iOS-多线程
一 多线程之间的关系
2、
二 NSThread
一旦线程停止死亡了，就不能再启动。所以线程NSThread不能为全局变量
1>.创建和启动
1.第一种方法：直接创建，手动启动
NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(download：) object:@"www.baidu.com"];
[thread start];
2.第二种方法：创建后立即启动
[NSThread detachNewThreadSelector:@selector(download) toTarget:self withObject:@"www.baidu.com"];
3.第三种方法：隐式创建
//主线程
[self performSelector:@selector(download:) withObject:@"www.baidu.com"];
//子线程
[self performSelectorInBackground:@selector(download:) withObject:@"www.baidu.com"];
object是selector方法传递的参数
-(void)download:(NSString *)url
{
NSLog(@"download-- %@ %@",url,[NSThread currentThread]);
}
2>.睡眠的用法
延迟执行不要勇sleep，坏处：卡住主线程 1.第一种 [NSThread sleepForTimeInterval:5.0]; 2.第二种 NSDate *date = [NSDate dateWithTimeIntervalSinceNow:3.0]; [NSThread sleepUntilDate:date];
3>.强制停止进程
+(void)exit
4>.其他用法
+(NSThread *)mainThread； +(NSThread *)currentThread -(BOOL)isMainThread; +(BOOL)isMainThread;
5>.线程间通信
在1个进程中，线程往往不是孤立存在的，多个线程之间需要经常进行通信。体现在两个方面：一，1个线程的数据传递给另一个线程。二，在1个线程中执行完特定任务后，转到另一个线程继续执行任务
-(void)download:(NSString *)url
{
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:url]];
UIImage *image = [UIImage imageWithData:data];
[self performSelectorOnMainThread:@selector(pic:) withObject:image waitUntilDone:YES];
}
-(void)pic:(UIImage *)image
{
NSLog(@"pic:%@",image);
self.imageView.image = image;
}
-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
[self performSelector:@selector(download:) withObject:@"http://g.hiphotos.baidu.com/image/h%3D200/sign=f23ec3ed1fd8bc3ed90801cab289a6c8/7a899e510fb30f24dc189ad4ce95d143ac4b0362.jpg"];
}
三 GCD
1>线程：同步与异步
同步：只能在当前线程中执行任务，不具备开启新线程的能力
异步：可以在新的线程中执行任务，具备开启新线程的能力
2>任务：并发与串行
并发：可以让多个任务并发（同时）执行，自动开启多线程。只有在异步下才有效
串行：让任务一个接一个地执行
-(void)asyncGlobalQueue
{
//获得全局的并发队列
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); //第一个参数是优先级
//异步并行。自动创建多条线程
dispatch_async(queue, ^{
NSLog(@"将任务放到全局队列中执行 %@", [NSThread currentThread]);
dispatch_async(queue, ^{
NSLog(@"异步并行1 %@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"异步并行2 %@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"异步并行3 %@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"异步并行4 %@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"异步并行5 %@", [NSThread currentThread]);
});
});
}
-(void)asyncSerialQueue
{
//异步串行，自动会创建线程，但只开1条
dispatch_queue_t queue = dispatch_queue_create("cn.wx", NULL);
dispatch_async(queue, ^{
NSLog(@"异步串行1 %@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"异步串行2 %@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"异步串行3 %@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"异步串行4 %@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"异步串行5 %@", [NSThread currentThread]);
});
}
-(void)syncGlobalQueue
{
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//同步并行。不会创建线程，使用主线程
dispatch_sync(queue, ^{
NSLog(@"同步并行1 %@", [NSThread currentThread]);
NSLog(@"同步并行2 %@", [NSThread currentThread]);
NSLog(@"同步并行3 %@", [NSThread currentThread]);
NSLog(@"同步并行4 %@", [NSThread currentThread]);
NSLog(@"同步并行5 %@", [NSThread currentThread]);
});
}
-(void)syncSerialQueue
{
dispatch_queue_t queue = dispatch_queue_create("cn.wx", NULL);
//同步串行。不会创建线程，使用主线程
dispatch_sync(queue, ^{
NSLog(@"同步并行1 %@", [NSThread currentThread]);
NSLog(@"同步并行2 %@", [NSThread currentThread]);
NSLog(@"同步并行3 %@", [NSThread currentThread]);
NSLog(@"同步并行4 %@", [NSThread currentThread]);
NSLog(@"同步并行5 %@", [NSThread currentThread]);
});
}
3>.主队列
-(void)mainQueue
{
dispatch_queue_t queue = dispatch_get_main_queue();
dispatch_async(queue, ^{
NSLog(@"虽然是异步，但是是在主线程执行，所以不会开线程");
});
// dispatch_sync(queue, ^{
// NSLog(@"不能在串行上使用主队列，否则会阻塞");
// });
}
4>.线程间通信
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
NSLog(@"子线程进行操作");
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"回主线程加载图片");
});
});
5>.延时执行
不要使用sleep，会卡住主线程
第一种：
[self performSelector:@selector(down) withObject:@"abv" afterDelay:3];
第二种：
dispatch_queue_t queue = dispatch_get_main_queue();
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), queue, ^{
NSLog(@"xx");//回到主线程
});
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), queue, ^{
NSLog(@"xx");//回到子线程
});
6>.只执行一次
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSLog(@"xx");
})
四 NSOperation
1>.简述
先将需要执行的操作封装到一个NSOperation对象，一个对象就相当于GCD的一个block
然后将NSOperation对象添加到NSOperationQueue中
系统会自动将NSOperationQueue中的NSOperation取出来
将取出的NSOperation封装的操作放到一条线程中执行
2>.NSOperation的使用
NSOperation是个抽象类，不具备封装的能力，必须使用它的子类
1>NSInvocationOperation
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(download) object:nil]; /* [operation start]; 如果直接start，那么将会在当前线程（主线程）同步执行 */ //添加操作到队列中 [queue addOperation:operation];
2>NSBlockOperation
第一种情况：同步
NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"下载一 %@",[NSThread currentThread]);
}];
[operation start]; // 如果直接start，那么将会在当前线程（主线程）同步执行
第二种情况：异步
NSBlockOperation *operation = [[NSBlockOperation alloc] init];
//operation操作添加多个操作
[operation addExecutionBlock:^{
NSLog(@"下载一 %@",[NSThread currentThread]);
}];
[operation addExecutionBlock:^{
NSLog(@"下载二 %@",[NSThread currentThread]);
}];
[operation addExecutionBlock:^{
NSLog(@"下载三 %@",[NSThread currentThread]);
}];
[operation start];
ps：NSBlockOperation还可以直接创建使用对象
NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"下载一 %@",[NSThread currentThread]);
}];
3>自定义子类继承NSOperation
3.NSOperationQueue的使用
1>.基本使用
//1.创建一个队列（非主队列）
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
//设置最大并发数
queue.maxConcurrentOperationCount = 2;
//2.创建操作
NSBlockOperation *operation1 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"下载图片1 -- %@",[NSThread currentThread]);
}];
NSBlockOperation *operation2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"下载图片2 -- %@",[NSThread currentThread]);
}];
NSInvocationOperation *operation3 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(down) object:nil];
//操作完后马上执行另一个操作
[operation1 setCompletionBlock:^{
NSLog(@"下载图片222");
}];
//操作依赖,注意不能相互依赖
[operation2 addDependency:operation1];
[operation3 addDependency:operation2];
//3.添加操作到队列中（自动异步执行任务，并发）
[queue addOperation:operation1];
[queue addOperation:operation2];
[queue addOperation:operation3];
2>其他用法
[queue cancelAllOperations]; //取消队列的所有操作。也可以直接调用NSOperation的cancel
[queue setSuspended:YES]; //暂停和恢复队列。yes为暂停
常用场景：
-(void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
[queue cancelAllOperations];
}
-(void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView
{
[queue setSuspended:YES];
}
-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
[queue setSuspended:NO];
}
3>.线程安全
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperationWithBlock:^{
//1.异步下载图片
NSURL *url = [NSURL URLWithString:@"www.baidu.com"];
NSData *data = [NSData dataWithContentsOfURL:url];
UIImage *image = [UIImage imageWithData:data];
//2.回到主线程设置图片
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
self.imageView.image = image;
}];
}];
五 互斥锁
self.obj = [[NSObject alloc] init];
//锁任意对象，并且需要是唯一一把，所以需要建立个全局变量对象
@synchronized(self.obj) {
}
2.atomic:线程安全，需要消耗大量的资源。不建议需要
六 线程注意点
1.不要同时开太多线材（1~3条线材即可，不要超过5条）
2.线程概念
1>主线程：UI线程，显示、刷新UI界面，处理UI控件的事件
2>子线程：后台线程，异步线程
3.不要把耗时的操作放在主线程，要放在子线程中执行