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. //Resize if neccessary to ensure it's not pixelated
7. if (_image.size.height <= self.photoImageView.bounds.size.height &&
8. _image.size.width <= self.photoImageView.bounds.size.width) {
9. [self.photoImageView setContentMode:UIViewContentModeCenter];
10. }
11. dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ // 1
12. UIImage *overlayImage = [self faceOverlayImageFromImage:_image];
13. dispatch_async(dispatch_get_main_queue(), ^{ // 2
14. [self fadeInNewImage:overlayImage]; // 3
15. });
16. });
17. }

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. dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
5. [PhotoManager sharedManager];
6. });

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. // ADD THIS:
9. sharedPhotoManager->_concurrentPhotoQueue = dispatch_queue_create("com.selander.GooglyPuff.photoQueue",
10. DISPATCH_QUEUE_CONCURRENT);
11. });
12. return sharedPhotoManager;
13. }

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

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

CocoaChina是全球最大的苹果开发中文社区，官方微信每日定时推送各种精彩的 研发教程资源和工具，介绍app推广营销经验，最新企业招聘和外包信息，以及Cocos2d引擎、Cocos Studio开发工具包的最新动态及培训信息。关注微信可以第一时间了解最新产品和服务动态，微信在手，天下我有！