@implementation TestObj

-(void)method1{
  NSLog(@"Method1");
}
-(void)method2{
  NSLog(@"Method2");
}

@end

NSLock *lock = [[NSLock alloc] init];
//线程1
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    [lock lock];
    [obj method1];
    sleep(10);
    [lock unlock];
});
//线程2
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    sleep(1);//以保证让线程2的代码后执行
    [lock lock];
    [obj method2];
    [lock unlock];
});

//主线程中
TestObj *obj = [[TestObj alloc] init];
//线程1
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    @synchronized(obj){
        [obj method1];
        sleep(10);
    }
});
//线程2
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    sleep(1);
    @synchronized(obj){
        [obj method2];
    }
});

//主线程中
TestObj *obj = [[TestObj alloc] init];
__block pthread_mutex_t mutex;
pthread_mutex_init(&mutex, NULL);
//线程1
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    pthread_mutex_lock(&mutex);
    [obj method1];
    sleep(5);
    pthread_mutex_unlock(&mutex);
});
//线程2
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    sleep(1);
    pthread_mutex_lock(&mutex);
    [obj method2];
    pthread_mutex_unlock(&mutex);
});

//主线程中
TestObj *obj = [[TestObj alloc] init];
dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);
//线程1
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    [obj method1];
    sleep(10);
    dispatch_semaphore_signal(semaphore);
});
//线程2
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    sleep(1);
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    [obj method2];
    dispatch_semaphore_signal(semaphore);
});

+ (UIImage *)circularScaleAndCropImage:(UIImage *)image {
  // Create the bitmap graphics context
  UIGraphicsBeginImageContextWithOptions(CGSizeMake(image.size.width, image.size.height), NO, 0.0);
  CGContextRef context = UIGraphicsGetCurrentContext();

  // Get the width and heights
  CGFloat imageWidth = image.size.width;
  CGFloat imageHeight = image.size.height;

  // Calculate the centre of the circle
  CGFloat imageCentreX = imageWidth / 2;
  CGFloat imageCentreY = imageHeight / 2;

  // Create and CLIP to a CIRCULAR Path
  CGFloat radius = imageWidth / 2;
  CGContextBeginPath(context);
  CGContextAddArc(context, imageCentreX, imageCentreY, radius, 0, 2 * M_PI, 0);
  CGContextClosePath(context);
  CGContextClip(context);

  // Draw the IMAGE
  CGRect myRect = CGRectMake(0, 0, imageWidth, imageHeight);
  [image drawInRect:myRect];

  UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();

  return newImage;
}