iOS 多线程（GCD使用指南）Dispatch Queue是用来执行任务的队列，是GCD中最基本的元素之一。图示： S

什么是GCD

Grand Central Dispatch (GCD) 是 Apple 开发的一个多核编程的解决方法。该方法在 Mac OS X 10.6 雪豹中首次推出，并随后被引入到了 iOS4.0 中。GCD 是一个替代诸如 NSThread, NSOperationQueue, NSInvocationOperation 等技术的很高效和强大的技术。它为你提供了很多底层工具（比如队列和信号量），你可以组合这些工具来实现自己想要的多线程效果。

GCD API列表

API	说明
dispatch_sync()	同步执行
dispatch_async()	异步执行
dispatch_after()	延时执行
dispatch_once()	一次性执行
dispatch_apply()	提交队列
dispatch_queue_create()	创建队列
dispatch_group_create()	创建队列组
dispatch_group_enter() / dispatch_group_leave()	将队列组中的任务未执行完毕的任务数目加减1(两个函数要配合使用)
dispatch_group_notify()	监听队列组执行完毕
dispatch_group_wait()	设置等待时间(返回 0成功,1失败)
dispatch_semaphore_creat()	创建信号量
dispatch_barrier_sync()	同步栅栏函数
dispatch_barrier_async()	异步栅栏函数

GCD中的队列

Dispatch Queue
Dispatch Queue是用来执行任务的队列，是GCD中最基本的元素之一。图示：

一张图片可以很直观地描述GCD与线程之间的关系：

两种Dispatch Queue

Dispatch Queue种类	说明
Serial Dispatch Queue(串行队列)	等待现在执行中处理结束
Concurrent Dispatch Queue(并发队列)	不等待现在执行中处理

Serial Dispatch Queue(串行队列): 假设把 任务1 任务2 任务3 任务4 四个任务依次加入到一个Serial Dispatch Queue中，这个Serial Dispatch Queue会创建一个线程，依次执行这四个任务。
Concurrent Dispatch Queue(并发队列): 假设把 任务1 任务2 任务3 任务4 四个任务依次加入到一个Concurrent Dispatch Queue中，这个Concurrent Dispatch Queue会创建多个线程，并发执行这四个任务。
图示：

Main Dispatch Queue(主队列)
是在主线程执行的dispatch queue, Main Dispatch Queue(主队列)是一个Serail Dispatch Queue(串行队列)。追加到Main Dispatch Queue(主队列)的处理在主线程的RunLoop中执行。一般将用户界面更新等必需要在主线程中执行的处理追加到Main Dispatch Queue(主队列)中。

名称	Dispatch Queue的种类	说明
Main Dispatch Queue	Serial Dispatch Queue	主线程执行

获取Main Dispatch Queue方法：

dispatch_queue_t mainDispatchQueue = dispatch_get_main_queue();

Global Dispatch Queue(全局并发队列)
是所有应用程序都能过使用的Concurrent Dispatch Queue(全局并发队列)。没有必要通过dispatch_queue_create函数逐个创建Concurrent Dispatch Queue(并发队列)，只要获取Global Dispatch Queue(全局并发队列)使用即可。Global Dispatch Queue(全局并发队列)有四个优先级

名称	Dispatch Queue的种类	说明
Global Dispatch Queue(High Priority)	Concurrent Dispatch queue	执行优先级：高(最高)
Global Dispatch Queue(Default Priority)	Concurrent Dispatch queue	执行优先级：默认
Global Dispatch Queue(Low Priority)	Concurrent Dispatch queue	执行优先级：低
Global Dispatch Queue(Background Priority)	Concurrent Dispatch queue	执行优先级：后台

获取Global Dispatch Queue方法：

dispatch_queue_t globalDispatchQueueHigh = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);

dispatch_queue_t globalDispatchQueueDefault = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_queue_t globalDispatchQueueLow = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);

dispatch_queue_t globalDispatchQueueBackground = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);

Main Dispatch Queue和Global Dispatch Queue的搭配使用

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    /**
     *  可并行处理的任务TODO
     */

    dispatch_async(dispatch_get_main_queue(), ^{
        /**
         *  主线程执行
         */
    });
});

GCD中队列与线程的搭配使用情况

同步函数_串行队列

(不会开启新线程,串行执行任务)

同步函数_并发队列

(不会开启新线程,并发执行任务失效!)

异步函数_串行队列

(开启新线程,串行执行任务)

异步函数_并发队列

(开启新线程,并发执行任务)

GCD实例代码

最基础的写法

//1:创建串行队列
dispatch_queue_t queue = dispatch_queue_create("Noah", DISPATCH_QUEUE_SERIAL);
//2:创建任务
dispatch_block_t taskBlock = ^{
    NSLog(@"%@",[NSThread currentThread]);
};
//3:利用函数把任务放入队列
dispatch_sync(queue, taskBlock);

主队列同步函数

/**
 主队列同步
 不会开线程
 */
- (void)mainSyncTest{
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        for (int i = 0; i<20; i++) {
            dispatch_sync(dispatch_get_main_queue(), ^{
                NSLog(@"%d-%@",i,[NSThread currentThread]);
            });
        }
    });

    NSLog(@"hello queue");
}

// 打印
2020-01-27 17:26:23.840677+0800 001---函数与队列[1750:96869] hello queue
2020-01-27 17:26:23.847367+0800 001---函数与队列[1750:96869] 0-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.847781+0800 001---函数与队列[1750:96869] 1-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.848094+0800 001---函数与队列[1750:96869] 2-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.848183+0800 001---函数与队列[1750:96869] 3-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.848259+0800 001---函数与队列[1750:96869] 4-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.848649+0800 001---函数与队列[1750:96869] 5-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.848740+0800 001---函数与队列[1750:96869] 6-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.848926+0800 001---函数与队列[1750:96869] 7-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.849003+0800 001---函数与队列[1750:96869] 8-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.849208+0800 001---函数与队列[1750:96869] 9-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.852510+0800 001---函数与队列[1750:96869] 10-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.852617+0800 001---函数与队列[1750:96869] 11-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.852688+0800 001---函数与队列[1750:96869] 12-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.852774+0800 001---函数与队列[1750:96869] 13-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.852859+0800 001---函数与队列[1750:96869] 14-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.852947+0800 001---函数与队列[1750:96869] 15-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.853023+0800 001---函数与队列[1750:96869] 16-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.853092+0800 001---函数与队列[1750:96869] 17-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.853186+0800 001---函数与队列[1750:96869] 18-<NSThread: 0x6000027dd3c0>{number = 1, name = main}
2020-01-27 17:26:23.853265+0800 001---函数与队列[1750:96869] 19-<NSThread: 0x6000027dd3c0>{number = 1, name = main}

主队列异步函数

/**
 主队列异步
 不会开线程 顺序
 */
- (void)mainAsyncTest{
    for (int i = 0; i<20; i++) {
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    NSLog(@"hello queue");
}

// 打印
2020-01-27 17:30:43.639916+0800 001---函数与队列[1775:98841] hello queue
2020-01-27 17:30:43.646298+0800 001---函数与队列[1775:98841] 0-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.646410+0800 001---函数与队列[1775:98841] 1-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.646486+0800 001---函数与队列[1775:98841] 2-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.646554+0800 001---函数与队列[1775:98841] 3-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.646638+0800 001---函数与队列[1775:98841] 4-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.646706+0800 001---函数与队列[1775:98841] 5-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.646768+0800 001---函数与队列[1775:98841] 6-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.646842+0800 001---函数与队列[1775:98841] 7-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.646907+0800 001---函数与队列[1775:98841] 8-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.646982+0800 001---函数与队列[1775:98841] 9-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.647046+0800 001---函数与队列[1775:98841] 10-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.647144+0800 001---函数与队列[1775:98841] 11-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.647326+0800 001---函数与队列[1775:98841] 12-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.647526+0800 001---函数与队列[1775:98841] 13-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.647701+0800 001---函数与队列[1775:98841] 14-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.647876+0800 001---函数与队列[1775:98841] 15-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.648045+0800 001---函数与队列[1775:98841] 16-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.648204+0800 001---函数与队列[1775:98841] 17-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.648363+0800 001---函数与队列[1775:98841] 18-<NSThread: 0x600003aea900>{number = 1, name = main}
2020-01-27 17:30:43.648511+0800 001---函数与队列[1775:98841] 19-<NSThread: 0x600003aea900>{number = 1, name = main}

全局队列异步函数

/**
 全局异步
 全局队列:一个并发队列
 */
- (void)globalAsyncTest{
    for (int i = 0; i<20; i++) {
        
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    
    NSLog(@"hello queue");
}

// 打印
2020-01-27 17:32:46.849803+0800 001---函数与队列[1796:100014] hello queue
2020-01-27 17:32:46.849839+0800 001---函数与队列[1796:100060] 0-<NSThread: 0x60000004db40>{number = 3, name = (null)}
2020-01-27 17:32:46.849841+0800 001---函数与队列[1796:100073] 1-<NSThread: 0x600000017400>{number = 4, name = (null)}
2020-01-27 17:32:46.849872+0800 001---函数与队列[1796:100061] 2-<NSThread: 0x60000004db00>{number = 5, name = (null)}
2020-01-27 17:32:46.849880+0800 001---函数与队列[1796:100059] 3-<NSThread: 0x60000005fb00>{number = 6, name = (null)}
2020-01-27 17:32:46.849917+0800 001---函数与队列[1796:100073] 6-<NSThread: 0x600000017400>{number = 4, name = (null)}
2020-01-27 17:32:46.849924+0800 001---函数与队列[1796:100060] 7-<NSThread: 0x60000004db40>{number = 3, name = (null)}
2020-01-27 17:32:46.849928+0800 001---函数与队列[1796:100058] 4-<NSThread: 0x600000074700>{number = 7, name = (null)}
2020-01-27 17:32:46.849950+0800 001---函数与队列[1796:100061] 9-<NSThread: 0x60000004db00>{number = 5, name = (null)}
2020-01-27 17:32:46.849964+0800 001---函数与队列[1796:100074] 5-<NSThread: 0x60000007c600>{number = 8, name = (null)}
2020-01-27 17:32:46.849974+0800 001---函数与队列[1796:100059] 10-<NSThread: 0x60000005fb00>{number = 6, name = (null)}
2020-01-27 17:32:46.850015+0800 001---函数与队列[1796:100075] 8-<NSThread: 0x600000064040>{number = 9, name = (null)}
2020-01-27 17:32:46.850033+0800 001---函数与队列[1796:100076] 11-<NSThread: 0x600000078280>{number = 10, name = (null)}
2020-01-27 17:32:46.850021+0800 001---函数与队列[1796:100073] 12-<NSThread: 0x600000017400>{number = 4, name = (null)}
2020-01-27 17:32:46.850065+0800 001---函数与队列[1796:100077] 13-<NSThread: 0x600000070340>{number = 11, name = (null)}
2020-01-27 17:32:46.850068+0800 001---函数与队列[1796:100078] 15-<NSThread: 0x60000004dec0>{number = 12, name = (null)}
2020-01-27 17:32:46.850096+0800 001---函数与队列[1796:100061] 17-<NSThread: 0x60000004db00>{number = 5, name = (null)}
2020-01-27 17:32:46.850107+0800 001---函数与队列[1796:100079] 16-<NSThread: 0x60000005fe00>{number = 13, name = (null)}
2020-01-27 17:32:46.850021+0800 001---函数与队列[1796:100060] 14-<NSThread: 0x60000004db40>{number = 3, name = (null)}
2020-01-27 17:32:46.850138+0800 001---函数与队列[1796:100080] 18-<NSThread: 0x600000078340>{number = 14, name = (null)}
2020-01-27 17:32:46.850161+0800 001---函数与队列[1796:100081] 19-<NSThread: 0x6000000640c0>{number = 15, name = (null)}

全局队列同步函数

/**
 全局同步
 全局队列:一个并发队列
 */
- (void)globalSyncTest{
    for (int i = 0; i<20; i++) {
        dispatch_sync(dispatch_get_global_queue(0, 0), ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    
    NSLog(@"hello queue");
}

// 打印
2020-01-27 17:34:19.755161+0800 001---函数与队列[1825:101279] 0-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755253+0800 001---函数与队列[1825:101279] 1-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755328+0800 001---函数与队列[1825:101279] 2-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755422+0800 001---函数与队列[1825:101279] 3-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755485+0800 001---函数与队列[1825:101279] 4-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755555+0800 001---函数与队列[1825:101279] 5-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755619+0800 001---函数与队列[1825:101279] 6-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755695+0800 001---函数与队列[1825:101279] 7-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755760+0800 001---函数与队列[1825:101279] 8-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755825+0800 001---函数与队列[1825:101279] 9-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755887+0800 001---函数与队列[1825:101279] 10-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.755949+0800 001---函数与队列[1825:101279] 11-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.763221+0800 001---函数与队列[1825:101279] 12-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.763318+0800 001---函数与队列[1825:101279] 13-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.763412+0800 001---函数与队列[1825:101279] 14-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.763468+0800 001---函数与队列[1825:101279] 15-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.763553+0800 001---函数与队列[1825:101279] 16-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.763615+0800 001---函数与队列[1825:101279] 17-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.763681+0800 001---函数与队列[1825:101279] 18-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.763744+0800 001---函数与队列[1825:101279] 19-<NSThread: 0x600003aa93c0>{number = 1, name = main}
2020-01-27 17:34:19.763795+0800 001---函数与队列[1825:101279] hello queue

同步队列并发函数

/**
 同步并发
 不开线程:就算并发出来,没有坑位接受,所以顺序执行
 */
- (void)concurrentSyncTest{

    //1:创建并发队列
    dispatch_queue_t queue = dispatch_queue_create("Noah", DISPATCH_QUEUE_CONCURRENT);
    for (int i = 0; i<20; i++) {
        dispatch_sync(queue, ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    
    NSLog(@"hello queue");
}

// 打印
2020-01-27 17:36:47.811986+0800 001---函数与队列[1846:102561] 0-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812081+0800 001---函数与队列[1846:102561] 1-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812152+0800 001---函数与队列[1846:102561] 2-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812213+0800 001---函数与队列[1846:102561] 3-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812280+0800 001---函数与队列[1846:102561] 4-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812340+0800 001---函数与队列[1846:102561] 5-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812396+0800 001---函数与队列[1846:102561] 6-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812456+0800 001---函数与队列[1846:102561] 7-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812526+0800 001---函数与队列[1846:102561] 8-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812588+0800 001---函数与队列[1846:102561] 9-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812649+0800 001---函数与队列[1846:102561] 10-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.812728+0800 001---函数与队列[1846:102561] 11-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.820467+0800 001---函数与队列[1846:102561] 12-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.820589+0800 001---函数与队列[1846:102561] 13-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.820703+0800 001---函数与队列[1846:102561] 14-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.820774+0800 001---函数与队列[1846:102561] 15-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.820867+0800 001---函数与队列[1846:102561] 16-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.820949+0800 001---函数与队列[1846:102561] 17-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.821044+0800 001---函数与队列[1846:102561] 18-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.821108+0800 001---函数与队列[1846:102561] 19-<NSThread: 0x600000cd93c0>{number = 1, name = main}
2020-01-27 17:36:47.821180+0800 001---函数与队列[1846:102561] hello queue

异步队列并发函数

/**
 异步并发
 一次多个 没有顺序
 开线程
 */
- (void)concurrentAsyncTest{
    //1:创建并发队列
    dispatch_queue_t queue = dispatch_queue_create("Noah", DISPATCH_QUEUE_CONCURRENT);
    for (int i = 0; i<20; i++) {
        dispatch_async(queue, ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    
    NSLog(@"hello queue");
    
}

// 打印
2020-01-27 17:44:03.551880+0800 001---函数与队列[1878:104767] hello queue
2020-01-27 17:44:03.551943+0800 001---函数与队列[1878:104812] 0-<NSThread: 0x6000005797c0>{number = 3, name = (null)}
2020-01-27 17:44:03.551945+0800 001---函数与队列[1878:104814] 3-<NSThread: 0x6000005695c0>{number = 6, name = (null)}
2020-01-27 17:44:03.551950+0800 001---函数与队列[1878:104813] 1-<NSThread: 0x60000050afc0>{number = 4, name = (null)}
2020-01-27 17:44:03.551951+0800 001---函数与队列[1878:104825] 4-<NSThread: 0x600000543a00>{number = 7, name = (null)}
2020-01-27 17:44:03.551951+0800 001---函数与队列[1878:104815] 2-<NSThread: 0x600000543a80>{number = 5, name = (null)}
2020-01-27 17:44:03.551984+0800 001---函数与队列[1878:104826] 5-<NSThread: 0x60000050af40>{number = 8, name = (null)}
2020-01-27 17:44:03.552022+0800 001---函数与队列[1878:104812] 8-<NSThread: 0x6000005797c0>{number = 3, name = (null)}
2020-01-27 17:44:03.552033+0800 001---函数与队列[1878:104814] 9-<NSThread: 0x6000005695c0>{number = 6, name = (null)}
2020-01-27 17:44:03.552038+0800 001---\345\2072020-01-27 17:44:03.552075+0800 001---函数与队列[1878:104829] 10-<NSThread: 0x60000050af80>{number = 11, name = (null)}
2020-01-27 17:44:03.552083+0800 001---函数与队列[1878:104828] 7-<NSThread: 0x600000564340>{number = 10, name = (null)}
2020-01-27 17:44:03.552093+0800 001---函数与队列[1878:104826] 15-<NSThread: 0x60000050af40>{number = 8, name = (null)}
2020-01-27 17:44:03.552093+0800 001---函数与队列[1878:104815] 13-<NSThread: 0x600000543a80>{number = 5, name = (null)}
2020-01-27 17:44:03.552198+0800 001---函数与队列[1878:104834] 19-<NSThread: 0x600000575540>{number = 16, name = (null)}
2020-01-27 17:44:03.552113+0800 001---函数与队列[1878:104830] 14-<NSThread: 0x60000054c6c0>{number = 12, name = (null)}
2020-01-27 17:44:03.552135+0800 001---函数与队列[1878:104831] 16-<NSThread: 0x6000005643c0>{number = 13, name = (null)}
2020-01-27 17:44:03.552150+0800 001---函数与队列[1878:104832] 17-<NSThread: 0x600000569a00>{number = 14, name = (null)}
2020-01-27 17:44:03.552179+0800 001---函数与队列[1878:104833] 18-<NSThread: 0x600000543d80>{number = 15, name = (null)}
\275数与队列[1878:104827] 6-<NSThread: 0x60000054c640>{number = 9, name = (null)}
2020-01-27 17:44:03.552061+0800 001---函数与队列[1878:104813] 11-<NSThread: 0x60000050afc0>{number = 4, name = (null)}
2020-01-27 17:44:03.552063+0800 001---函数与队列[1878:104825] 12-<NSThread: 0x600000543a00>{number = 7, name = (null)}

串行队列异步函数

/**
 串行异步队列
 1:异步执行：会开启线程,顺序跟着耗时走
 */
- (void)serialAsyncTest{
    //1:创建串行队列
    dispatch_queue_t queue = dispatch_queue_create("Noah", DISPATCH_QUEUE_SERIAL);
    for (int i = 0; i<20; i++) {
        dispatch_async(queue, ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    
    NSLog(@"hello queue");
    
}
// 打印
2020-01-27 17:47:12.046872+0800 001---函数与队列[1896:106036] hello queue
2020-01-27 17:47:12.046903+0800 001---函数与队列[1896:106075] 0-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.046981+0800 001---函数与队列[1896:106075] 1-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047066+0800 001---函数与队列[1896:106075] 2-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047141+0800 001---函数与队列[1896:106075] 3-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047218+0800 001---函数与队列[1896:106075] 4-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047319+0800 001---函数与队列[1896:106075] 5-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047390+0800 001---函数与队列[1896:106075] 6-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047531+0800 001---函数与队列[1896:106075] 7-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047612+0800 001---函数与队列[1896:106075] 8-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047705+0800 001---函数与队列[1896:106075] 9-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047799+0800 001---函数与队列[1896:106075] 10-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.047876+0800 001---函数与队列[1896:106075] 11-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.056948+0800 001---函数与队列[1896:106075] 12-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.057028+0800 001---函数与队列[1896:106075] 13-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.057104+0800 001---函数与队列[1896:106075] 14-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.057165+0800 001---函数与队列[1896:106075] 15-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.057237+0800 001---函数与队列[1896:106075] 16-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.057312+0800 001---函数与队列[1896:106075] 17-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.057394+0800 001---函数与队列[1896:106075] 18-<NSThread: 0x600003450900>{number = 3, name = (null)}
2020-01-27 17:47:12.057469+0800 001---函数与队列[1896:106075] 19-<NSThread: 0x600003450900>{number = 3, name = (null)}

串行队列同步函数

/**
 串行同步队列
 1:同步执行：一行一行代码从上向下执行，当前代码不执行完成，不会执行后续代码 同步不会开启线程
 2:串行队列：一个一个的调度任务，前一个任务没有执行完成，不会调度后面的任务
 */
- (void)serialSyncTest{
    //1:创建串行队列
    dispatch_queue_t queue = dispatch_queue_create("Noah", DISPATCH_QUEUE_SERIAL);
    for (int i = 0; i<20; i++) {
        dispatch_sync(queue, ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    
    NSLog(@"hello queue");

}

// 打印
2020-01-27 17:48:54.224033+0800 001---函数与队列[1920:107306] 0-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224142+0800 001---函数与队列[1920:107306] 1-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224214+0800 001---函数与队列[1920:107306] 2-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224270+0800 001---函数与队列[1920:107306] 3-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224340+0800 001---函数与队列[1920:107306] 4-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224398+0800 001---函数与队列[1920:107306] 5-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224460+0800 001---函数与队列[1920:107306] 6-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224515+0800 001---函数与队列[1920:107306] 7-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224583+0800 001---函数与队列[1920:107306] 8-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224644+0800 001---函数与队列[1920:107306] 9-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224712+0800 001---函数与队列[1920:107306] 10-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224774+0800 001---函数与队列[1920:107306] 11-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.224833+0800 001---函数与队列[1920:107306] 12-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.232531+0800 001---函数与队列[1920:107306] 13-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.232614+0800 001---函数与队列[1920:107306] 14-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.232682+0800 001---函数与队列[1920:107306] 15-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.232741+0800 001---函数与队列[1920:107306] 16-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.232820+0800 001---函数与队列[1920:107306] 17-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.232890+0800 001---函数与队列[1920:107306] 18-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.232948+0800 001---函数与队列[1920:107306] 19-<NSThread: 0x6000012ae940>{number = 1, name = main}
2020-01-27 17:48:54.233001+0800 001---函数与队列[1920:107306] hello queue

dispatch_after使用

/**
 延迟测试
 */
- (void)delayDemo{
    
    //NSEC_PER_SEC : 1000000000ull 纳秒每秒 0.0000001 可以这么做参数
    dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC));
    //串行队列来测试 延迟的方法是不是异步的!
    dispatch_queue_t queue = dispatch_queue_create("com.lg.cn", DISPATCH_QUEUE_SERIAL);
    dispatch_after(time, queue, ^{
        NSLog(@"延迟打印");
    });
    NSLog(@"打印完了?");
}

//打印
2020-01-27 19:38:24.727940+0800 005---GCD进阶使用(下)[2216:130497] 打印完了?
2020-01-27 19:38:25.816560+0800 005---GCD进阶使用(下)[2216:130584] 延迟打印

dispatch_once使用

/**
 单例
 */
+(instancetype)shareManager{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [[self alloc] init];
    });
    return instance;
}

dispatch_group_async使用

/**
 调度组测试
 */
- (void)groupDemo{
    
    //创建调度组
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_queue_t queue1 = dispatch_queue_create("com.nh.cn", DISPATCH_QUEUE_CONCURRENT);

    // SIGNAL
    dispatch_group_async(group, queue, ^{
        NSString *logoStr = @"https://dss0.bdstatic.com/5aV1bjqh_Q23odCf/static/superman/img/logo_top-e3b63a0b1b.png";
        NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:logoStr]];
        UIImage *image = [UIImage imageWithData:data];
        [self.mArray addObject:image];
    });
    
    dispatch_group_async(group, queue1, ^{

        // afn --- sdk : queue: com.afn.cn
        NSString *logoStr = @"https://dss0.bdstatic.com/5aV1bjqh_Q23odCf/static/superman/img/logo_top-e3b63a0b1b.png";
        NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:logoStr]];
        UIImage *image = [UIImage imageWithData:data];
        [self.mArray addObject:image];

    });
    
    
    __block UIImage *newImage = nil;
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"数组个数:%ld",self.mArray.count);
    });

}

// 打印
2020-01-27 20:24:30.544956+0800 005---GCD进阶使用(下)[2546:203237] 数组个数:2

调度组内部方法使用

/**
 调度组内部方法 enter - leave
 */
- (void)groupDemo2{
    
    // 问题: 如果 dispatch_group_enter 多 dispatch_group_leave 不会调用通知
    // dispatch_group_enter 少 dispatch_group_leave  奔溃
    // 成对存在
    
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_group_t group = dispatch_group_create();
    
    dispatch_group_enter(group);
    
    // dispatch_group_async -- 下节课的源码分析 --封装意思
    dispatch_async(queue, ^{
        NSLog(@"第一个走完了");
        dispatch_group_leave(group);
    });
    
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        NSLog(@"第二个走完了");
    });
    
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"所有任务完成,可以更新UI");
    });
}

// 打印
2020-01-27 20:24:49.213355+0800 005---GCD进阶使用(下)[2555:203694] 第一个走完了
2020-01-27 20:24:49.213363+0800 005---GCD进阶使用(下)[2555:203697] 第二个走完了

栅栏函数

在使用栅栏函数时.使用自定义队列才有意义,如果用的是串行队列或者系统提供的全局并发队列,这个栅栏函数的作用等同于一个同步函数的作用

// dispatch_barrier_sync
- (void)demo2{
    
    // 你全部下载完毕之后,我才能处理
    dispatch_queue_t concurrentQueue = dispatch_queue_create("noah", DISPATCH_QUEUE_CONCURRENT);

    // 全局 -- 堵塞
    // 系统GG  -- 设计
    // 这里要注意，如果用的是全局队列，使用栅栏函数是无效的
//    dispatch_queue_t concurrentQueue = dispatch_get_global_queue(0, 0);

    /* 1.异步函数 */
    dispatch_async(concurrentQueue, ^{
        // 请求token -- 线程安全
        for (NSUInteger i = 0; i < 5; i++) {
            NSLog(@"download1-%zd-%@",i,[NSThread currentThread]);
        }
    });
//
    dispatch_async(concurrentQueue, ^{
        for (NSUInteger i = 0; i < 5; i++) {
            NSLog(@"download2-%zd-%@",i,[NSThread currentThread]);
        }
    });
    
    /* 2. 栅栏函数 */
    dispatch_barrier_sync(concurrentQueue, ^{
        NSLog(@"---------------------%@------------------------",[NSThread currentThread]);
    });
    NSLog(@"加载那么多,喘口气!!!");
    /* 3. 异步函数 */
    dispatch_async(concurrentQueue, ^{
        for (NSUInteger i = 0; i < 5; i++) {
            NSLog(@"日常处理3-%zd-%@",i,[NSThread currentThread]);
        }
    });
    NSLog(@"************起来干!!");
    
    dispatch_async(concurrentQueue, ^{
        for (NSUInteger i = 0; i < 5; i++) {
            NSLog(@"日常处理4-%zd-%@",i,[NSThread currentThread]);
        }
    });
    
}

 // 打印
2020-01-27 20:56:33.782415+0800 004--GCD进阶使用[2824:318070] download1-0-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.782420+0800 004--GCD进阶使用[2824:318073] download2-0-<NSThread: 0x600003974240>{number = 4, name = (null)}
2020-01-27 20:56:33.782515+0800 004--GCD进阶使用[2824:318070] download1-1-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.782521+0800 004--GCD进阶使用[2824:318073] download2-1-<NSThread: 0x600003974240>{number = 4, name = (null)}
2020-01-27 20:56:33.782599+0800 004--GCD进阶使用[2824:318070] download1-2-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.782609+0800 004--GCD进阶使用[2824:318073] download2-2-<NSThread: 0x600003974240>{number = 4, name = (null)}
2020-01-27 20:56:33.782659+0800 004--GCD进阶使用[2824:318070] download1-3-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.782694+0800 004--GCD进阶使用[2824:318073] download2-3-<NSThread: 0x600003974240>{number = 4, name = (null)}
2020-01-27 20:56:33.782755+0800 004--GCD进阶使用[2824:318070] download1-4-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.782759+0800 004--GCD进阶使用[2824:318073] download2-4-<NSThread: 0x600003974240>{number = 4, name = (null)}
2020-01-27 20:56:33.782938+0800 004--GCD进阶使用[2824:318033] ---------------------<NSThread: 0x600003902940>{number = 1, name = main}------------------------
2020-01-27 20:56:33.783020+0800 004--GCD进阶使用[2824:318033] 加载那么多,喘口气!!!
2020-01-27 20:56:33.783106+0800 004--GCD进阶使用[2824:318033] ************起来干!!
2020-01-27 20:56:33.783135+0800 004--GCD进阶使用[2824:318070] 日常处理3-0-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.783204+0800 004--GCD进阶使用[2824:318073] 日常处理4-0-<NSThread: 0x600003974240>{number = 4, name = (null)}
2020-01-27 20:56:33.783258+0800 004--GCD进阶使用[2824:318070] 日常处理3-1-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.783343+0800 004--GCD进阶使用[2824:318073] 日常处理4-1-<NSThread: 0x600003974240>{number = 4, name = (null)}
2020-01-27 20:56:33.792221+0800 004--GCD进阶使用[2824:318070] 日常处理3-2-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.792238+0800 004--GCD进阶使用[2824:318073] 日常处理4-2-<NSThread: 0x600003974240>{number = 4, name = (null)}
2020-01-27 20:56:33.792311+0800 004--GCD进阶使用[2824:318070] 日常处理3-3-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.792325+0800 004--GCD进阶使用[2824:318073] 日常处理4-3-<NSThread: 0x600003974240>{number = 4, name = (null)}
2020-01-27 20:56:33.792383+0800 004--GCD进阶使用[2824:318070] 日常处理3-4-<NSThread: 0x60000398a480>{number = 3, name = (null)}
2020-01-27 20:56:33.792399+0800 004--GCD进阶使用[2824:318073] 日常处理4-4-<NSThread: 0x600003974240>{number = 4, name = (null)}

// dispatch_barrier_async函数
/**
 可变数组 线程不安全 解决办法
 */
- (void)demo3{
    
    // 顺序执行
    // 线程安全
    
    dispatch_queue_t concurrentQueue = dispatch_queue_create("cooci", DISPATCH_QUEUE_CONCURRENT);

    // signal -- 线程BUG
    for (int i = 0; i<2000; i++) {
        dispatch_async(concurrentQueue, ^{
            NSString *imageName = [NSString stringWithFormat:@"%d.jpg", (i % 10)];
            NSURL *url = [[NSBundle mainBundle] URLForResource:imageName withExtension:nil];
            NSData *data = [NSData dataWithContentsOfURL:url];
            UIImage *image = [UIImage imageWithData:data];
            // 这代码如果不加处理会导致崩溃，因为多条线程同时操作一块内存会导致崩溃，可以加锁，也可以使用异步栅栏函数去处理 
            //[self.mArray addObject:image];
            dispatch_barrier_async(concurrentQueue, ^{
                [self.mArray addObject:image];
            });
        });
    }
}

其实dispatch_barrier_async与dispatch_barrier_sync两者之间并没有很大的区别，如果用dispatch_barrier_async的话就不会堵塞，用dispatch_barrier_sync就会堵塞，主要看功能代码逻辑去选择用哪个函数，两者的功能是一样的

参考文章

【iOS】玩转 - GCD
GCD的API详解