玩转 GCD
2016-06-02 本文已影响1179人
LuisX
玩转 GCD
GCD介绍
Grand Central Dispatch (GCD)是Apple开发的一个多核编程的解决方法
基于C语言，提供了非常多强大的函数
GCD和其他多线程技术方案，如NSThread，NSOperationQueue，NSInvocationOperation等相比，使用起来更加方便。
术语
同步 (Synchronous)
在当前线程中执行任务，不具备开启新线程的能力
提交的任务在执行完成后才会返回
同步函数: dispatch_sync()异步 (Asynchronous)
在新线程中执行任务，具备开启新线程的能力
提交的任务立刻返回，在后台队列中执行
异步函数: dispatch_async()串行 (Serial)
一个任务执行完毕后，再执行下一个任务
并发 (Concurrent)
多个任务同时执行(自动开启多个线程),
只有在异步函数下才有效
| 描述 | 说明 |
|---|---|
| queue | 队列 |
| main | 主队列 |
| global | 全局队列 |
| dispatch_queue_t | 描述队列 |
| dispatch_block_t | 描述任务 |
| dispatch_once_t | 描述一次性 |
| dispatch_time_t | 描述时间 |
| dispatch_group_t | 描述队列组 |
| dispatch_semaphore_t | 描述信号量 |
| 函数 | 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_async() | 提交任务到队列组 |
| 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) |
注意:
1.所有的执行都放到队列中(queue)，队列的特点是FIFO（先提交的先执行）
2.必须在主线程访问 UIKit 的类
3.并发队列只在异步函数下才有效
基本使用
NSLog(@"当前线程: %@", [NSThread currentThread]);
//获取主队列
dispatch_queue_t mainQueue = dispatch_get_main_queue();
//获取全局并发队列
dispatch_queue_t otherQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//同步函数(在当前线程中执行,不具备开启新线程的能力)
dispatch_sync(otherQueue, ^{
NSLog(@"同步 %@", [NSThread currentThread]);
});
//异步函数(在另一条线程中执行,具备开启新线程的能力)
dispatch_async(otherQueue, ^{
NSLog(@"异步 %@", [NSThread currentThread]);
});
//输出: 当前线程: <NSThread: 0x7f81bac06670>{number = 1, name = main}
//输出: 同步 <NSThread: 0x7f81bac06670>{number = 1, name = main}
//输出: 异步 <NSThread: 0x7f81bae35be0>{number = 3, name = (null)}
延时执行 dispatch_after()
dispatch_after()延迟一段时间把一项任务提交到队列中执行，返回之后就不能取消
常用来在在主队列上延迟执行一项任务
NSLog(@"当前线程 %@", [NSThread currentThread]);
//GCD延时调用(主线程)(主队列)
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
NSLog(@"GCD延时(主线程) %@", [NSThread currentThread]);
});
//GCD延时调用(其他线程)(全局并发队列)
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSLog(@"GCD延时(其他线程) %@", [NSThread currentThread]);
});
//输出: 当前线程 <NSThread: 0x7f8cb9701990>{number = 1, name = main}
//输出: GCD延时(主线程) <NSThread: 0x7f8cb9701990>{number = 1, name = main}
//输出: GCD延时(其他线程) <NSThread: 0x7f8cb9513ee0>{number = 3, name = (null)}
一次性执行 dispatch_once()
整个程序运行中,只会执行一次 (默认线程是安全的)
dispatch_once() 以线程安全的方式执行且仅执行其代码块一次
for (NSInteger i = 0; i < 10; i++) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSLog(@"GCD一次性执行(默认线程是安全的)");
});
}
//输出: GCD一次性执行(默认线程是安全的)
//使用GCD初始化单例
+ (instancetype)sharedManager {
static PhotoManager *sharedPhotoManager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedPhotoManager = [[PhotoManager alloc] init];
});
return sharedPhotoManager;
}
提交 dispatch_apply()
把一项任务提交到队列中多次执行，具体是并行执行还是串行执行由队列本身决定
dispatch_apply不会立刻返回，在执行完毕后才会返回，是同步的调用。
队列
任务1,任务2依次执行,所有任务都执行成功后回到主线程
(效率不高)
NSLog(@"当前线程 %@", [NSThread currentThread]);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//全局并发队列
for (NSInteger i = 0; i < 5; i++) {
NSLog(@"任务1 %@", [NSThread currentThread]);
}
for (NSInteger i = 0; i < 5; i++) {
NSLog(@"任务2 %@", [NSThread currentThread]);
}
dispatch_async(dispatch_get_main_queue(), ^{
//主队列
NSLog(@"主线程执行(刷新UI) %@", [NSThread currentThread]);
});
});
//输出: 当前线程 <NSThread: 0x7fa78040b8b0>{number = 1, name = main}
//输出: 任务1 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务1 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务1 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务1 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务1 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7f9da1416a00>{number = 3, name = (null)}
//输出: 主线程(刷新UI) <NSThread: 0x7f9da1705940>{number = 1, name = main}
队列组
任务1,任务2同时执行,所有任务都执行成功后回到主线程
(效率高)
NSLog(@"当前线程 %@", [NSThread currentThread]);
//(1)创建一个队列组
dispatch_group_t group= dispatch_group_create();
//(2)开启任务1
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
for (NSInteger i = 0; i < 5; i++) {
NSLog(@"任务1 %@", [NSThread currentThread]);
}
});
//(3)开启任务2
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
for (NSInteger i = 0; i < 5; i++) {
NSLog(@"任务2 %@", [NSThread currentThread]);
}
});
//(4)所有任务执行完毕,回到主线程
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"主线程(刷新UI) %@", [NSThread currentThread]);
});
//输出: 当前线程 <NSThread: 0x7fd951704e70>{number = 1, name = main}
//输出: 任务1 <NSThread: 0x7ff65a50b4d0>{number = 3, name = (null)}
//输出: 任务1 <NSThread: 0x7ff65a50b4d0>{number = 3, name = (null)}
//输出: 任务1 <NSThread: 0x7ff65a50b4d0>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7ff65a697770>{number = 4, name = (null)}
//输出: 任务2 <NSThread: 0x7ff65a697770>{number = 4, name = (null)}
//输出: 任务1 <NSThread: 0x7ff65a50b4d0>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7ff65a697770>{number = 4, name = (null)}
//输出: 任务1 <NSThread: 0x7ff65a50b4d0>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7ff65a697770>{number = 4, name = (null)}
//输出: 任务2 <NSThread: 0x7ff65a697770>{number = 4, name = (null)}
//输出: 主线程(刷新UI) <NSThread: 0x7ff65a406fb0>{number = 1, name = main}
串行与并发
各个队列的执行效果
串行队列
串行队列
一个任务执行完毕后，再执行下一个任务
主队列是GCD自带的一种特殊的串行队列,放在主队列中的任务,都会放到主线程中执行
//(1)使用dispatch_queue_create函数创建串行队列
//参数1: 队列名称
//参数2: 队列属性 (一般用NULL)
dispatch_queue_t serialQueue = dispatch_queue_create("serialQueue", NULL);
//(2)使用主队列（跟主线程相关联的队列）
dispatch_queue_t serialMainQueue = dispatch_get_main_queue();
并发队列
并发队列
多个任务并发执行（自动开启多个线程同时执行任务）
<u>并发功能只有在异步（dispatch_async）函数下才有效!!!</u>
GCD默认已经提供了全局的并发队列，供整个应用使用，不需要手动创建
| 并发队列优先级 | 快捷值 | 优先级 |
|---|---|---|
| DISPATCH_QUEUE_PRIORITY_HIGH | 2 | 高 |
| DISPATCH_QUEUE_PRIORITY_DEFAULT | 0 | 中(默认) |
| DISPATCH_QUEUE_PRIORITY_LOW | (-2) | 低 |
| DISPATCH_QUEUE_PRIORITY_BACKGROUND | INT16_MIN | 后台 |
//(1)使用dispatch_get_global_queue函数获得全局的并发队列
//参数1: 优先级
//参数2: 暂时无用参数 (传0)
dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
异步函数_并发队列
(开启新线程,并发执行任务)
NSLog(@"当前线程 %@", [NSThread currentThread]);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSLog(@"任务1 %@", [NSThread currentThread]);
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSLog(@"任务2 %@", [NSThread currentThread]);
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSLog(@"任务3 %@", [NSThread currentThread]);
});
//输出: 当前线程 <NSThread: 0x7fbe83c067c0>{number = 1, name = main}
//输出: 任务1 <NSThread: 0x7fb84160ed90>{number = 3, name = (null)}
//输出: 任务3 <NSThread: 0x7fb841752940>{number = 4, name = (null)}
//输出: 任务2 <NSThread: 0x7fb8414167b0>{number = 5, name = (null)}
异步函数_串行队列
(开启新线程,串行执行任务)
NSLog(@"当前线程 %@", [NSThread currentThread]);
//创建串行队列
dispatch_queue_t serialQueue = dispatch_queue_create("serialQueue", NULL);
dispatch_async(serialQueue, ^{
NSLog(@"任务1 %@", [NSThread currentThread]);
});
dispatch_async(serialQueue, ^{
NSLog(@"任务2 %@", [NSThread currentThread]);
});
dispatch_async(serialQueue, ^{
NSLog(@"任务3 %@", [NSThread currentThread]);
});
//输出: 当前线程 <NSThread: 0x7fc192e05380>{number = 1, name = main}
//输出: 任务1 <NSThread: 0x7fc192c16670>{number = 3, name = (null)}
//输出: 任务2 <NSThread: 0x7fc192c16670>{number = 3, name = (null)}
//输出: 任务3 <NSThread: 0x7fc192c16670>{number = 3, name = (null)}
同步函数_并发队列
(不会开启新线程,并发执行任务失效!)
NSLog(@"当前线程 %@", [NSThread currentThread]);
dispatch_sync(dispatch_get_global_queue(0, 0), ^{
NSLog(@"任务1 %@", [NSThread currentThread]);
});
dispatch_sync(dispatch_get_global_queue(0, 0), ^{
NSLog(@"任务2 %@", [NSThread currentThread]);
});
dispatch_sync(dispatch_get_global_queue(0, 0), ^{
NSLog(@"任务3 %@", [NSThread currentThread]);
});
//输出: 当前线程 <NSThread: 0x7fa0dbf02e20>{number = 1, name = main}
//输出: 任务1 <NSThread: 0x7fa0dbf02e20>{number = 1, name = main}
//输出: 任务2 <NSThread: 0x7fa0dbf02e20>{number = 1, name = main}
//输出: 任务3 <NSThread: 0x7fa0dbf02e20>{number = 1, name = main}
同步函数_串行队列
(不会开启新线程,串行执行任务)
NSLog(@"当前线程 %@", [NSThread currentThread]);
//创建串行队列
dispatch_queue_t serialQueue = dispatch_queue_create("serialQueue", NULL);
dispatch_sync(serialQueue, ^{
NSLog(@"任务1 %@", [NSThread currentThread]);
});
dispatch_sync(serialQueue, ^{
NSLog(@"任务2 %@", [NSThread currentThread]);
});
dispatch_sync(serialQueue, ^{
NSLog(@"任务3 %@", [NSThread currentThread]);
});
//输出: 当前线程 <NSThread: 0x7f8c0b407f00>{number = 1, name = main}
//输出: 任务1 <NSThread: 0x7f8c0b407f00>{number = 1, name = main}
//输出: 任务2 <NSThread: 0x7f8c0b407f00>{number = 1, name = main}
//输出: 任务3 <NSThread: 0x7f8c0b407f00>{number = 1, name = main}
多个网络请求示例
- (void)exampleMoreNetwork{
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t serialQueue = dispatch_queue_create("magic_gcd_group", DISPATCH_QUEUE_SERIAL);
// 网络请求1
dispatch_group_enter(group);
dispatch_group_async(group, serialQueue, ^{
[[MagicNetworkManager shareManager] GET:@"网络请求1" Parameters:nil Success:^(NSURLResponse *response, id responseObject) {
dispatch_group_leave(group);
} Failure:^(NSURLResponse *response, id error) {
dispatch_group_leave(group);
}];
});
// 网络请求2
dispatch_group_enter(group);
dispatch_group_async(group, serialQueue, ^{
[[MagicNetworkManager shareManager] GET:@"网络请求2" Parameters:nil Success:^(NSURLResponse *response, id responseObject) {
dispatch_group_leave(group);
} Failure:^(NSURLResponse *response, id error) {
dispatch_group_leave(group);
}];
});
// 所有网络请求结束
dispatch_group_notify(group, serialQueue, ^{
dispatch_async(dispatch_get_global_queue(0, 0), ^{
dispatch_async(dispatch_get_main_queue(), ^{
// 主线程刷新UI
});
});
});
}
多张图片上传示例
- (void)networkUploadWithURLString:(NSString *)URLString images:(NSMutableArray *)images {
NSMutableArray *result = [NSMutableArray array];
for (NSInteger i = 0; i < images.count; i++) {
[result addObject:[NSNull null]];
}
dispatch_group_t group = dispatch_group_create();
for (NSInteger i = 0; i < images.count; i++) {
dispatch_group_enter(group);
//1. 图片存放地址
NSString *url = URLString;
//2. 图片名称自定义
NSString *imageName = [[NSDate date] formattedDateWithFormat:@"yyyyMMddHHmmss"];
NSString *fileName = [NSString stringWithFormat:@"%@_%ld.png",imageName,i];
//3. 图片二进制文件
NSData *imageData = UIImagePNGRepresentation(images[i]);
//NSLog(@"文件大小: %ld k", (long)(imageData.length / 1024));
//4. 发起网络请求
AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
manager.requestSerializer = [AFJSONRequestSerializer serializer];
manager.responseSerializer = [AFJSONResponseSerializer serializer];
manager.responseSerializer.acceptableContentTypes = [NSSet setWithObjects:@"text/plain", @"application/json", @"text/html", nil];
[manager POST:url parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> _Nonnull formData) {
[formData appendPartWithFileData:imageData name:@"file" fileName:fileName mimeType:@"image/png"];
} progress:^(NSProgress * _Nonnull uploadProgress) {
} success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"第 %d 张图片上传成功: %@", (int)i + 1, responseObject);
// NSMutableArray 是线程不安全的，所以加个同步锁
@synchronized (result) {
result[i] = responseObject;
}
dispatch_group_leave(group);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"第 %d 张图片上传失败: %@", (int)i + 1, error);
dispatch_group_leave(group);
}];
}
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"上传完成!");
for (id response in result) {
NSLog(@"%@", response);
}
});
}
