GCD中的一些高级特性

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@interface DataManager ()

@property (strong, nonatomic) NSMutableArray *dataArray;
@property (strong, nonatomic) dispatch_queue_t concurrentDataQueue;

@end

@implementation DataManager

+ (instancetype)shareInstance {
static DataManager *dataManager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
dataManager = [[DataManager alloc] init];
dataManager.concurrentDataQueue = dispatch_queue_create("com.kingiol.gcd.dataManagerQueue", DISPATCH_QUEUE_CONCURRENT);
});
return dataManager;
}

- (NSArray *)data {
__block NSArray *returnData = nil;
dispatch_sync(self.concurrentDataQueue, ^{
returnData = [_dataArray copy];
});
return returnData;
}

- (void)addData:(id)data {
if (data) {
dispatch_barrier_async(self.concurrentDataQueue, ^{
[_dataArray addObject:data];
});
}
}

@end

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dispatch_group_t downloadGroup = dispatch_group_create();
for (NSInteger i = 0; i < 3; i++) {
dispatch_group_enter(downloadGroup);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//下载图片程序
//在图片下载完成的block中调用:
dispatch_group_leave(downloadGroup);
});
}
dispatch_group_notify(downloadGroup, dispatch_get_main_queue(), ^{
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:nil message:@"全部下载完成" delegate:nil cancelButtonTitle:@"cancel" otherButtonTitles:nil, nil];
[alertView show];
});