iOS之多线程精髓

NSThread*thread = [[NSThread alloc] initWithTarget:self selector:@selector(run)object:nil];

[thread start];

+ (NSThread *)mainThread;//获得主线程

- (BOOL)isMainThread;//是否为主线程

+ (BOOL)isMainThread;//是否为主线程

- (void)setName:(NSString *)n;

- (NSString*)name;

[NSThread detachNewThreadSelector:@selector(run)toTarget:self withObject:nil];

[self performSelectorInBackground:@selector(run)withObject:nil];

- (void)start;

//进入就绪状态 ->运行状态。当线程任务执行完毕，自动进入死亡状态

+ (void)sleepUntilDate:(NSDate*)date;

+ (void)sleepForTimeInterval:(NSTimeInterval)ti;

//进入阻塞状态

+ (void)exit;

//进入死亡状态

注意：一旦线程停止（死亡）了，就不能再次开启任务

@synchronized(锁对象) { //需要锁定的代码  }

注意：锁定1份代码只用1把锁，用多把锁是无效的

 优点:

    <1> GCD 能够自动利用更多的CPU的核数(双核/四核)!

    <2> GCD 会自动管理线程的生命周期.

  1> dispatch_async + 全局并发队列 (可以开启多条线程)

   2> dispatch_async + 自己创建的串行队列 (开启一条线程)

dispatch_sync(dispatch_queue_tqueue, dispatch_block_tblock);

dispatch_async(dispatch_queue_tqueue, dispatch_block_tblock);

dispatch_async(

dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

   //执行耗时的异步操作...

     dispatch_async(dispatch_get_main_queue(),^{

        //回到主线程，执行UI刷新操作

        });

});

[self performSelector:@selector(run)withObject:nil afterDelay:2.0];

// 2秒后再调用self的run方法

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(),^{

   //2秒后执行这里的代码...在哪个线程执行，跟队列类型有关

});

static dispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

   //只执行1次的代码(这里面默认是线程安全的)

});

ARC

+ (instancetype)sharedMusicTool {

   if (_instance == nil) { //防止频繁加锁

          @synchronized(self) {

            if (_instance == nil) { //防止创建多次

               _instance = [[self alloc] init];

            }

        }

   }

   return _instance;

}

- (id)copyWithZone:(struct _NSZone*)zone {

   return _instance;

}

- (id)retain { return self; }

- (NSUInteger)retainCount { return 1; }

- (oneway void)release{}

- (id)autorelease { return self; }

.单例实现:(两种方式:互斥锁(@synchronized(self))和一次性代码(dispatch_once));

//(1)重写 allocWithZone:方法,在这里创建唯一的实例(注意线程安全). //alloc 内部都会调用这个方法.

        +(instancetype)allocWithZone:(struct_NSZone *)zone {

           if(_instance ==nil) { // 防止频繁加锁

               @synchronized(self) {

                   if(_instance ==nil) { // 防止创建多次

                        _instance = [superallocWithZone:zone];

                    }

                }

            }

           return_instance;

        }

   //(2)重写 copyWithZone:方法.

        +(id)copyWithZone:(struct_NSZone *)zone

        {

           return_instance;

        }

- (id)initWithTarget:(id)targetselector:(SEL)selobject:(id)arg;

- (void)start;

+ (id)blockOperationWithBlock:(void (^)(void))block;

- (void)addExecutionBlock:(void (^)(void))block;

- (void)addOperation:(NSOperation*)op;

- (NSInteger)maxConcurrentOperationCount;

- (void)setMaxConcurrentOperationCount:(NSInteger)cnt;

- (void)cancelAllOperations;

提示：也可以调用NSOperation的- (void)cancel方法取消单个操作

- (void)setSuspended:(BOOL)b; //YES代表暂停队列，NO代表恢复队列

- (BOOL)isSuspended;

- (NSOperationQueuePriority)queuePriority;

- (void)setQueuePriority:(NSOperationQueuePriority)p;

- (void (^)(void))completionBlock;

- (void)setCompletionBlock:(void (^)(void))block;