GCD 深入理解（一）

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http://www.cocoachina.com/industry/20140428/8248.html

本文由@nixzhu翻译至raywenderlich的《grand-central-dispatch-in-depth-part-1》

1. - (void)viewDidLoad 
2. {    
3.     [super viewDidLoad]; 
4.     NSAssert(_image, @"Image not set; required to use view controller"); 
5.     self.photoImageView.image = _image; 
6.  
7.     //Resize if neccessary to ensure it‘s not pixelated 
8.     if (_image.size.height <= self.photoImageView.bounds.size.height && 
9.         _image.size.width <= self.photoImageView.bounds.size.width) { 
10.         [self.photoImageView setContentMode:UIViewContentModeCenter]; 
11.     } 
12.  
13.     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ // 1 
14.         UIImage *overlayImage = [self faceOverlayImageFromImage:_image]; 
15.         dispatch_async(dispatch_get_main_queue(), ^{ // 2 
16.             [self fadeInNewImage:overlayImage]; // 3 
17.         }); 
18.     }); 
19. } 

1. - (void)showOrHideNavPrompt 
2. { 
3.     NSUInteger count = [[PhotoManager sharedManager] photos].count; 
4.     double delayInSeconds = 1.0; 
5.     dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC)); // 1  
6.     dispatch_after(popTime, dispatch_get_main_queue(), ^(void){ // 2  
7.         if (!count) { 
8.             [self.navigationItem setPrompt:@"Add photos with faces to Googlyify them!"]; 
9.         } else { 
10.             [self.navigationItem setPrompt:nil]; 
11.         } 
12.     }); 
13. } 

1. + (instancetype)sharedManager     
2. { 
3.     static PhotoManager *sharedPhotoManager = nil; 
4.     if (!sharedPhotoManager) { 
5.         sharedPhotoManager = [[PhotoManager alloc] init]; 
6.         sharedPhotoManager->_photosArray = [NSMutableArray array]; 
7.     } 
8.     return sharedPhotoManager; 
9. } 

1. + (instancetype)sharedManager   
2. { 
3.     static PhotoManager *sharedPhotoManager = nil; 
4.     if (!sharedPhotoManager) { 
5.         [NSThread sleepForTimeInterval:2]; 
6.         sharedPhotoManager = [[PhotoManager alloc] init]; 
7.         NSLog(@"Singleton has memory address at: %@", sharedPhotoManager); 
8.         [NSThread sleepForTimeInterval:2]; 
9.         sharedPhotoManager->_photosArray = [NSMutableArray array]; 
10.     } 
11.     return sharedPhotoManager; 
12. } 

1. dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ 
2.     [PhotoManager sharedManager]; 
3. }); 
4.  
5. dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ 
6.     [PhotoManager sharedManager]; 
7. }); 

1. + (instancetype)sharedManager 
2. { 
3.     static PhotoManager *sharedPhotoManager = nil; 
4.     static dispatch_once_t onceToken; 
5.     dispatch_once(&onceToken, ^{ 
6.         [NSThread sleepForTimeInterval:2]; 
7.         sharedPhotoManager = [[PhotoManager alloc] init]; 
8.         NSLog(@"Singleton has memory address at: %@", sharedPhotoManager); 
9.         [NSThread sleepForTimeInterval:2]; 
10.         sharedPhotoManager->_photosArray = [NSMutableArray array]; 
11.     }); 
12.     return sharedPhotoManager; 
13. } 

1. + (instancetype)sharedManager 
2. { 
3.     static PhotoManager *sharedPhotoManager = nil; 
4.     static dispatch_once_t onceToken; 
5.     dispatch_once(&onceToken, ^{ 
6.         sharedPhotoManager = [[PhotoManager alloc] init]; 
7.         sharedPhotoManager->_photosArray = [NSMutableArray array]; 
8.     }); 
9.     return sharedPhotoManager; 
10. } 

1. - (void)addPhoto:(Photo *)photo 
2. { 
3.     if (photo) { 
4.         [_photosArray addObject:photo]; 
5.         dispatch_async(dispatch_get_main_queue(), ^{ 
6.             [self postContentAddedNotification]; 
7.         }); 
8.     } 
9. } 

1. - (NSArray *)photos 
2. { 
3.   return [NSArray arrayWithArray:_photosArray]; 
4. } 

1. @interface PhotoManager () 
2. @property (nonatomic,strong,readonly) NSMutableArray *photosArray; 
3. @property (nonatomic, strong) dispatch_queue_t concurrentPhotoQueue; ///< Add this 
4. @end 

1. - (void)addPhoto:(Photo *)photo 
2. { 
3.     if (photo) { // 1 
4.         dispatch_barrier_async(self.concurrentPhotoQueue, ^{ // 2  
5.             [_photosArray addObject:photo]; // 3 
6.             dispatch_async(dispatch_get_main_queue(), ^{ // 4 
7.                 [self postContentAddedNotification];  
8.             }); 
9.         }); 
10.     } 
11. } 

1. - (NSArray *)photos 
2. { 
3.     __block NSArray *array; // 1 
4.     dispatch_sync(self.concurrentPhotoQueue, ^{ // 2 
5.         array = [NSArray arrayWithArray:_photosArray]; // 3 
6.     }); 
7.     return array; 
8. } 

1. + (instancetype)sharedManager 
2. { 
3.     static PhotoManager *sharedPhotoManager = nil; 
4.     static dispatch_once_t onceToken; 
5.     dispatch_once(&onceToken, ^{ 
6.         sharedPhotoManager = [[PhotoManager alloc] init]; 
7.         sharedPhotoManager->_photosArray = [NSMutableArray array]; 
8.  
9.         // ADD THIS: 
10.         sharedPhotoManager->_concurrentPhotoQueue = dispatch_queue_create("com.selander.GooglyPuff.photoQueue", 
11.                                                     DISPATCH_QUEUE_CONCURRENT);  
12.     }); 
13.  
14.     return sharedPhotoManager; 
15. } 

1. - (void)viewDidLoad 
2. { 
3.   [super viewDidLoad]; 
4.  
5.   dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ 
6.  
7.       NSLog(@"First Log"); 
8.  
9.   }); 
10.  
11.   NSLog(@"Second Log"); 
12. } 

 

1. - (void)viewDidLoad 
2. { 
3.   [super viewDidLoad]; 
4.  
5.   dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ 
6.  
7.       NSLog(@"First Log"); 
8.  
9.   }); 
10.  
11.   NSLog(@"Second Log"); 
12. } 

 

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GCD 深入理解（一）

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原文地址：http://www.cnblogs.com/zhoup/p/4514804.html