ios GCD的使用及封装

实现代码：

CGDHelper

 /*
  *  Grand Central Dispatch (GCD)是Apple开发的一个多核编程的解决方法。
  *  系统要求：iOS4.0以上。
  */  

 #import <Foundation/Foundation.h>  

 ///////////////////////////////////////     enum 声明     /////////////////////////////////////////////////  

 //队列优先级
 typedef enum
 {
     GlobalQueuePriorityDefault = ,
     GlobalQueuePriorityHigh = ,
     GlobalQueuePriorityLow = -,
     GlobalQueuePriorityBackground = INT16_MIN  

 } GlobalQueuePriority;  

 //阻塞、非阻塞
 typedef enum
 {
     PerformBlockFeatureChoke,
     PerformBlockFeatureUnchoke  

 } PerformBlockFeature;  

 //网络请求方法
 typedef enum GCDHelperHttpRequestMethod
 {
     GCDHelperHttpRequestMethodGET = ,
     GCDHelperHttpRequestMethodPOST  

 } GCDHelperHttpRequestMethod;  

 ///////////////////////////////////////     Block 声明     /////////////////////////////////////////////////  

 //返回值void
 typedef     void (^GCDBlock)                         (void);
 typedef     void (^GCDBlock1_Size_t)                 (size_t index);
 typedef     void (^GCDBlock1_Int)                    (int index);
 typedef     void (^GCDBlock1_Bool)                   (BOOL flag);
 typedef     void (^GCDBlock1_Float)                  (float index);
 typedef     void (^GCDBlock1_Obj)                    (id object);  

 //返回值void，两个形式参数
 typedef     void (^GCDBlock2)                        (id object1, size_t index);
 typedef     void (^GCDBlock2_Obj_Int)                (id object1, int index);
 typedef     void (^GCDBlock2_Obj_Obj)                (id object1, id object2);  

 //有返回值
 typedef     id   (^GCD_Obj_Block_Obj)                (id object);
 typedef     id   (^GCD_Obj_Block_Void)               (void);  

 typedef     void (^GCDHttpRequestBlock)              (NSURLResponse *response, NSError *error, NSData *data);  

 ///////////////////////////////////////     GCDHelper 声明     /////////////////////////////////////////////////  

 @interface GCDHelper : NSObject  

 /* 获取3种队列 */
 + (dispatch_queue_t) gcdMainQueue;
 + (dispatch_queue_t) gcdGlobalQueue:(GlobalQueuePriority) priority;
 + (dispatch_queue_t) gcdCustomQueue:(NSString *) queueName;  

 //后台执行
 + (void) gcdPerformBlockAsynchronous:(GCDBlock) block;  

 //后台获取数据后，回到主线程
 + (void) gcdPerformBlockAsynchronous:(GCDBlock) blockAsyn
                          finishOnMainQueue:(GCDBlock) blockM;  

 /* 3种队列上执行Block
  *
  * 是否阻塞执行：(PerformBlockFeature) feature
  * 全局队列优先级：(GlobalQueuePriority) priority
  */
 + (void) gcdPerformBlockOnMainQueue:(GCDBlock) block feature:(PerformBlockFeature) feature;  

 + (void) gcdPerformBlockOnGlobalQueue:(GCDBlock) block
                               feature:(PerformBlockFeature) feature
                              priority:(GlobalQueuePriority) priority;  

 + (void) gcdPerformBlockOnCustomQueue:(GCDBlock) block
                               feature:(PerformBlockFeature) feature
                                  name:(NSString *) queueName;  

 //延迟执行方法
 + (void) gcdPerformBlock:(GCDBlock) block
                  onQueue:(dispatch_queue_t) queue
              delaySecond:(int64_t) second;  

 //只执行一次
 + (void) gcdPerformBlockOnce:(GCDBlock) block;  

 //并发
 + (void) gcdBatchPerformBlocks:(NSArray *) blockArray finally:(GCDBlock) finallyBlock;  

 + (void) gcdBatchPerformBlockWithData:(NSArray *) dataArray
           maxConcurrentOperationCount:(uint) count
                           handleBlock:(GCDBlock1_Obj) block
                               finally:(GCDBlock1_Obj) finallyBlock;  

 @end  

 ///////////////////////////////////////     图片下载     /////////////////////////////////////////////////  

 @interface GCDHelper (ImageDownload)  

 - (void) gcdImageWithURLString:(NSString *) URLString;
 - (void) gcdImageWithURLString:(NSString *) URLString completion:(GCDBlock2_Obj_Obj) completion;  

 @end  

 ///////////////////////////////////////     网络请求     /////////////////////////////////////////////////  

 GCDBlock1_Bool _netWorkBlock;
 @interface GCDHelper (NetworkConnect)  

 //网络连接判断、实时监控
 - (void) gcdNetWorkGuarder:(NSString *) hostname withBlock:(GCDBlock1_Bool) block;  

 @end  

 @interface GCDHelper (HttpRequest)  

 //GCD请求网络（GET方式测试通过，POST方式测试未通过）
 - (void) gcdHttpRequestWithURL:(NSString *) URLString
                     httpMethod:(GCDHelperHttpRequestMethod) method
                         params:(NSDictionary *) params
                        timeout:(NSTimeInterval) time
                        success:(GCDHttpRequestBlock) successBlock
                           fail:(GCDHttpRequestBlock) failBlock;  

 @end 

 #import "GCDHelper.h"  

 #import <SystemConfiguration/SystemConfiguration.h>  

 #import <sys/socket.h>
 #import <netinet/in.h>
 #import <netinet6/in6.h>
 #import <arpa/inet.h>
 #import <ifaddrs.h>
 #import <netdb.h>  

 //Error
 #define GCDHelperErrorURLISNULL   [NSError errorWithDomain:@"please setup GCDHelper‘s url or urlString" code:100 userInfo:nil]
 #define GCDHelperErrorRequestISNULL  [NSError errorWithDomain:@"request can not be nil!" code:101 userInfo:nil]
 #define GCDHelperErrorFileExist    [NSError errorWithDomain:@"File Exist!" code:102 userInfo:nil]
 #define GCDHelperErrorCreateFail   [NSError errorWithDomain:@"Create File Fail!" code:103 userInfo:nil]  

 //下载的临时文件的后缀
 #define kTHDownLoadTask_TempSuffix  @".TempDownload"
 //计算下载速度的取样时间
 #define kTHDownLoadTimerInterval  2.0
 //THDispatchQueue默认的并发数
 #define kTHDispatchQueueDefaultConcurrentCount 10  

 #define kDefaultTimeoutInterval  15  

 static NSString * const BOUNDRY        = @"--------------------------7d71a819230404";  

 @implementation GCDHelper  

 - (void) dealloc
 {
     [super dealloc];
 }  

 - (id) init
 {
     if (self = [super init])
     {
     }  

     return self;
 }  

 #pragma mark -
 #pragma mark 获取队列  

 + (dispatch_queue_t) gcdMainQueue
 {
     return dispatch_get_main_queue();
 }  

 + (dispatch_queue_t) gcdGlobalQueue:(GlobalQueuePriority) priority
 {
     switch (priority)
     {
         case GlobalQueuePriorityDefault:
             return dispatch_get_global_queue(priority, );
             break;
         case GlobalQueuePriorityHigh:
             return dispatch_get_global_queue(priority, );
             break;
         case GlobalQueuePriorityLow:
             return dispatch_get_global_queue(priority, );
             break;
         case GlobalQueuePriorityBackground:
             return dispatch_get_global_queue(priority, );
             break;  

         default:
             return dispatch_get_global_queue(GlobalQueuePriorityDefault, );
             break;
     }
 }  

 + (dispatch_queue_t) gcdCustomQueue:(NSString *) queueName;
 {
     return dispatch_queue_create([queueName UTF8String], NULL);
 }  

 #pragma mark -
 #pragma mark 3种队列上执行Block  

 + (void) gcdPerformBlockOnMainQueue:(GCDBlock) block feature:(PerformBlockFeature) feature
 {
     switch (feature)
     {
         case PerformBlockFeatureChoke:
             dispatch_sync([GCDHelper gcdMainQueue], block);
             break;  

         case PerformBlockFeatureUnchoke:
             dispatch_async([GCDHelper gcdMainQueue], block);
             break;  

         default:
             dispatch_sync([GCDHelper gcdMainQueue], block);
             break;
     }
 }  

 + (void) gcdPerformBlockOnGlobalQueue:(GCDBlock) block feature:(PerformBlockFeature) feature priority:(GlobalQueuePriority) priority
 {
     switch (feature)
     {
         case PerformBlockFeatureChoke:
             dispatch_sync([GCDHelper gcdGlobalQueue:priority], block);
             break;  

         case PerformBlockFeatureUnchoke:
             dispatch_async([GCDHelper gcdGlobalQueue:priority], block);
             break;  

         default:
             dispatch_sync([GCDHelper gcdGlobalQueue:GlobalQueuePriorityDefault], block);
             break;
     }
 }  

 + (void) gcdPerformBlockOnCustomQueue:(GCDBlock) block feature:(PerformBlockFeature) feature name:(NSString *) queueName
 {
     switch (feature)
     {
         case PerformBlockFeatureChoke:
             dispatch_sync([GCDHelper gcdCustomQueue:queueName], block);
             break;  

         case PerformBlockFeatureUnchoke:
             dispatch_async([GCDHelper gcdCustomQueue:queueName], block);
             break;  

         default:
             dispatch_sync([GCDHelper gcdCustomQueue:@"com.GCDHelper.Queue"], block);
             break;
     }
 }  

 //后台执行
 + (void) gcdPerformBlockAsynchronous:(GCDBlock) block
 {
     [GCDHelper gcdPerformBlockOnGlobalQueue:block
                                     feature:PerformBlockFeatureUnchoke
                                    priority:GlobalQueuePriorityDefault];
 }  

 //后台获取数据后，回到主线程
 + (void) gcdPerformBlockAsynchronous:(GCDBlock) blockAsyn
                    finishOnMainQueue:(GCDBlock) blockM
 {
     dispatch_async([GCDHelper gcdGlobalQueue:GlobalQueuePriorityDefault], ^{
         blockAsyn();
         dispatch_async([GCDHelper gcdMainQueue], ^{
             blockM();
         });
     });
 }  

 #pragma mark -
 #pragma mark 队列延迟时间执行方法
 + (void) gcdPerformBlock:(GCDBlock) block onQueue:(dispatch_queue_t) queue delaySecond:(int64_t) second
 {
     dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, second * NSEC_PER_SEC);
     dispatch_after(popTime, queue, block);
 }  

 #pragma mark -
 #pragma mark 只执行一次  

 + (void) gcdPerformBlockOnce:(GCDBlock) block
 {
     static dispatch_once_t onceToken;
     dispatch_once(&onceToken, block);
 }  

 #pragma mark -
 #pragma mark 无序并发  

 + (void) gcdBatchPerformBlocks:(NSArray *) blockArray finally:(GCDBlock) finallyBlock
 {
     [blockArray retain];  

     dispatch_queue_t queue = [GCDHelper gcdGlobalQueue:GlobalQueuePriorityDefault];
     dispatch_group_t group = dispatch_group_create();  

     for(GCDBlock block in blockArray)
     {
         dispatch_group_async(group, queue, ^{
             block();
         });
     }
     dispatch_group_wait(group, DISPATCH_TIME_FOREVER);  

     dispatch_async([GCDHelper gcdGlobalQueue:GlobalQueuePriorityDefault], ^{
         finallyBlock();
     });  

     dispatch_release(group);  

     [blockArray release];
 }  

 + (void) gcdBatchPerformBlockWithData:(NSArray *) dataArray
           maxConcurrentOperationCount:(uint) count
                           handleBlock:(GCDBlock1_Obj) block
                               finally:(GCDBlock1_Obj) finallyBlock
 {
     [dataArray retain];  

     dispatch_queue_t queue = [GCDHelper gcdGlobalQueue:GlobalQueuePriorityDefault];
     dispatch_group_t group = dispatch_group_create();
     dispatch_semaphore_t semaphore = dispatch_semaphore_create(count);
     for(id obj in dataArray)
     {
         NSLog(@"并发中");
         dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
         dispatch_group_async(group, queue, ^{
             block(obj);
             dispatch_semaphore_signal(semaphore);
         });
     }  

     dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
     dispatch_group_notify(group, queue, ^{
         finallyBlock(dataArray);
     });
     dispatch_release(group);  

     [dataArray release];
 }  

 #pragma mark -
 #pragma mark 图片下载  

 - (void) gcdImageWithURLString:(NSString *) URLString
 {
     [self gcdImageWithURLString:URLString completion:nil];
 }  

 - (void) gcdImageWithURLString:(NSString *) URLString completion:(GCDBlock2_Obj_Obj) completion
 {
     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, ), ^{  

         NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
         [request setURL:[NSURL URLWithString:URLString]];
         [request setHTTPMethod:@"GET"];
         NSData *returnData = [NSURLConnection sendSynchronousRequest:request
                                                    returningResponse:nil
                                                                error:nil];
         [request release];  

         UIImage *image  = [UIImage imageWithData:returnData];  

         if (image)
         {
             dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, ), ^{
                 completion(image, URLString);
             });
         } else
         {
             dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, ), ^{
                 completion(image, URLString);
             });
         }
     });
 }  

 @end  

 #pragma mark -
 #pragma mark 网络部分  

 @implementation GCDHelper (NetworkConnect)  

 - (BOOL)isReachableWithFlags:(SCNetworkReachabilityFlags)flags
 {
     BOOL connectionUP = YES;  

     if(!(flags & kSCNetworkReachabilityFlagsReachable))
         connectionUP = NO;  

     if( (flags & (kSCNetworkReachabilityFlagsConnectionRequired | kSCNetworkReachabilityFlagsTransientConnection)) == (kSCNetworkReachabilityFlagsConnectionRequired | kSCNetworkReachabilityFlagsTransientConnection) )
         connectionUP = NO;  

     return connectionUP;
 }  

 -(void)reachabilityChanged:(SCNetworkReachabilityFlags)flags
 {
     dispatch_async(dispatch_get_main_queue(), ^{
         _netWorkBlock([self isReachableWithFlags:flags]);
     });
 }  

 static void TMReachabilityCallback(SCNetworkReachabilityRef target, SCNetworkReachabilityFlags flags, void* info)
 {
     @autoreleasepool
     {
         [(GCDHelper *)info reachabilityChanged:flags];
     }
 }  

 - (void) gcdNetWorkGuarder:(NSString *) hostname withBlock:(GCDBlock1_Bool) block
 {
     _netWorkBlock = block;  

     SCNetworkReachabilityRef ref = SCNetworkReachabilityCreateWithName(NULL, [hostname UTF8String]);
     SCNetworkReachabilityContext context = { , NULL, NULL, NULL, NULL };
     dispatch_queue_t queue = dispatch_queue_create("com.myself.reachability", NULL);
     context.info = (void *)self;
     SCNetworkReachabilitySetCallback(ref, TMReachabilityCallback, &context);
     SCNetworkReachabilitySetDispatchQueue(ref, queue);
 }  

 @end  

 @implementation GCDHelper(HttpRequest)  

 - (void) startPOSTHTTPRequest:(NSString *) URLString
                        params:(NSDictionary *) params
                       timeout:(NSTimeInterval) time
                       success:(GCDHttpRequestBlock) successBlock
                          fail:(GCDHttpRequestBlock) failBlock
 {
     [params retain];
     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, ), ^{  

         __block NSURLResponse  *response = nil;
         __block NSError *error = nil;
         __block NSData *receiveData = nil;  

         NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];  

         [request setURL:[NSURL URLWithString:[URLString lowercaseString]]];
         [request setHTTPMethod:@"POST"];
         [request setCachePolicy:NSURLRequestUseProtocolCachePolicy];
         [request setTimeoutInterval:time];  

         if (!request)
         {
             NSDictionary *errorInfo = [NSDictionary dictionaryWithObjectsAndKeys:@"发送请求失败", @"errorKey", nil];
             error = [NSError errorWithDomain:@"www.myself.com" code: userInfo:errorInfo];  

             dispatch_async(dispatch_get_main_queue(), ^{
                 successBlock(response, error, receiveData);
             });  

             return;
         }  

         if (params != nil)
         {
             [request setValue:[NSString stringWithFormat:@"multipart/form-data; boundary=%@", BOUNDRY]
            forHTTPHeaderField:@"Content-Type"];  

             int len=;
             NSMutableData *postData =[NSMutableData dataWithCapacity:len];
             [postData appendData:[[NSString stringWithFormat:@"--%@/r/n", BOUNDRY]
                                   dataUsingEncoding:NSUTF8StringEncoding]];
             int i=;
             int cnt = [params count];  

             for (NSString *key in [params allKeys])
             {
                 // NSString *str = [NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"/r/n/r/n", key];
                 [postData appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"/r/n/r/n", key] dataUsingEncoding:NSUTF8StringEncoding]];  

                 [postData  appendData: [[NSString stringWithFormat:@"%@",[params objectForKey:key]]
                                         dataUsingEncoding:NSUTF8StringEncoding]];
                 if(i != cnt - )
                 {
                     [postData appendData:[[NSString stringWithFormat:@"/r/n--%@/r/n", BOUNDRY]
                                           dataUsingEncoding:NSUTF8StringEncoding]];
                 }
                 i++ ;
             }
             [postData  appendData:[[NSString stringWithFormat:@"/r/n--%@--/r/n", BOUNDRY]
                                    dataUsingEncoding:NSUTF8StringEncoding]];  

             [request  setHTTPBody:postData];
         }  

         receiveData = [[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error] retain];
         if (!error)
         {
             dispatch_async(dispatch_get_main_queue(), ^{
                 successBlock(response, nil, receiveData);
             });
         }
         else
         {
             dispatch_async(dispatch_get_main_queue(), ^{
                 successBlock(response, error, receiveData);
             });
         }  

         [request release];
     });  

     [params release];
 }  

 - (void) startGETHTTPRequest:(NSString *) URLString
                       params:(NSDictionary *) params
                      timeout:(NSTimeInterval) time
                      success:(GCDHttpRequestBlock) successBlock
                         fail:(GCDHttpRequestBlock) failBlock
 {
     [params retain];  

     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, ), ^{
         __block NSURLResponse  *response = nil;
         __block NSError *error = nil;
         __block NSData *receiveData = nil;  

         NSMutableString *paramsString = [[NSMutableString alloc] init];
         for(NSString *key in params)
         {
             [paramsString appendFormat:@"&%@=%@", key, [params objectForKey:key]];
         }
         NSString *requestString = [[NSString alloc] initWithFormat:@"%@%@", URLString, paramsString];
         NSURL *reqUrl = [[NSURL alloc] initWithString:requestString];  

         [paramsString release];
         [requestString release];  

         NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];  

         [request setURL:reqUrl];
         [request setHTTPMethod:@"GET"];
         [request setCachePolicy:NSURLRequestUseProtocolCachePolicy];
         [request setTimeoutInterval:time];  

         [reqUrl release];  

         if (request)
         {
             receiveData = [[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error] retain];
         }  

         if (!error)
         {
             dispatch_async(dispatch_get_main_queue(), ^{
                 successBlock(response, nil, receiveData);
             });
         }
         else
         {
             dispatch_async(dispatch_get_main_queue(), ^{
                 successBlock(response, error, receiveData);
             });
         }  

         [request release];
     });  

     [params release];
 }  

 - (void) gcdHttpRequestWithURL:(NSString *) URLString
                     httpMethod:(GCDHelperHttpRequestMethod) method
                         params:(NSDictionary *) params
                        timeout:(NSTimeInterval) time
                        success:(GCDHttpRequestBlock) successBlock
                           fail:(GCDHttpRequestBlock) failBlock
 {
     switch (method)
     {
         case GCDHelperHttpRequestMethodGET:
         {
             [self startGETHTTPRequest:URLString params:params timeout:time success:successBlock fail:failBlock];
             break;
         }
         case GCDHelperHttpRequestMethodPOST:
         {
             [self startPOSTHTTPRequest:URLString params:params timeout:time success:successBlock fail:failBlock];
             break;
         }  

         default:
             break;
     }
 }  

 @end 

用法举例：

一、基本概念举例：

 [cpp] view plaincopyprint?

     #import <UIKit/UIKit.h>  

     @interface BaseViewController : UIViewController
     {
         IBOutlet UITextField *field1;
         IBOutlet UITextField *field2;
         IBOutlet UITextField *field3;  

         IBOutlet UITextField *textField;  

         dispatch_queue_t queue;
     }  

     - (IBAction) calculate:(id)sender;
     - (IBAction) operationQueue:(id)sender;
     - (IBAction) gcd:(id)sender;  

     - (IBAction) notchoke:(id)sender;
     - (IBAction) choke:(id)sender;  

     - (IBAction) getUIData:(id)sender;  

     - (IBAction)startQueue:(id)sender;
     - (IBAction)suspendQueue:(id)sender;
     - (IBAction)resumeQueue:(id)sender;  

     @end  

 [cpp] view plaincopyprint?

     #import "BaseViewController.h"  

     @implementation BaseViewController  

     - (void) dealloc
     {
         dispatch_release(queue);  

         [super dealloc];
     }  

     - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
     {
         self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
         if (self) {
             queue = dispatch_queue_create("sss", NULL);
         }
         return self;
     }  

     - (void)viewDidLoad
     {
         [super viewDidLoad];
         // Do any additional setup after loading the view from its nib.
     }  

     - (void) longTask:(id) sender
     {
         NSMutableArray *arr = [NSMutableArray array];
         for (int i = ; i < ; i++) {  

             [arr addObject:[NSMutableArray arrayWithObject:@(i)]];
             NSLog(@"longTask:%d", i);
         }
     }  

     - (void) longTaskOther:(id) sender
     {
         NSMutableArray *arr = [NSMutableArray array];
         for (int i = ; i < ; i++) {  

             [arr addObject:[NSMutableArray arrayWithObject:@(i)]];
             NSLog(@"longTaskOther:%d", i);
         }
     }  

     - (IBAction) calculate:(id)sender
     {
         field3.text = [NSString stringWithFormat:@"%f", [field1.text floatValue] - [field2.text floatValue]];
     }
     - (IBAction) operationQueue:(id)sender;
     {
         NSOperationQueue *aqueue = [NSOperationQueue new];
         NSInvocationOperation *operation = [[NSInvocationOperation alloc]
                                             initWithTarget:self
                                             selector:@selector(longTask:)
                                             object:nil];
         NSInvocationOperation *operation1 = [[NSInvocationOperation alloc]
                                             initWithTarget:self
                                             selector:@selector(longTaskOther:)
                                             object:nil];  

         [aqueue addOperation:operation];
         [aqueue addOperation:operation1];  

         [operation release];
         [operation1 release];
     }
     - (IBAction) gcd:(id)sender  //3.192999
     {
         [GCDHelper gcdPerformBlockAsynchronous:^{
             NSMutableArray *arr = [NSMutableArray array];
             for (int i = ; i < ; i++) {  

                 [arr addObject:[NSMutableArray arrayWithObject:@(i)]];
                 NSLog(@"longTask:%d", i);
             }
         }];  

         [GCDHelper gcdPerformBlockAsynchronous:^{
             NSMutableArray *arr = [NSMutableArray array];
             for (int i = ; i < ; i++) {  

                 [arr addObject:[NSMutableArray arrayWithObject:@(i)]];
                 NSLog(@"longTaskOther:%d", i);
             }
         }];
     }  

     //////////////////////////////////////////////////////  

     - (IBAction)notchoke:(id)sender
     {
         dispatch_async(dispatch_get_main_queue(), ^{
             NSLog(@"qqq");
         });  

         NSLog(@"不阻塞");
     }  

     //Calls to dispatch_sync() targeting the current queue will result
     //* in dead-lock. Use of dispatch_sync() is also subject to the same
     //* multi-party dead-lock problems that may result from the use of a mutex.
     //* Use of dispatch_async() is preferred.
     //在当前队列上调用dispatch_sync() 会导致死锁。调用dispatch_sync()，并使用mutex 经常会导致多方死锁问题。
     - (IBAction) choke:(id)sender
     {
         dispatch_queue_t exampleQueue;  

         int i = ;
         switch (i) {
             case :
                 exampleQueue = dispatch_get_global_queue(, );
                 break;
             case :
                 exampleQueue = dispatch_queue_create("com.abc.xxx", NULL);
                 break;
             case :
                 exampleQueue = dispatch_get_current_queue();
                 break;
             case :
                 exampleQueue = dispatch_get_main_queue();
                 break;  

             default:
                 exampleQueue = dispatch_get_global_queue(, );
                 break;
         }  

         dispatch_sync( exampleQueue,^{
             [self longTask:nil];
         });  

         NSLog(@"task finish");
     }  

     - (IBAction) getUIData:(id)sender
     {
         dispatch_async(dispatch_get_global_queue(, ), ^{  

             __block NSString *stringValue;
             dispatch_sync(dispatch_get_main_queue(), ^{
                 stringValue = [textField.text copy];
             });  

             [stringValue retain];  

             NSLog(@"stringValue:%@", stringValue);
         });
     }  

     //一个要注意的地方是，dispatch queue的挂起是block粒度的。换句话说，挂起一个queue并不会将当前正在执行的block挂起。它会允许当前执行的block执行完毕，然后后续的block不再会被执行，直至queue被恢复。
     //还有一个注意点：从man页上得来的：如果你挂起了一个queue或者source，那么销毁它之前，必须先对其进行恢复。
     - (IBAction)startQueue:(id)sender
     {
         dispatch_async(queue, ^{
             for (int i = ; i < ; i++) {
                 NSLog(@"taskA");
             }
         });  

         dispatch_async(queue, ^{
             for (int i = ; i < ; i++) {
                 NSLog(@"taskB");
             }
         });  

         dispatch_async(queue, ^{
             for (int i = ; i < ; i++) {
                 NSLog(@"taskC");
             }
         });
     }
     - (IBAction)suspendQueue:(id)sender
     {
         NSLog(@"Queue suspend");
         dispatch_suspend(queue);  

     }
     - (IBAction)resumeQueue:(id)sender
     {
         NSLog(@"Queue resume");
         dispatch_resume(queue);  

     }  

二、基本用法举例

例子1:

     #import <UIKit/UIKit.h>  

     @interface OneViewController : UIViewController  

     //无序并发
     - (IBAction)selector0:(id)sender;  

     //无序并发处理数据
     - (IBAction)selector100:(id)sender;  

     //执行一次
     - (IBAction)selector1:(id)sender;  

     //异步／后台执行
     - (IBAction)selector2:(id)sender;  

     //后台执行，然后返回主线程
     - (IBAction)selector3:(id)sender;  

     //三种队列执行
     - (IBAction)selector4:(UISegmentedControl *)sender;  

     //延迟执行
     - (IBAction)selector5:(id)sender;  

     @end  

 [cpp] view plaincopyprint?

     #import "OneViewController.h"  

     @interface OneViewController ()  

     @end  

     @implementation OneViewController  

     - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
     {
         self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
         if (self) {
             // Custom initialization
         }
         return self;
     }  

     - (void)viewDidLoad
     {
         [super viewDidLoad];
     }  

     - (NSMutableArray *) getBlockArray
     {
         NSMutableArray *arr = [[NSMutableArray array] retain];  

         GCDBlock b0 = ^{ NSLog(@"无序并发: 0"); sleep(); }; [arr addObject:b0];
         GCDBlock b1 = ^{ NSLog(@"无序并发: 1"); }; [arr addObject:b1];
         GCDBlock b2 = ^{ NSLog(@"无序并发: 2"); }; [arr addObject:b2];
         GCDBlock b3 = ^{ NSLog(@"无序并发: 3"); }; [arr addObject:b3];
         GCDBlock b4 = ^{ NSLog(@"无序并发: 4"); }; [arr addObject:b4];
         GCDBlock b5 = ^{ NSLog(@"无序并发: 5"); }; [arr addObject:b5];
         GCDBlock b6 = ^{ NSLog(@"无序并发: 6"); }; [arr addObject:b6];
         GCDBlock b7 = ^{ NSLog(@"无序并发: 7"); }; [arr addObject:b7];
         GCDBlock b8 = ^{ NSLog(@"无序并发: 8"); }; [arr addObject:b8];
         GCDBlock b9 = ^{ NSLog(@"无序并发: 9"); }; [arr addObject:b9];
         GCDBlock b10 = ^{ NSLog(@"无序并发: 10"); }; [arr addObject:b10];
         GCDBlock b11 = ^{ NSLog(@"无序并发: 11"); }; [arr addObject:b11];
         GCDBlock b12 = ^{ NSLog(@"无序并发: 12"); }; [arr addObject:b12];
         GCDBlock b13 = ^{ NSLog(@"无序并发: 13"); }; [arr addObject:b13];
         GCDBlock b14 = ^{ NSLog(@"无序并发: 14"); }; [arr addObject:b14];
         GCDBlock b15 = ^{ NSLog(@"无序并发: 15"); }; [arr addObject:b15];  

         return arr;
     }  

     //无序并发
     - (IBAction)selector0:(id)sender
     {
         [GCDHelper gcdBatchPerformBlocks:[self getBlockArray] finally:^{
             NSLog(@"一组有序并发完成");
         }];  

     //    NSLog(@"一组无序并发完成");
     }  

     - (IBAction)selector100:(id)sender
     {
         NSMutableArray *arr = [NSMutableArray array];
         for (int i = ; i < ; i++) {
             [arr addObject:[NSMutableArray array]];
         }  

         __block int i = ;
         [GCDHelper gcdBatchPerformBlockWithData:arr maxConcurrentOperationCount: handleBlock:^(id object) {  

             sleep();
             NSMutableArray *arr = (NSMutableArray *)object;
             [arr addObject:@(i)];
             i++;
         } finally:^(id object) {
             NSLog(@"arr:%@", object);
         }];
     }  

     - (IBAction)selector1:(id)sender
     {
         [GCDHelper gcdPerformBlockOnce:^{
             NSLog(@"别想让我执行第二次");
         }];
         NSLog(@"不执行～");
     }  

     //异步／后台执行
     - (IBAction)selector2:(id)sender
     {
         [GCDHelper gcdPerformBlockAsynchronous:^{
             sleep();
              NSLog(@"全局队列执行完成");
         }];
         NSLog(@"全局队列执行，不影响主队列");
     }  

     //后台执行，然后返回主线程
     - (IBAction)selector3:(id)sender
     {
         [GCDHelper gcdPerformBlockAsynchronous:^{  

             for (int i = ; i< ; i++)
             {
                 NSLog(@"全局队列执行: %d", i);
             }  

         } finishOnMainQueue:^{
             NSLog(@"回到主队列");
         }];
     }  

     //三种队列执行
     - (IBAction)selector4:(UISegmentedControl *)sender
     {
         switch (sender.selectedSegmentIndex) {
             case :
             {
                 [GCDHelper gcdPerformBlockOnMainQueue:^{
                     NSLog(@"主队列执行");
                 } feature:PerformBlockFeatureUnchoke];
                 break;
             }
             case :
             {
                 [GCDHelper gcdPerformBlockOnGlobalQueue:^{
                     NSLog(@"全局队列执行");
                 } feature:PerformBlockFeatureUnchoke priority:GlobalQueuePriorityDefault];
                 break;
             }
             case :
             {
                 [GCDHelper gcdPerformBlockOnCustomQueue:^{
                     NSLog(@"自创建队列执行");
                 } feature:PerformBlockFeatureUnchoke name:@"com.abc.bcd"];
                 break;
             }  

             default:
                 break;
         }
     }  

     //延迟执行
     - (IBAction)selector5:(id)sender
     {
         NSLog(@"延迟 2s 执行");
         [GCDHelper gcdPerformBlock:^{
             NSLog(@"执行完毕");
         } onQueue:[GCDHelper gcdMainQueue] delaySecond:];
     }  

     @end  

     #import <UIKit/UIKit.h>  

     @interface MulthreadConcurrentVC : UIViewController  

     @end  

 [cpp] view plaincopyprint?

     #import "MulthreadConcurrentVC.h"  

     /* 

      如何在GCD中快速的控制并发呢？答案就是
      dispatch_semaphore，对经常做unix开发的人来讲，我所介绍的内容可能就显得非常入门级了，信号量在他们的多线程开发中再平常不过了。
      在GCD中有三个函数是semaphore的操作，分别是：
      dispatch_semaphore_create          创建一个semaphore
      dispatch_semaphore_signal          发送一个信号
      dispatch_semaphore_wait              等待信号
      简单的介绍一下这三个函数，第一个函数有一个整形的参数，我们可以理解为信号的总量，dispatch_semaphore_signal是发送一个信号，自然会让信号总量加1，dispatch_semaphore_wait等待信号，当信号总量少于0的时候就会一直等待，否则就可以正常的执行，并让信号总量减少1，根据这样的原理，我们便可以快速的创建一个并发控制。 

      */  

     /* 

     简单的介绍一下这一段代码，创建了一个初使值为10的semaphore，每一次for循环都会创建一个新的线程，线程结束的时候会发送一个信号，线程创建之前会信号等待，所以当同时创建了10个线程之后，for循环就会阻塞，等待有线程结束之后会增加一个信号才继续执行，如此就形成了对并发的控制，如上就是一个并发数为10的一个线程队列。 

     */  

     @implementation MulthreadConcurrentVC  

     - (void) loadView
     {
         [super loadView];
     }  

     - (void)aSelector:(id)sender
     {
         dispatch_group_t group = dispatch_group_create();
         dispatch_semaphore_t semaphore = dispatch_semaphore_create();
         dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, );
         for (int i = ; i < ; i++)
         {
             dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
             dispatch_group_async(group, queue, ^{
                 NSLog(@"%i",i);
                 sleep();
                 dispatch_semaphore_signal(semaphore);
             });
         }
         dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
         dispatch_release(group);
         dispatch_release(semaphore);
     }  

     - (void)viewDidLoad
     {
         [super viewDidLoad];  

         UIButton *bt = [UIButton buttonWithType:UIButtonTypeRoundedRect];
         bt.frame = CGRectMake(, , , );
         [bt addTarget:self action:@selector(aSelector:) forControlEvents:UIControlEventTouchUpInside];
         [self.view addSubview:bt];
     }  

三、GCD实际应用举例

     #import <UIKit/UIKit.h>  

     #import "GCDHelper.h"  

     @interface TableViewController : UITableViewController  

     @end  

 [cpp] view plaincopyprint?

     #import "TableViewController.h"
     #import "CustomCell.h"
     #import <objc/runtime.h>  

     static char * const kIndexPathAssociationKey = "JK_indexPath";  

     @interface TableViewController ()  

     @end  

     @implementation TableViewController  

     - (id)initWithStyle:(UITableViewStyle)style
     {
         self = [super initWithStyle:style];
         if (self) {
             // Custom initialization
         }
         return self;
     }  

     - (void)viewDidLoad
     {
         [super viewDidLoad];  

         self.clearsSelectionOnViewWillAppear = NO;
         self.navigationItem.rightBarButtonItem = self.editButtonItem;
     }  

     - (void)didReceiveMemoryWarning
     {
         [super didReceiveMemoryWarning];
         // Dispose of any resources that can be recreated.
     }  

     #pragma mark - Table view data source  

     - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
     {
         return ;
     }  

     - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
     {
         return ;
     }  

     - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
     {
         static NSString *CellIdentifier = @"Cell";
         UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];  

         if (cell == nil) {
             cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
             UIImageView *im = [[UIImageView alloc] initWithFrame:CGRectMake(, , , )];
             im.tag = ;
             [cell addSubview:im];
             [im release];
         }  

         return cell;
     }  

     - (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
     {
     //    http://localhost:8888/Imgs/img0.png
     //    http://theme.blogcn.com/wp-content/themes/coffee-desk/images/rsscoffee.PNG  

         NSString *imgURLStr = nil;
         if ((indexPath.row % ) == )
         {
             imgURLStr = @"http://localhost:8888/Imgs/img0.png";
         } else
         {
             imgURLStr = @"http://localhost:8888/Imgs/img1.png";
         }  

         GCDHelper *hp = [GCDHelper new];
         [hp gcdImageWithURLString:imgURLStr
                        completion:^(id object1, id object2) {  

                            dispatch_async(dispatch_get_main_queue(), ^{
                                UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
                                [(UIImageView *)[cell viewWithTag:] setImage:(UIImage *)object1];
                            });
                        }];
     }  

     #pragma mark - Table view delegate  

     - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
     {
     }  

     #pragma mark -
     #pragma mark - cell重用  

     - (void)tableViewCellIsPreparingForReuse:(NSNotification *)notification
     {
         if ([[notification object] isKindOfClass:[CustomCell class]]) {
             CustomCell *cell = (CustomCell *)[notification object];  

             objc_setAssociatedObject(cell,
                                      kIndexPathAssociationKey,
                                      nil,
                                      OBJC_ASSOCIATION_RETAIN);  

             [[cell imageView] setImage:nil];
         }
     }  

     @end  

     #import <UIKit/UIKit.h>  

     extern NSString * const kJKPrepareForReuseNotification;  

     @interface CustomCell : UITableViewCell  

     @end  

 [cpp] view plaincopyprint?

     #import "CustomCell.h"  

     NSString * const kJKPrepareForReuseNotification = @"JKCallbacksTableViewCell_PrepareForReuse";  

     @implementation CustomCell  

     - (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
     {
         self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
         if (self) {
             //如果cell 的图片发生改变，当cell重用的时候，刷新图片  

             [[self imageView] addObserver:self
                                forKeyPath:@"image"
                                   options:NSKeyValueObservingOptionOld
                                   context:NULL];
         }
         return self;
     }  

     - (void)observeValueForKeyPath:(NSString *)keyPath
                           ofObject:(id)object
                             change:(NSDictionary *)change
                            context:(void *)context
     {
         NSLog(@"observeValueForKeyPath");  

         if (object == [self imageView] &&
             [keyPath isEqualToString:@"image"] &&
             ([change objectForKey:NSKeyValueChangeOldKey] == nil ||
              [change objectForKey:NSKeyValueChangeOldKey] == [NSNull null]))
         {
             [self setNeedsLayout];
         }
     }  

     - (void)prepareForReuse
     {
         [[NSNotificationCenter defaultCenter] postNotificationName:kJKPrepareForReuseNotification
                                                             object:self];  

         [super prepareForReuse];
     }
       

     #import <Foundation/Foundation.h>  

     @interface NetGuarder : NSObject  

     + (NetGuarder *) shareNetGuarder;  

     @end  

     #import "NetGuarder.h"  

     @implementation NetGuarder  

     static NetGuarder *guarder = nil;  

     + (void) getNetConnectMsg
     {
         GCDHelper *hp = [GCDHelper new];
         [hp gcdNetWorkGuarder:@"www.baidu.com" withBlock:^(BOOL flag) {
             if (flag)
             {
                 NSLog(@"Net connect");
             } else
             {
                 NSLog(@"Net not connect");
             }
         }];
     }  

     + (NetGuarder *) shareNetGuarder
     {
         static dispatch_once_t predicate;
         dispatch_once(&predicate, ^{  

             NSLog(@"单例创建");
             guarder = [[self alloc] init];  

             [NetGuarder getNetConnectMsg];
         });  

         return guarder;
     }  

     @end  

 #import <UIKit/UIKit.h>  

 @interface URLConViewController : UIViewController <NSURLConnectionDataDelegate>
 {
     IBOutlet UISegmentedControl *segment;
     IBOutlet UILabel *label;
 }  

 @end 

     #import "URLConViewController.h"  

     typedef struct _INT
     {
         int t1;  

     }INT_STRUCT;  

     @interface URLConViewController ()
     {
         NSMutableData *receivedData;
         BOOL finished;
     }  

     @end  

     @implementation URLConViewController  

     - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
     {
         self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
         if (self)
         {
             receivedData = [[NSMutableData data] retain];
         }
         return self;
     }  

     - (void)viewDidLoad
     {
         [super viewDidLoad];
     }  

     - (void)didReceiveMemoryWarning
     {
         [super didReceiveMemoryWarning];
     }  

     - (void) cleanText
     {
         label.text = @"";
     }  

     - (IBAction)segmentAction:(UISegmentedControl *)sender
     {
         switch (sender.selectedSegmentIndex) {
             case :
             {
                 [self sendRequestSync];
                 break;
             }
             case :
             {
                 [self sendRequestAsync];
                 break;
             }
             case :
             {
                 [self sendRequestAsyncOther];
                 break;
             }
             case :
             {
                 [self gcdRequest];
                 break;
             }  

             default:
                 break;
         }
     }  

     #pragma mark -
     #pragma mark  GCDRequest  

     - (void) gcdRequest
     {
         GCDHelper *hp = [GCDHelper new];  

         [hp gcdHttpRequestWithURL:@"http://localhost:8888/test.php"
                        httpMethod:GCDHelperHttpRequestMethodGET
                            params:[NSDictionary dictionary]
                           timeout:5.0f
                           success:^(NSURLResponse *response, NSError *error, NSData *data) {
                               if (data && (!error))
                               {
                                   label.text = [[data objectFromJSONData] description];
                               }  

                           }
                              fail:^(NSURLResponse *response, NSError *error, NSData *data) {
                                  if (error)
                                  {
                                      label.text = [error description];
                                  }
                              }];
     }  

     #pragma mark -
     #pragma mark  sendRequestSync  

     - (void) sendRequestSync
     {
         [self cleanText];  

         NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];  

         [request setURL:[NSURL URLWithString:@"http://localhost:8888/test.php"]];
         [request setHTTPMethod:@"GET"];  

         NSError *error = nil;
         NSData *data = [NSURLConnection sendSynchronousRequest:request
                                              returningResponse:nil
                                                          error:&error];  

         if (data && (!error))
         {
             label.text = [[data objectFromJSONData] description];
         }
     }  

     #pragma mark -
     #pragma mark  sendRequestAsync  

     - (void) sendRequestAsync
     {
         finished = NO;  

         NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
         [request setURL:[NSURL URLWithString:@"http://localhost:8888/test1.php"]];
         [request setHTTPMethod:@"GET"];
         [request setCachePolicy:NSURLRequestUseProtocolCachePolicy];
         [request setTimeoutInterval:5.0f];  

         NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request
                                                                       delegate:self
                                                               startImmediately:YES];  

         [connection start];  

     //    但是异步模式下带来了一个新的问题，很多情况下，网络请求不在主线程，或者界面等待网络结果，不在主线程的时候，调用线程如果生命周期over，下面这些可能都没有调用到，导致得不到想要得效果，所以需要在NSURLConnection请求后面加点东西来阻塞
         while(!finished) {  

             [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];  

         }
     }  

     // 收到回应
     - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
     {
         // 注意这里将NSURLResponse对象转换成NSHTTPURLResponse对象才能去
         NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;  

         if ([response respondsToSelector:@selector(allHeaderFields)])
         {
             NSDictionary *dictionary = [httpResponse allHeaderFields];
             NSLog(@"allHeaderFields: %@",dictionary);
         }
         [receivedData setLength:];
     }  

     // 接收数据
     - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
     {
         NSLog(@"get some data");
         [receivedData appendData:data];
     }  

     // 数据接收完毕
     - (void)connectionDidFinishLoading:(NSURLConnection *)connection
     {
         NSString *results = [[NSString alloc] initWithBytes:[receivedData bytes]
                                                      length:[receivedData length]
                                                    encoding:NSUTF8StringEncoding];  

         label.text = [[results objectFromJSONString] description];  

         finished = YES;
     }  

     // 返回错误
     -(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
     {
         NSLog(@"Connection failed: %@", error);
     }  

     #pragma mark -
     #pragma mark  sendRequestAsyncOther  

     - (IBAction) sendRequestAsyncOther
     {
         [self cleanText];  

         NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
         [request setURL:[NSURL URLWithString:@"http://localhost:8888/test2.php"]];
         [request setHTTPMethod:@"GET"];
         [request setCachePolicy:NSURLRequestUseProtocolCachePolicy];
         [request setTimeoutInterval:5.0f];  

         [NSURLConnection sendAsynchronousRequest:request
                                            queue:[NSOperationQueue new]
                                completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {  

                                    dispatch_async(dispatch_get_main_queue(), ^{
                                        label.text = [[data objectFromJSONData] description];
                                    });  

                                }];
     }  

     @end  

     #import <Foundation/Foundation.h>  

     /** Simple GCD-based timer based on NSTimer. 

      Starts immediately and stops when deallocated. This avoids many of the typical problems with NSTimer: 

      * RNTimer runs in all modes (unlike NSTimer)
      * RNTimer runs when there is no runloop (unlike NSTimer)
      * Repeating RNTimers can easily avoid retain loops (unlike NSTimer)
     */  

     @interface RNTimer : NSObject  

     /**---------------------------------------------------------------------------------------
      @name Creating a Timer
      -----------------------------------------------------------------------------------------
     */  

     /** Creates and returns a new repeating RNTimer object and starts running it 

      After `seconds` seconds have elapsed, the timer fires, executing the block.
      You will generally need to use a weakSelf pointer to avoid a retain loop.
      The timer is attached to the main GCD queue. 

      @param seconds The number of seconds between firings of the timer. Must be greater than 0.
      @param block Block to execute. Must be non-nil 

      @return A new RNTimer object, configured according to the specified parameters.
     */
     + (RNTimer *)repeatingTimerWithTimeInterval:(NSTimeInterval)seconds block:(dispatch_block_t)block;  

     /**---------------------------------------------------------------------------------------
      @name Firing a Timer
      -----------------------------------------------------------------------------------------
     */  

     /** Causes the block to be executed. 

      This does not modify the timer. It will still fire on schedule.
     */
     - (void)fire;  

     /**---------------------------------------------------------------------------------------
      @name Stopping a Timer
      -----------------------------------------------------------------------------------------
     */  

     /** Stops the receiver from ever firing again 

      Once invalidated, a timer cannot be reused. 

     */
     - (void)invalidate;
     @end  

    #import "RNTimer.h"  

    @interface RNTimer ()
    @property (nonatomic, readwrite, copy) dispatch_block_t block;
    @property (nonatomic, readwrite, assign) dispatch_source_t source;
    @end  

    @implementation RNTimer
    @synthesize block = _block;
    @synthesize source = _source;  

    + (RNTimer *)repeatingTimerWithTimeInterval:(NSTimeInterval)seconds
                                          block:(void (^)(void))block {
      NSParameterAssert(seconds);
      NSParameterAssert(block);  

      RNTimer *timer = [[self alloc] init];
      timer.block = block;
      timer.source = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER,
                                            , ,
                                            dispatch_get_main_queue());  

      uint64_t nsec = (uint64_t)(seconds * NSEC_PER_SEC);
      dispatch_source_set_timer(timer.source,
                                dispatch_time(DISPATCH_TIME_NOW, nsec),
                                nsec, );
      dispatch_source_set_event_handler(timer.source, block);
      dispatch_resume(timer.source);
      return timer;
    }  

    - (void)invalidate {
      if (self.source) {
        dispatch_source_cancel(self.source);
        dispatch_release(self.source);
        self.source = nil;
      }
      self.block = nil;
    }  

    - (void)dealloc {
      [self invalidate];
    }  

    - (void)fire {
      self.block();
    }  

    @end  

完整的项目链接：http://pan.baidu.com/share/link?shareid=386371&uk=3674861929

转载请保留，原文链接：http://write.blog.csdn.net/postedit/8708667

若发现有不合适或错误之处，还请批评指正，不胜感激。