多线程之NSOperation
套话
与GCD一样，NSOperation也是我们日常开发中经常用到的多线程技术。本文将会介绍NSOperation的基本使用、添加依赖、
初次使用
NSOperation是个抽象类，依赖于子类NSInvocationOperation、NSBlockOperation去实现
下面是开发者文档上对NSOperation的一段描述
NSInvocationOperation
基本使用
- (void)test {
// 处理事务
NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(handleInvocation:) object:@"Felix"];
// 创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
// 操作加入队列
[queue addOperation:op];
}
- (void)handleInvocation:(id)operation {
NSLog(@"%@ --- %@",operation, [NSThread currentThread]);
}
--------------------输出结果：-------------------
Felix --- <NSThread: 0x6000000422c0>{number = 3, name = (null)}
--------------------输出结果：-------------------
直接处理事务，不添加隐性队列
- (void)test {
NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(handleInvocation:) object:@"Felix"];
[op start];
}
- (void)test {
NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(handleInvocation:) object:@"Felix"];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperation:op];
[op start];
}
上述代码之所以会崩溃，是因为线程生命周期：
queue addOperation:op已经将处理事务的操作任务加入到队列中，并让线程运行op start将已经运行的线程再次运行会造成线程混乱
NSBlockOperation
NSInvocationOperation和NSBlockOperation两者的区别在于：
- 前者类似
target形式 - 后者类似
block形式——函数式编程，业务逻辑代码可读性更高
- (void)test {
// 初始化添加事务
NSBlockOperation *bo = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"任务1————%@",[NSThread currentThread]);
}];
// 添加事务
[bo addExecutionBlock:^{
NSLog(@"任务2————%@",[NSThread currentThread]);
}];
// 回调监听
bo.completionBlock = ^{
NSLog(@"完成了!!!");
};
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperation:bo];
NSLog(@"事务添加进了NSOperationQueue");
}
--------------------输出结果：-------------------
事务添加进了NSOperationQueue
任务1————<NSThread: 0x6000032dc1c0>{number = 5, name = (null)}
任务2————<NSThread: 0x6000032a1880>{number = 4, name = (null)}
完成了!!!
--------------------输出结果：-------------------
NSOperationQueue是异步执行的，所以任务一、任务二的完成顺序不确定
执行顺序
下列代码可以证明操作与队列的执行效果是异步并发的
- (void)test {
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
for (int i = 0; i < 5; i++) {
[queue addOperationWithBlock:^{
NSLog(@"%@---%d", [NSThread currentThread], i);
}];
}
}
--------------------输出结果：-------------------
<NSThread: 0x600002771600>{number = 3, name = (null)}---0
<NSThread: 0x60000277ac80>{number = 7, name = (null)}---3
<NSThread: 0x600002774840>{number = 6, name = (null)}---2
<NSThread: 0x600002776a80>{number = 8, name = (null)}---4
<NSThread: 0x60000270c540>{number = 5, name = (null)}---1
--------------------输出结果：-------------------
设置优先级
NSOperation设置优先级只会让CPU有更高的几率调用，不是说设置高就一定全部先完成
- 不使用
sleep——高优先级的任务一先于低优先级的任务二
- (void)test {
NSBlockOperation *bo1 = [NSBlockOperation blockOperationWithBlock:^{
for (int i = 0; i < 5; i++) {
//sleep(1);
NSLog(@"第一个操作 %d --- %@", i, [NSThread currentThread]);
}
}];
// 设置最高优先级
bo1.qualityOfService = NSQualityOfServiceUserInteractive;
NSBlockOperation *bo2 = [NSBlockOperation blockOperationWithBlock:^{
for (int i = 0; i < 5; i++) {
NSLog(@"第二个操作 %d --- %@", i, [NSThread currentThread]);
}
}];
// 设置最低优先级
bo2.qualityOfService = NSQualityOfServiceBackground;
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperation:bo1];
[queue addOperation:bo2];
}
--------------------输出结果：-------------------
第一个操作 0 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第一个操作 1 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第一个操作 2 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第一个操作 3 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第一个操作 4 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第二个操作 0 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
第二个操作 1 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
第二个操作 2 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
第二个操作 3 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
第二个操作 4 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
--------------------输出结果：-------------------
- 使用
sleep进行延时——高优先级的任务一慢于低优先级的任务二
第二个操作 0 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第二个操作 1 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第二个操作 2 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第二个操作 3 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第二个操作 4 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第一个操作 0 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}
第一个操作 1 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}
第一个操作 2 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}
第一个操作 3 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}
第一个操作 4 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}
线程间通讯
- 在
GCD中使用异步进行网络请求，然后回到主线程刷新UI NSOperation中也有类似在线程间通讯的操作
- (void)test {
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.name = @"Felix";
[queue addOperationWithBlock:^{
NSLog(@"请求网络%@--%@", [NSOperationQueue currentQueue], [NSThread currentThread]);
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
NSLog(@"刷新UI%@--%@", [NSOperationQueue currentQueue], [NSThread currentThread]);
}];
}];
}
--------------------输出结果：-------------------
请求网络<NSOperationQueue: 0x7ff4a240bae0>{name = 'Felix'}--<NSThread: 0x6000007dcf00>{number = 5, name = (null)}
刷新UI<NSOperationQueue: 0x7ff4a24087d0>{name = 'NSOperationQueue Main Queue'}--<NSThread: 0x60000078c8c0>{number = 1, name = main}
--------------------输出结果：-------------------
设置并发数
- 在
GCD中只能使用信号量来设置并发数 - 而
NSOperation轻易就能设置并发数 -
- 通过
设置maxConcurrentOperationCount来控制单次出队列去执行的任务数
- 通过
- (void)test {
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.name = @"Felix";
queue.maxConcurrentOperationCount = 2;
for (int i = 0; i < 5; i++) {
[queue addOperationWithBlock:^{ // 一个任务
[NSThread sleepForTimeInterval:2];
NSLog(@"%d-%@",i,[NSThread currentThread]);
}];
}
}
--------------------输出结果：-------------------
1-<NSThread: 0x6000009290c0>{number = 5, name = (null)}
0-<NSThread: 0x6000009348c0>{number = 8, name = (null)}
3-<NSThread: 0x6000009290c0>{number = 5, name = (null)}
2-<NSThread: 0x60000094b0c0>{number = 7, name = (null)}
4-<NSThread: 0x6000009348c0>{number = 8, name = (null)}
--------------------输出结果：-------------------
添加依赖
在NSOperation中添加依赖能很好的控制任务执行的先后顺序
- (void)test {
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
NSBlockOperation *bo1 = [NSBlockOperation blockOperationWithBlock:^{
[NSThread sleepForTimeInterval:0.5];
NSLog(@"请求token");
}];
NSBlockOperation *bo2 = [NSBlockOperation blockOperationWithBlock:^{
[NSThread sleepForTimeInterval:0.5];
NSLog(@"拿着token,请求数据1");
}];
NSBlockOperation *bo3 = [NSBlockOperation blockOperationWithBlock:^{
[NSThread sleepForTimeInterval:0.5];
NSLog(@"拿着数据1,请求数据2");
}];
//添加依赖
[bo2 addDependency:bo1];
[bo3 addDependency:bo2];
[queue addOperations:@[bo1,bo2,bo3] waitUntilFinished:YES];
NSLog(@"执行完了?我要干其他事");
}
--------------------输出结果：-------------------
请求token
拿着token,请求数据1
拿着数据1,请求数据2
执行完了?我要干其他事
--------------------输出结果：-------------------
注意不要添加依赖导致循环运用，会导致依赖无效并会在控制台打印出"XPC connection interrupted"
任务的挂起、继续、取消
// 挂起
queue.suspended = YES;
// 继续
queue.suspended = NO;
// 取消
[queue cancelAllOperations];
这幅图是并发量为2的情况：
- 挂起前：任务3、任务4等待被调度
- 挂起瞬间：任务3、任务4已经被调度出队列，准备执行，此时它们是无法挂起的
- 挂起后：任务3、任务4被线程执行，而原来的队列被挂起不能被调度
自定义NSOperation缓存机制
NSOperation异步处理
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
UIImageView *imageView = [[UIImageView alloc] init];
imageView.frame = CGRectMake(100, 100, 100, 100);
[self.view addSubview:imageView];
NSString *urlStr = [NSString stringWithFormat:@"https://profile-avatar.csdnimg.cn/910a183044d54231b5e418c23a558516_weixin_61196797.jpg!1"];
NSURL *imageURL = [NSURL URLWithString:urlStr];
NSBlockOperation *bo = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"去下载图片" );
// 延迟
NSData *data = [NSData dataWithContentsOfURL:imageURL];
UIImage *image = [UIImage imageWithData:data];
// 更新UI
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
imageView.image = image;
NSLog(@"加载完成");
imageView.backgroundColor = [UIColor redColor];
}];
}];
[queue addOperation:bo];
