級
DISPATCH_QUEUE_PRIORITY_LOW	低優(yōu)先級
DISPATCH_QUEUE_PRIORITY_BACKGROUND	后臺級別

主隊列：
除了串行隊列和并發(fā)隊列，還有一種特殊的隊列——主隊列冲甘。
1. 是串行隊列
2. 所有放在主隊列中的任務(wù)都會放到主線程中執(zhí)行
3. 可通過dispatch_get_main_queue()獲得

GCD的多線程使用

使用步驟

創(chuàng)建隊列
向隊列中添加任務(wù)：
- 通過dispatch_async進(jìn)行異步添加
- 通過dispatch_sync進(jìn)行同步添加

使用方式

由于存在不同的隊列和任務(wù)執(zhí)行方式绩卤，因此有多種組合方式來使用。

并發(fā)隊列+同步執(zhí)行

- (void)test {
    NSLog(@"=============begin") ;
    dispatch_queue_t myQueue = dispatch_queue_create("com.appress.myQueue",DISPATCH_QUEUE_CONCURRENT) ;
    dispatch_sync(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"1=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_sync(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"2=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_sync(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"3=========%@",[NSThread currentThread]) ;
        }
    }) ;
    NSLog(@"=============end") ;
}

打印結(jié)果為：

2017-05-03 14:59:35.976 test[1022:28719] =============begin
2017-05-03 14:59:35.977 test[1022:28719] 1=========<NSThread: 0x600000071240>{number = 1, name = main}
2017-05-03 14:59:35.977 test[1022:28719] 1=========<NSThread: 0x600000071240>{number = 1, name = main}
2017-05-03 14:59:35.977 test[1022:28719] 2=========<NSThread: 0x600000071240>{number = 1, name = main}
2017-05-03 14:59:35.977 test[1022:28719] 2=========<NSThread: 0x600000071240>{number = 1, name = main}
2017-05-03 14:59:35.977 test[1022:28719] 3=========<NSThread: 0x600000071240>{number = 1, name = main}
2017-05-03 14:59:35.977 test[1022:28719] 3=========<NSThread: 0x600000071240>{number = 1, name = main}
2017-05-03 14:59:35.978 test[1022:28719] =============end

不會開啟新線程江醇，而是在當(dāng)前線程執(zhí)行
任務(wù)按照順序一個一個執(zhí)行
會阻塞當(dāng)前線程

并發(fā)隊列+異步執(zhí)行

- (void)test {
    NSLog(@"=============begin") ;
    dispatch_queue_t myQueue = dispatch_queue_create("com.appress.myQueue",DISPATCH_QUEUE_CONCURRENT) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"1=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"2=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"3=========%@",[NSThread currentThread]) ;
        }
    }) ;
    NSLog(@"=============end") ;
}

打印結(jié)果為：

2017-05-03 15:04:37.047 test[1064:39634] =============begin
2017-05-03 15:04:37.047 test[1064:39634] =============end
2017-05-03 15:04:37.048 test[1064:39685] 2=========<NSThread: 0x60800007bc00>{number = 4, name = (null)}
2017-05-03 15:04:37.048 test[1064:39690] 1=========<NSThread: 0x60800007bd00>{number = 3, name = (null)}
2017-05-03 15:04:37.048 test[1064:39684] 3=========<NSThread: 0x60800007bfc0>{number = 5, name = (null)}
2017-05-03 15:04:37.048 test[1064:39685] 2=========<NSThread: 0x60800007bc00>{number = 4, name = (null)}
2017-05-03 15:04:37.048 test[1064:39690] 1=========<NSThread: 0x60800007bd00>{number = 3, name = (null)}
2017-05-03 15:04:37.049 test[1064:39684] 3=========<NSThread: 0x60800007bfc0>{number = 5, name = (null)}

開啟了多個新線程濒憋，并且在各自的新線程中執(zhí)行
任務(wù)交替著同時執(zhí)行
不會阻塞當(dāng)前線程

串行隊列+同步執(zhí)行

- (void)test {
    NSLog(@"=============begin") ;
    dispatch_queue_t myQueue = dispatch_queue_create("com.appress.myQueue",nil) ;
    dispatch_sync(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"1=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_sync(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"2=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_sync(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"3=========%@",[NSThread currentThread]) ;
        }
    }) ;
    NSLog(@"=============end") ;
}

打印結(jié)果為：

2017-05-03 15:10:33.497 test[1133:50233] =============begin
2017-05-03 15:10:33.497 test[1133:50233] 1=========<NSThread: 0x608000063800>{number = 1, name = main}
2017-05-03 15:10:33.498 test[1133:50233] 1=========<NSThread: 0x608000063800>{number = 1, name = main}
2017-05-03 15:10:33.498 test[1133:50233] 2=========<NSThread: 0x608000063800>{number = 1, name = main}
2017-05-03 15:10:33.498 test[1133:50233] 2=========<NSThread: 0x608000063800>{number = 1, name = main}
2017-05-03 15:10:33.499 test[1133:50233] 3=========<NSThread: 0x608000063800>{number = 1, name = main}
2017-05-03 15:10:33.499 test[1133:50233] 3=========<NSThread: 0x608000063800>{number = 1, name = main}
2017-05-03 15:10:33.499 test[1133:50233] =============end

不會開啟新線程，而是在當(dāng)前線程執(zhí)行
任務(wù)按照順序一個一個執(zhí)行
會阻塞當(dāng)前線程

串行隊列+異步執(zhí)行

- (void)test {
    NSLog(@"=============begin") ;
    dispatch_queue_t myQueue = dispatch_queue_create("com.appress.myQueue",nil) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"1=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"2=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"3=========%@",[NSThread currentThread]) ;
        }
    }) ;
    NSLog(@"=============end") ;
}

打印結(jié)果為：

2017-05-03 15:13:35.786 test[1168:56495] =============begin
2017-05-03 15:13:35.787 test[1168:56495] =============end
2017-05-03 15:13:35.787 test[1168:56601] 1=========<NSThread: 0x608000270200>{number = 3, name = (null)}
2017-05-03 15:13:35.787 test[1168:56601] 1=========<NSThread: 0x608000270200>{number = 3, name = (null)}
2017-05-03 15:13:35.787 test[1168:56601] 2=========<NSThread: 0x608000270200>{number = 3, name = (null)}
2017-05-03 15:13:35.787 test[1168:56601] 2=========<NSThread: 0x608000270200>{number = 3, name = (null)}
2017-05-03 15:13:35.788 test[1168:56601] 3=========<NSThread: 0x608000270200>{number = 3, name = (null)}
2017-05-03 15:13:35.788 test[1168:56601] 3=========<NSThread: 0x608000270200>{number = 3, name = (null)}

開啟了一個新線程陶夜，所有任務(wù)都在該新線程中執(zhí)行
任務(wù)按照順序一個一個執(zhí)行
不會阻塞當(dāng)前線程

主隊列+同步執(zhí)行

NSLog(@"=============begin") ;
    dispatch_queue_t myQueue = dispatch_get_main_queue() ;
    dispatch_sync(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"1=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_sync(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"2=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_sync(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"3=========%@",[NSThread currentThread]) ;
        }
    }) ;
    NSLog(@"=============end") ;

如果在主線程中采用該方式會出現(xiàn)互等卡住的情況凛驮。

在子線程中執(zhí)行的打印結(jié)果為：

2017-05-03 15:34:40.630 test[1279:89558] =============begin
2017-05-03 15:34:40.634 test[1279:89501] 1=========<NSThread: 0x60000006e3c0>{number = 1, name = main}
2017-05-03 15:34:40.635 test[1279:89501] 1=========<NSThread: 0x60000006e3c0>{number = 1, name = main}
2017-05-03 15:34:40.636 test[1279:89501] 2=========<NSThread: 0x60000006e3c0>{number = 1, name = main}
2017-05-03 15:34:40.636 test[1279:89501] 2=========<NSThread: 0x60000006e3c0>{number = 1, name = main}
2017-05-03 15:34:40.636 test[1279:89501] 3=========<NSThread: 0x60000006e3c0>{number = 1, name = main}
2017-05-03 15:34:40.636 test[1279:89501] 3=========<NSThread: 0x60000006e3c0>{number = 1, name = main}
2017-05-03 15:34:40.637 test[1279:89558] =============end

在主線程中執(zhí)行
任務(wù)按照順序一個一個執(zhí)行
會阻塞當(dāng)前線程

主隊列+異步執(zhí)行

- (void)test {
    NSLog(@"=============begin") ;
    dispatch_queue_t myQueue = dispatch_get_main_queue() ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"1=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"2=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 2; i++) {
            NSLog(@"3=========%@",[NSThread currentThread]) ;
        }
    }) ;
    NSLog(@"=============end") ;
}

打印結(jié)果為：

2017-05-03 15:36:10.336 test[1312:93448] =============begin
2017-05-03 15:36:10.337 test[1312:93448] =============end
2017-05-03 15:36:10.347 test[1312:93448] 1=========<NSThread: 0x600000064c80>{number = 1, name = main}
2017-05-03 15:36:10.348 test[1312:93448] 1=========<NSThread: 0x600000064c80>{number = 1, name = main}
2017-05-03 15:36:10.352 test[1312:93448] 2=========<NSThread: 0x600000064c80>{number = 1, name = main}
2017-05-03 15:36:10.358 test[1312:93448] 2=========<NSThread: 0x600000064c80>{number = 1, name = main}
2017-05-03 15:36:10.359 test[1312:93448] 3=========<NSThread: 0x600000064c80>{number = 1, name = main}
2017-05-03 15:36:10.359 test[1312:93448] 3=========<NSThread: 0x600000064c80>{number = 1, name = main}

在主線程中執(zhí)行
任務(wù)按照順序一個一個執(zhí)行
不會阻塞當(dāng)前線程

總結(jié)如下：

隊列	并行隊列	串行隊列	主隊列
同步（sync）	沒有開啟新線程，串行執(zhí)行任務(wù)	沒有開啟新線程条辟，串行執(zhí)行任務(wù)	沒有開啟新線程黔夭，串行執(zhí)行任務(wù)
異步（async）	有開啟新線程，并發(fā)執(zhí)行任務(wù)	有開啟新線程羽嫡，串行執(zhí)行任務(wù)	沒有開啟新線程本姥，串行執(zhí)行任務(wù)

當(dāng)任務(wù)隊列為非主隊列時，只有異步執(zhí)行才會開啟新線程杭棵。如果是并發(fā)隊列,會開啟多條線程婚惫，如果是串行隊列, 只會開啟一條線程。其他情況下(包括主隊列) 都不會開啟新線程,并且是串行執(zhí)行任務(wù)。

GCD的其他使用

GCD 柵欄函數(shù)

在異步執(zhí)行任務(wù)的過程中辰妙，有時候需要控制任務(wù)執(zhí)行的順序：在第一組任務(wù)執(zhí)行完成后再執(zhí)行第二組任務(wù)，可以通過GCD的柵欄函數(shù)dispatch_barrier_async來實現(xiàn)甫窟。當(dāng)柵欄函數(shù)執(zhí)行完成后才會執(zhí)行后面的任務(wù)密浑。

使用

添加?xùn)艡诤瘮?shù)前：

- (void)test {
    NSLog(@"=============begin") ;
    dispatch_queue_t myQueue = dispatch_queue_create("com.appress.myQueue",DISPATCH_QUEUE_CONCURRENT) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 3; i++) {
            NSLog(@"1=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 3; i++) {
            NSLog(@"2=========%@",[NSThread currentThread]) ;
        }
    }) ;
//    dispatch_barrier_async(myQueue, ^{
//        NSLog(@"++++++++++++++++++++++++++++++++++++++++") ;
//    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 3; i++) {
            NSLog(@"3=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 3; i++) {
            NSLog(@"4=========%@",[NSThread currentThread]) ;
        }
    }) ;
    NSLog(@"=============end") ;
}

打印結(jié)果為：

2017-05-08 15:37:00.970 test[14150:286911] =============begin
2017-05-08 15:37:00.970 test[14150:286911] =============end
2017-05-08 15:37:00.970 test[14150:286950] 2=========<NSThread: 0x60000026b480>{number = 4, name = (null)}
2017-05-08 15:37:00.970 test[14150:286951] 1=========<NSThread: 0x608000267680>{number = 3, name = (null)}
2017-05-08 15:37:00.970 test[14150:286971] 4=========<NSThread: 0x60000026bac0>{number = 6, name = (null)}
2017-05-08 15:37:00.970 test[14150:286953] 3=========<NSThread: 0x60000026b4c0>{number = 5, name = (null)}
2017-05-08 15:37:00.971 test[14150:286950] 2=========<NSThread: 0x60000026b480>{number = 4, name = (null)}
2017-05-08 15:37:00.971 test[14150:286951] 1=========<NSThread: 0x608000267680>{number = 3, name = (null)}
2017-05-08 15:37:00.971 test[14150:286971] 4=========<NSThread: 0x60000026bac0>{number = 6, name = (null)}
2017-05-08 15:37:00.971 test[14150:286953] 3=========<NSThread: 0x60000026b4c0>{number = 5, name = (null)}
2017-05-08 15:37:00.971 test[14150:286950] 2=========<NSThread: 0x60000026b480>{number = 4, name = (null)}
2017-05-08 15:37:00.971 test[14150:286951] 1=========<NSThread: 0x608000267680>{number = 3, name = (null)}
2017-05-08 15:37:00.972 test[14150:286953] 3=========<NSThread: 0x60000026b4c0>{number = 5, name = (null)}
2017-05-08 15:37:00.972 test[14150:286971] 4=========<NSThread: 0x60000026bac0>{number = 6, name = (null)}

添加?xùn)艡诤瘮?shù)后：

- (void)test {
    NSLog(@"=============begin") ;
    dispatch_queue_t myQueue = dispatch_queue_create("com.appress.myQueue",DISPATCH_QUEUE_CONCURRENT) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 3; i++) {
            NSLog(@"1=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 3; i++) {
            NSLog(@"2=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_barrier_async(myQueue, ^{
        NSLog(@"++++++++++++++++++++++++++++++++++++++++") ;
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 3; i++) {
            NSLog(@"3=========%@",[NSThread currentThread]) ;
        }
    }) ;
    dispatch_async(myQueue, ^{
        for(int i = 0; i < 3; i++) {
            NSLog(@"4=========%@",[NSThread currentThread]) ;
        }
    }) ;
    NSLog(@"=============end") ;
}

打印結(jié)果為：

2017-05-08 16:02:47.255 test[14241:316852] =============begin
2017-05-08 16:02:47.256 test[14241:316852] =============end
2017-05-08 16:02:47.256 test[14241:316986] 1=========<NSThread: 0x60000006f440>{number = 3, name = (null)}
2017-05-08 16:02:47.256 test[14241:316983] 2=========<NSThread: 0x60800006c2c0>{number = 4, name = (null)}
2017-05-08 16:02:47.256 test[14241:316986] 1=========<NSThread: 0x60000006f440>{number = 3, name = (null)}
2017-05-08 16:02:47.256 test[14241:316983] 2=========<NSThread: 0x60800006c2c0>{number = 4, name = (null)}
2017-05-08 16:02:47.256 test[14241:316986] 1=========<NSThread: 0x60000006f440>{number = 3, name = (null)}
2017-05-08 16:02:47.257 test[14241:316983] 2=========<NSThread: 0x60800006c2c0>{number = 4, name = (null)}
2017-05-08 16:02:47.257 test[14241:316983] ++++++++++++++++++++++++++++++++++++++++
2017-05-08 16:02:47.257 test[14241:316983] 3=========<NSThread: 0x60800006c2c0>{number = 4, name = (null)}
2017-05-08 16:02:47.257 test[14241:316986] 4=========<NSThread: 0x60000006f440>{number = 3, name = (null)}
2017-05-08 16:02:47.257 test[14241:316983] 3=========<NSThread: 0x60800006c2c0>{number = 4, name = (null)}
2017-05-08 16:02:47.257 test[14241:316986] 4=========<NSThread: 0x60000006f440>{number = 3, name = (null)}
2017-05-08 16:02:47.257 test[14241:316983] 3=========<NSThread: 0x60800006c2c0>{number = 4, name = (null)}
2017-05-08 16:02:47.258 test[14241:316986] 4=========<NSThread: 0x60000006f440>{number = 3, name = (null)}

注意

柵欄函數(shù)不能使用全局的并發(fā)隊列。

GCD的迭代

使用

dispatch_apply(迭代次數(shù), 線程隊列（并發(fā)隊列）, ^(size_t index索引) {
       執(zhí)行任務(wù) ;
}) ;

注意

開啟了子線程來執(zhí)行任務(wù)
迭代不是按照順序的

GCD隊列組

異步執(zhí)行多個耗時操作粗井，當(dāng)所有操作都執(zhí)行完畢后再執(zhí)行某一操作尔破。可以通過使用GCD隊列組來實現(xiàn)浇衬。

使用

NSLog(@"===============begin") ;
dispatch_group_t group = dispatch_group_create() ;
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) ;
dispatch_group_async(group, queue, ^{
    for(int i = 0 ; i < 4 ; i ++) {
        NSLog(@"1===============%@",[NSThread currentThread]) ;
    }
}) ;
dispatch_group_async(group, queue, ^{
    for(int i = 0 ; i < 4 ; i ++) {
        NSLog(@"2===============%@",[NSThread currentThread]) ;
    }
}) ;
dispatch_group_async(group, queue, ^{
    for(int i = 0 ; i < 4 ; i ++) {
        NSLog(@"3===============%@",[NSThread currentThread]) ;
    }
}) ;
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
    NSLog(@"===============end") ;
}) ;

打印結(jié)果為：

2017-08-08 13:36:21.124 GCD[3643:200121] ===============begin
2017-08-08 13:36:21.125 GCD[3643:200159] 1===============<NSThread: 0x60000007f2c0>{number = 3, name = (null)}
2017-08-08 13:36:21.125 GCD[3643:200156] 3===============<NSThread: 0x608000267100>{number = 5, name = (null)}
2017-08-08 13:36:21.125 GCD[3643:200157] 2===============<NSThread: 0x60800007cac0>{number = 4, name = (null)}
2017-08-08 13:36:21.125 GCD[3643:200159] 1===============<NSThread: 0x60000007f2c0>{number = 3, name = (null)}
2017-08-08 13:36:21.125 GCD[3643:200156] 3===============<NSThread: 0x608000267100>{number = 5, name = (null)}
2017-08-08 13:36:21.125 GCD[3643:200157] 2===============<NSThread: 0x60800007cac0>{number = 4, name = (null)}
2017-08-08 13:36:21.125 GCD[3643:200159] 1===============<NSThread: 0x60000007f2c0>{number = 3, name = (null)}
2017-08-08 13:36:21.125 GCD[3643:200156] 3===============<NSThread: 0x608000267100>{number = 5, name = (null)}
2017-08-08 13:36:21.126 GCD[3643:200157] 2===============<NSThread: 0x60800007cac0>{number = 4, name = (null)}
2017-08-08 13:36:21.126 GCD[3643:200159] 1===============<NSThread: 0x60000007f2c0>{number = 3, name = (null)}
2017-08-08 13:36:21.126 GCD[3643:200156] 3===============<NSThread: 0x608000267100>{number = 5, name = (null)}
2017-08-08 13:36:21.126 GCD[3643:200157] 2===============<NSThread: 0x60800007cac0>{number = 4, name = (null)}
2017-08-08 13:36:21.132 GCD[3643:200121] ===============end

如果dispatch_group_async的操作中有延時回調(diào)懒构，那么在所有回調(diào)完成前就會執(zhí)行dispatch_group_notify。

typedef void (^resultBlock) () ;
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"===============begin") ;
    dispatch_group_t group = dispatch_group_create() ;
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) ;
    dispatch_group_async(group, queue, ^{
        [self testWithBlock:^{
            for(int i = 0 ; i < 4 ; i ++) {
                NSLog(@"1===============%@",[NSThread currentThread]) ;
            }
        }] ;
    }) ;
    dispatch_group_async(group, queue, ^{
        [self testWithBlock:^{
            for(int i = 0 ; i < 4 ; i ++) {
                NSLog(@"2===============%@",[NSThread currentThread]) ;
            }
        }] ;

    }) ;
    dispatch_group_async(group, queue, ^{
        [self testWithBlock:^{
            for(int i = 0 ; i < 4 ; i ++) {
                NSLog(@"3===============%@",[NSThread currentThread]) ;
            }
        }] ;
    }) ;
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"===============end") ;
    }) ;
}

- (void)testWithBlock:(resultBlock)block {
    dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0*NSEC_PER_SEC)) ;
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT) ;
    dispatch_after(time, queue, ^{
        block() ;
    }) ;
}

打印結(jié)果為:

2017-08-08 14:40:25.811 GCD[16467:291922] ===============begin
2017-08-08 14:40:26.048 GCD[16467:291922] ===============end
2017-08-08 14:40:28.007 GCD[16467:291980] 1===============<NSThread: 0x60000007c900>{number = 3, name = (null)}
2017-08-08 14:40:28.007 GCD[16467:291979] 3===============<NSThread: 0x608000262100>{number = 4, name = (null)}
2017-08-08 14:40:28.007 GCD[16467:291982] 2===============<NSThread: 0x60000007c340>{number = 5, name = (null)}
2017-08-08 14:40:28.008 GCD[16467:291979] 3===============<NSThread: 0x608000262100>{number = 4, name = (null)}
2017-08-08 14:40:28.008 GCD[16467:291980] 1===============<NSThread: 0x60000007c900>{number = 3, name = (null)}
2017-08-08 14:40:28.008 GCD[16467:291982] 2===============<NSThread: 0x60000007c340>{number = 5, name = (null)}
2017-08-08 14:40:28.008 GCD[16467:291979] 3===============<NSThread: 0x608000262100>{number = 4, name = (null)}
2017-08-08 14:40:28.008 GCD[16467:291980] 1===============<NSThread: 0x60000007c900>{number = 3, name = (null)}
2017-08-08 14:40:28.008 GCD[16467:291982] 2===============<NSThread: 0x60000007c340>{number = 5, name = (null)}
2017-08-08 14:40:28.009 GCD[16467:291979] 3===============<NSThread: 0x608000262100>{number = 4, name = (null)}
2017-08-08 14:40:28.009 GCD[16467:291980] 1===============<NSThread: 0x60000007c900>{number = 3, name = (null)}
2017-08-08 14:40:28.009 GCD[16467:291982] 2===============<NSThread: 0x60000007c340>{number = 5, name = (null)}

通過dispatch_group_enter(group)和dispatch_group_leave(group)的配合使用來解決這個問題耘擂。

typedef void (^resultBlock) () ;

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"===============begin") ;
    dispatch_group_t group = dispatch_group_create() ;
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) ;
    dispatch_group_enter(group) ;
    dispatch_group_async(group, queue, ^{
        [self testWithBlock:^{
            for(int i = 0 ; i < 4 ; i ++) {
                NSLog(@"1===============%@",[NSThread currentThread]) ;
            }
            dispatch_group_leave(group) ;
        }] ;
    }) ;
    dispatch_group_enter(group) ;
    dispatch_group_async(group, queue, ^{
        [self testWithBlock:^{
            for(int i = 0 ; i < 4 ; i ++) {
                NSLog(@"2===============%@",[NSThread currentThread]) ;
            }
            dispatch_group_leave(group) ;
        }] ;

    }) ;
    dispatch_group_enter(group) ;
    dispatch_group_async(group, queue, ^{
        [self testWithBlock:^{
            for(int i = 0 ; i < 4 ; i ++) {
                NSLog(@"3===============%@",[NSThread currentThread]) ;
            }
            dispatch_group_leave(group) ;
        }] ;
    }) ;
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"===============end") ;
    }) ;
}

- (void)testWithBlock:(resultBlock)block {
    dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0*NSEC_PER_SEC)) ;
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT) ;
    dispatch_after(time, queue, ^{
        block() ;
    }) ;
}

@end

打印結(jié)果為：

2017-08-08 15:03:07.867 GCD[16548:311040] ===============begin
2017-08-08 15:03:09.868 GCD[16548:311101] 2===============<NSThread: 0x6000000773c0>{number = 5, name = (null)}
2017-08-08 15:03:09.868 GCD[16548:311098] 3===============<NSThread: 0x60000007ab40>{number = 3, name = (null)}
2017-08-08 15:03:09.868 GCD[16548:311099] 1===============<NSThread: 0x608000071d80>{number = 4, name = (null)}
2017-08-08 15:03:09.869 GCD[16548:311101] 2===============<NSThread: 0x6000000773c0>{number = 5, name = (null)}
2017-08-08 15:03:09.869 GCD[16548:311098] 3===============<NSThread: 0x60000007ab40>{number = 3, name = (null)}
2017-08-08 15:03:09.869 GCD[16548:311099] 1===============<NSThread: 0x608000071d80>{number = 4, name = (null)}
2017-08-08 15:03:09.869 GCD[16548:311101] 2===============<NSThread: 0x6000000773c0>{number = 5, name = (null)}
2017-08-08 15:03:09.869 GCD[16548:311098] 3===============<NSThread: 0x60000007ab40>{number = 3, name = (null)}
2017-08-08 15:03:09.869 GCD[16548:311099] 1===============<NSThread: 0x608000071d80>{number = 4, name = (null)}
2017-08-08 15:03:09.869 GCD[16548:311101] 2===============<NSThread: 0x6000000773c0>{number = 5, name = (null)}
2017-08-08 15:03:09.870 GCD[16548:311098] 3===============<NSThread: 0x60000007ab40>{number = 3, name = (null)}
2017-08-08 15:03:09.870 GCD[16548:311099] 1===============<NSThread: 0x608000071d80>{number = 4, name = (null)}
2017-08-08 15:03:09.870 GCD[16548:311040] ===============end

通過這種方法可以解決諸如：多個網(wǎng)絡(luò)請求全部完成以后再進(jìn)行某項操作的問題胆剧。

最后編輯于：2017.12.10 00:24:48

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GCD多線程應(yīng)用

概念

任務(wù)

隊列

GCD的多線程使用

使用步驟

使用方式

GCD的其他使用

GCD 柵欄函數(shù)

使用

注意

GCD的迭代

使用

注意

GCD隊列組

使用

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