iOS多线程备忘

进程与线程

进程: 启动Chrome浏览器，就是启动一个进程

线程：使用Chrome一遍下载一遍浏览网页，这个时候有多个线程，下载的线程和加载网页的线程.

一个进程至少有一个线程，线程在进程中执行。线程中串行执行任务，同一时间只能执行一个任务。

NSThread

开启一个线程进行任务处理

[NSThread detachNewThreadSelector:@selector(dosomething) toTarget:self withObject:nil];
[NSThread detachNewThreadWithBlock:^{
        [self dosomething];
    }];
NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(dosomething) object:nil];
    [thread start];

NSObject类拓展直接使用

[self performSelectorInBackground:@selector(dosomething) withObject:nil];
[self performSelectorOnMainThread:@selector(dosomething) withObject:nil waitUntilDone:NO];
[self performSelector:@selector(dosomething) withObject:nil];

创建一个异步任务在后台执行，然后在主线程更新UI操作

[self performSelectorInBackground:@selector(requestData:) withObject:@"https://xxx.png"];


- (void)requestData:(NSString *)urlString
{
    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];
    [self performSelectorOnMainThread:@selector(updateUI:) withObject:data waitUntilDone:NO];
}

- (void)updateUI:(NSData *)data
{
    // 拿到data，跟新UI
}

NSOperation、NSOperationQueue

Grand Centeral Dispatch

并行与串行

dispatch_get_global_queue 全局并行队列
dispatch_get_main_queue 主线程串行队列

dispatch_sync(xxx, ^{ }) 同步线程
dispatch_async(xxx, ^{ }) 异步线程

搭配使用

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        // 子线程中耗时操作
        dispatch_async(dispatch_get_main_queue(), ^{
            // 主线程中更新页面
        });
    });

GCD单例

static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
        
});

执行一次，常用来写单例方法

+ (id)sharedManager {
    
    static dispatch_once_t once;
    
    static id instance;
    
    dispatch_once(&once, ^{
        
        instance = [[self alloc] init];
        
    });
    
    return instance;
    
}

GCD定时器

__block int timeout = 3;
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);
dispatch_source_set_timer(timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); //每秒执行
dispatch_source_set_event_handler(timer, ^{
    if(timeout<=0){ //倒计时结束，关闭
                
        dispatch_async(dispatch_get_main_queue(), ^{
                           
        });
     }else{
        
        dispatch_async(dispatch_get_main_queue(), ^{           
                    
        });
        timeout--;
     }
    });
 dispatch_resume(timer);

dispatch_after延后执行

double delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t) (delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
    // 两秒后执行
});

Dispatch Group

有时候一个页面需要发多个请求，待所以请求完毕，再去更新数据

dispatch_queue_t queue = dispatch_queue_create(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, queue, ^{
    NSLog(@"111");
});

dispatch_group_async(group, queue, ^{
    NSLog(@"222");
});
   
dispatch_group_async(group, queue, ^{
    NSLog(@"333");
});
   
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
    NSLog(@"done");
});
   
/* dispatch_group_notify 也可以换成下面dispatch_group_wait 等待上面执行完毕再往下执行*/
//dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
//NSLog(@"done");