iOS 多线程的简单理解（2） 队列 ：串行 ，并行，MainQueue，GlobalQueue

多线程队列是装载线程任务的队形结构。(系统以先进先出的方式调度队列中的任务执行 FIFO)。在GCD中有两种队列：

串行队列、并发队列。

队列 ：串行队列、并发队列，全局主对列，全局并发队列

2.1.  串行队列：线程只能依次有序的执行。

2.1.1 串行方法 1

- (void)SerialQueueOne{
     
    NSLog(@"串行1 start ：：：%@",[NSThread currentThread]);
    
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
    
    dispatch_sync(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"串行1   index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for (int i = 10; i < 13; i++) {
            NSLog(@"串行1   index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    NSLog(@"串行1 end ：：：%@",[NSThread currentThread]);
}

 执行结果：：：

2017-12-20 13:49:47.427330+0800 DeadThread[8972:2450330] 串行1 start ：：：<NSThread: 0x60800006ae80>{number = 1, name = main}
2017-12-20 13:49:47.427470+0800 DeadThread[8972:2450330] 串行1   index 0 ::: <NSThread: 0x60800006ae80>{number = 1, name = main}
2017-12-20 13:49:47.427567+0800 DeadThread[8972:2450330] 串行1   index 1 ::: <NSThread: 0x60800006ae80>{number = 1, name = main}
2017-12-20 13:49:47.427636+0800 DeadThread[8972:2450330] 串行1   index 2 ::: <NSThread: 0x60800006ae80>{number = 1, name = main}
2017-12-20 13:49:47.427696+0800 DeadThread[8972:2450330] 串行1   index 10 ::: <NSThread: 0x60800006ae80>{number = 1, name = main}
2017-12-20 13:49:47.427819+0800 DeadThread[8972:2450330] 串行1   index 11 ::: <NSThread: 0x60800006ae80>{number = 1, name = main}
2017-12-20 13:49:47.427893+0800 DeadThread[8972:2450330] 串行1   index 12 ::: <NSThread: 0x60800006ae80>{number = 1, name = main}
2017-12-20 13:49:47.427966+0800 DeadThread[8972:2450330] 串行1 end ：：：<NSThread: 0x60800006ae80>{number = 1, name = main}

 得到结果：：：

 1.代码顺序 执行；

2.1.2 串行方法 2

- (void)SerialQueueTwo{
    
    NSLog(@"串行2 start ：：：%@",[NSThread currentThread]);
    
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
    
   dispatch_async(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"串行2   index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 10; i < 13; i++) {
            NSLog(@"串行2   index %d ::: %@",i,[NSThread currentThread]);
        }
    });

       NSLog(@"串行2 end ：：：%@",[NSThread currentThread]); 
}

 执行结果：：：

2017-12-20 13:50:47.130380+0800 DeadThread[8993:2458517] 串行1 start ：：：<NSThread: 0x60c000071300>{number = 1, name = main}
2017-12-20 13:50:47.130533+0800 DeadThread[8993:2458517] 串行1   index 0 ::: <NSThread: 0x60c000071300>{number = 1, name = main}
2017-12-20 13:50:47.130648+0800 DeadThread[8993:2458517] 串行1   index 1 ::: <NSThread: 0x60c000071300>{number = 1, name = main}
2017-12-20 13:50:47.130724+0800 DeadThread[8993:2458517] 串行1   index 2 ::: <NSThread: 0x60c000071300>{number = 1, name = main}
2017-12-20 13:50:47.130896+0800 DeadThread[8993:2458517] 串行1   index 10 ::: <NSThread: 0x60c000071300>{number = 1, name = main}
2017-12-20 13:50:47.130979+0800 DeadThread[8993:2458517] 串行1   index 11 ::: <NSThread: 0x60c000071300>{number = 1, name = main}
2017-12-20 13:50:47.131057+0800 DeadThread[8993:2458517] 串行1   index 12 ::: <NSThread: 0x60c000071300>{number = 1, name = main}
2017-12-20 13:50:47.131130+0800 DeadThread[8993:2458517] 串行1 end ：：：<NSThread: 0x60c000071300>{number = 1, name = main}

 得到结果：：：

1.没有开启线程

2.代码顺序执行；

2.2 并发队列：线程可以同时一起进行执行。实际上是CPU在多条线程之间快速的切换。（并发功能只有在异步（dispatch_async）函数下才有效）

2.2.1 并发方法 1

- (void)concurrentQueueOne{
    
    NSLog(@"并发1 start ：：：%@",[NSThread currentThread]);

    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);

    dispatch_sync(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"并发1  index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_sync(queue, ^{
        for (int i = 10; i < 13; i++) {
            NSLog(@"并发1  index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    
    NSLog(@"并发1 end ：：：%@",[NSThread currentThread]);
}

 执行结果：：：

2017-12-20 13:52:37.606997+0800 DeadThread[9023:2470506] 并发1 start ：：：<NSThread: 0x608000261600>{number = 1, name = main}
2017-12-20 13:52:37.607130+0800 DeadThread[9023:2470506] 并发1  index 0 ::: <NSThread: 0x608000261600>{number = 1, name = main}
2017-12-20 13:52:37.607197+0800 DeadThread[9023:2470506] 并发1  index 1 ::: <NSThread: 0x608000261600>{number = 1, name = main}
2017-12-20 13:52:37.607447+0800 DeadThread[9023:2470506] 并发1  index 2 ::: <NSThread: 0x608000261600>{number = 1, name = main}
2017-12-20 13:52:37.607685+0800 DeadThread[9023:2470506] 并发1  index 10 ::: <NSThread: 0x608000261600>{number = 1, name = main}
2017-12-20 13:52:37.607891+0800 DeadThread[9023:2470506] 并发1  index 11 ::: <NSThread: 0x608000261600>{number = 1, name = main}
2017-12-20 13:52:37.608056+0800 DeadThread[9023:2470506] 并发1  index 12 ::: <NSThread: 0x608000261600>{number = 1, name = main}
2017-12-20 13:52:37.608190+0800 DeadThread[9023:2470506] 并发1 end ：：：<NSThread: 0x608000261600>{number = 1, name = main}

 得到结果：：：

1.线程顺序执行

2.2.2 并发方法 2

- (void)concurrentQueueTwo{
    
    NSLog(@"并发2 start ：：：%@",[NSThread currentThread]);
    
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
    
    dispatch_async(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"并发2  index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_async(queue, ^{
        for (int i = 10; i < 13; i++) {
            NSLog(@"并发2  index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    
    NSLog(@"并发2 end ：：：%@",[NSThread currentThread]);
}

 执行结果：：；

2017-12-20 13:56:45.573695+0800 DeadThread[9084:2492640] 并发2 start ：：：<NSThread: 0x604000077d80>{number = 1, name = main}
2017-12-20 13:56:45.573891+0800 DeadThread[9084:2492640] 并发2 end ：：：<NSThread: 0x604000077d80>{number = 1, name = main}
2017-12-20 13:56:45.573907+0800 DeadThread[9084:2492674] 并发2  index 0 ::: <NSThread: 0x60c000265a40>{number = 3, name = (null)}
2017-12-20 13:56:45.573908+0800 DeadThread[9084:2492675] 并发2  index 10 ::: <NSThread: 0x60400026f000>{number = 4, name = (null)}
2017-12-20 13:56:45.574283+0800 DeadThread[9084:2492674] 并发2  index 1 ::: <NSThread: 0x60c000265a40>{number = 3, name = (null)}
2017-12-20 13:56:45.574344+0800 DeadThread[9084:2492675] 并发2  index 11 ::: <NSThread: 0x60400026f000>{number = 4, name = (null)}
2017-12-20 13:56:45.574420+0800 DeadThread[9084:2492675] 并发2  index 12 ::: <NSThread: 0x60400026f000>{number = 4, name = (null)}
2017-12-20 13:56:45.574422+0800 DeadThread[9084:2492674] 并发2  index 2 ::: <NSThread: 0x60c000265a40>{number = 3, name = (null)}

 得到结果：：：

1.添加两个 任务代码块，开启两个线程；

2.子线程中代码 不是按顺序执行

2.3 全局主队列：：：：

2.3.1  主队列 同步 死锁

- (void)syncMain {
 
    NSLog(@"

**************主队列同步，放到主线程会死锁***************

");
 
    // 主队列
    dispatch_queue_t queue = dispatch_get_main_queue();
 
    dispatch_sync(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"主队列同步1   %@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"主队列同步2   %@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"主队列同步3   %@",[NSThread currentThread]);
        }
    });
}

 死锁原因：：：

    如果在主线程中运用主队列同步，也就是把任务放到了主线程的队列中。

    而同步对于任务是立刻执行的，那么当把第一个任务放进主队列时，它就会立马执行。

    可是主线程现在正在处理syncMain方法，任务需要等syncMain执行完才能执行。

    syncMain执行到第一个任务的时候，又要等第一个任务执行完才能往下执行第二个和第三个任务。

    这样syncMain方法和第一个任务就开始了互相等待，形成了死锁。

2.3.2  主队列 异步

- (void)asyncMain {
 
    NSLog(@"**************主队列异步***************");
 
    // 主队列
    dispatch_queue_t queue = dispatch_get_main_queue();
 
    dispatch_async(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"主队列异步1   %@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"主队列异步2   %@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"主队列异步3   %@",[NSThread currentThread]);
        }
    });
}

 执行结果：：：

2017-12-20 14:20:01.729412+0800 DeadThread[9257:2636939] **************主队列异步***************
2017-12-20 14:20:01.732208+0800 DeadThread[9257:2636939] 主队列异步1   <NSThread: 0x604000261080>{number = 1, name = main}
2017-12-20 14:20:01.732326+0800 DeadThread[9257:2636939] 主队列异步1   <NSThread: 0x604000261080>{number = 1, name = main}
2017-12-20 14:20:01.732456+0800 DeadThread[9257:2636939] 主队列异步1   <NSThread: 0x604000261080>{number = 1, name = main}
2017-12-20 14:20:01.732726+0800 DeadThread[9257:2636939] 主队列异步2   <NSThread: 0x604000261080>{number = 1, name = main}
2017-12-20 14:20:01.732931+0800 DeadThread[9257:2636939] 主队列异步2   <NSThread: 0x604000261080>{number = 1, name = main}
2017-12-20 14:20:01.733026+0800 DeadThread[9257:2636939] 主队列异步2   <NSThread: 0x604000261080>{number = 1, name = main}
2017-12-20 14:20:01.733128+0800 DeadThread[9257:2636939] 主队列异步3   <NSThread: 0x604000261080>{number = 1, name = main}
2017-12-20 14:20:01.733251+0800 DeadThread[9257:2636939] 主队列异步3   <NSThread: 0x604000261080>{number = 1, name = main}
2017-12-20 14:20:01.733502+0800 DeadThread[9257:2636939] 主队列异步3   <NSThread: 0x604000261080>{number = 1, name = main}

得到结果：：：

1. 主队列是个同步队列

2.4 全局并发队列

2.4.1

- (void)globalQueueOne{
    
    NSLog(@"global1 start ：：：%@",[NSThread currentThread]);
    
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
    
    dispatch_sync(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"global1  index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_sync(queue, ^{
        for (int i = 10; i < 13; i++) {
            NSLog(@"global1  index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    
    NSLog(@"global1 end ：：：%@",[NSThread currentThread]);
}

 执行结果：：：

2017-12-20 14:27:02.302953+0800 DeadThread[9352:2669397] global1 start ：：：<NSThread: 0x6000000655c0>{number = 1, name = main}
2017-12-20 14:27:02.303132+0800 DeadThread[9352:2669397] global1  index 0 ::: <NSThread: 0x6000000655c0>{number = 1, name = main}
2017-12-20 14:27:02.303230+0800 DeadThread[9352:2669397] global1  index 1 ::: <NSThread: 0x6000000655c0>{number = 1, name = main}
2017-12-20 14:27:02.303322+0800 DeadThread[9352:2669397] global1  index 2 ::: <NSThread: 0x6000000655c0>{number = 1, name = main}
2017-12-20 14:27:02.303397+0800 DeadThread[9352:2669397] global1  index 10 ::: <NSThread: 0x6000000655c0>{number = 1, name = main}
2017-12-20 14:27:02.303467+0800 DeadThread[9352:2669397] global1  index 11 ::: <NSThread: 0x6000000655c0>{number = 1, name = main}
2017-12-20 14:27:02.303557+0800 DeadThread[9352:2669397] global1  index 12 ::: <NSThread: 0x6000000655c0>{number = 1, name = main}
2017-12-20 14:27:02.303638+0800 DeadThread[9352:2669397] global1 end ：：：<NSThread: 0x6000000655c0>{number = 1, name = main}

2.4.2

- (void)globalQueueTwo{
    
    NSLog(@"global2 start ：：：%@",[NSThread currentThread]);
    
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
    
    dispatch_async(queue, ^{
        for (int i = 0; i < 3; i++) {
            NSLog(@"global2   index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_async(queue, ^{
        for (int i = 10; i < 13; i++) {
            NSLog(@"global2   index %d ::: %@",i,[NSThread currentThread]);
        }
    });
    
    NSLog(@"global2 end ：：：%@",[NSThread currentThread]);
}

 执行结果：：：

2017-12-20 14:28:27.498062+0800 DeadThread[9382:2678820] global2 start ：：：<NSThread: 0x600000076700>{number = 1, name = main}
2017-12-20 14:28:27.498208+0800 DeadThread[9382:2678820] global2 end ：：：<NSThread: 0x600000076700>{number = 1, name = main}
2017-12-20 14:28:27.498250+0800 DeadThread[9382:2679707] global2   index 0 ::: <NSThread: 0x60c0000779c0>{number = 3, name = (null)}
2017-12-20 14:28:27.498260+0800 DeadThread[9382:2679706] global2   index 10 ::: <NSThread: 0x60400007e800>{number = 4, name = (null)}
2017-12-20 14:28:27.498555+0800 DeadThread[9382:2679707] global2   index 1 ::: <NSThread: 0x60c0000779c0>{number = 3, name = (null)}
2017-12-20 14:28:27.498692+0800 DeadThread[9382:2679706] global2   index 11 ::: <NSThread: 0x60400007e800>{number = 4, name = (null)}
2017-12-20 14:28:27.498710+0800 DeadThread[9382:2679707] global2   index 2 ::: <NSThread: 0x60c0000779c0>{number = 3, name = (null)}
2017-12-20 14:28:27.498753+0800 DeadThread[9382:2679706] global2   index 12 ::: <NSThread: 0x60400007e800>{number = 4, name = (null)}
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原文地址：https://www.cnblogs.com/Bob-blogs/p/8073578.html