Block of IOS GCD

1. GCD deferred execution

#pragma mark-gcd delay/** * dispatch_after */-(void) gcddelay{NSLog (@ "Start time ....)    %@ ", [NSDate Date]);    Double delaysecond = 2.0;    dispatch_time_t delayinnanoseconds = Dispatch_time (Dispatch_time_now, delaysecond*nsec_per_sec);    Get the current global queue dispatch_queue_t Concurrentqueue = dispatch_get_global_queue (dispatch_queue_priority_default, 0);    Dispatch_after (Delayinnanoseconds, concurrentqueue, ^ (void) {NSLog (@ "Delay two seconds execution ...%@", [NSDate Date]); });}

The C function performs the following

/** * Dispatch_after_f performs a pure C function (processsomething) */-(void) gcddelay_t{NSLog (@ "Start time ....)    %@ ", [NSDate Date]);    Double delaysecond = 2.0;    dispatch_time_t delayinnanoseconds = Dispatch_time (Dispatch_time_now, delaysecond*nsec_per_sec);    Get the current global queue dispatch_queue_t Concurrentqueue = dispatch_get_global_queue (dispatch_queue_priority_default, 0); Dispatch_after_f executes a pure C function (processsomething) dispatch_after_f (delayinnanoseconds, Concurrentqueue, @ "GCD", processsomething);} void processsomething (void *paramcontext) {NSLog (@ "%@", Paramcontext);}

2.GCD single Case

-  (void) gcdsingle{    static dispatch_once_t oncetocken;         void  (^executedonlyonce) (void)  = ^{         static NSUInteger numberOfEntries = 0;         numberofentries++;        nslog (@ "Executed %lu  time (s) ",  (Unsigned long) numberofentries);    };         dispatch_queue_t concurrentqueue = dispatch_get_global_queue (DISPATCH_ queue_priority_default, 0);         dispatch_once (&onceTocken,  ^ (void) {        dispatch_async (concurrentqueue,  executedonlyonce);     });         dispatch_once ( &oncetocken, ^ (void) {&NBSp;       dispatch_async (concurrentqueue, executedonlyonce);     });     }

It can be found that the output is only one line, although we have called 2 times, because we passed the dispatch_once_t is the same, the compiler executes only once.

3.GCD Queue scheduling

/** *   problem: I use the method Dispatch_group_async for each task, is asynchronous AH. Why does the order not change?  *   answer: Because they are all assigned to the same queue Dispatch_get_main_queue ()   in! In a queue is serial ah. So, it's in order.  */-  (void) gcdgroup{    //  Create a dispatch group     dispatch_group_t  taskgroup = dispatch_group_create ();    //  Create a queue      dispatch_queue_t mainqueue = dispatch_get_main_queue ();         //  Task 1    //  adds a block to the specified dispatch group (Taskgroup), and the block uses the specified queue ( Mainqueue) execution.     dispatch_group_async (taskgroup, mainqueue, ^{         [self reloadtableview];    });         //  Task 2    //  adds a block to the specified dispatch group (Taskgroup), and the block is executed with the specified queue (mainqueue).     dispatch_group_async (Taskgroup, mainqueue, ^{        [self reloadscrollview];     });        //  Task 3    //  The block is added to the specified dispatch group (Taskgroup), and the block is executed with the specified queue (mainqueue).     dispatch_group_async (taskgroup, mainqueue, ^{         [self reloadimageview];    });         dispatch_group_notify (taskgroup, mainqueue, ^{         [[[uialertview alloc] initwithtitle:@ "complete"  message:@ "all dispatch complete"  delegate:nil  cancelbuttontitle:@ "complete"  OTHERBUTTONTITLES:NIL, NIL] SHOW];    });     }/** *   because Dispatch_group_async_f does not use block like dispatch_group_t, you can access the variables of the current class.   *  because  dispatch_group_async_f  accepts  C  functions as a block of code to execute, so we're going to execute ReloThe Adtableview method, Reloadscrollview method, Reloadimageview method, must have a reference to the current class!!!!!  *  then the  C  function must have a   reference to  self, which  Self  be able to invoke an instance method of the current object  * *//**  *  c function  */-  (void) gcdgroup_c{    //  Create a dispatch group      dispatch_group_t taskgroup = dispatch_group_create ();    //  Create queue     dispatch_queue_t mainqueue = dispatch_get_main_queue ();     dispatch_group_async_f (taskgroup, mainqueue,  (__bridge void *) self,  reloadallcomponents);     }void reloadallcomponents (Void *context) {     ViewController *self =  (__bridge viewcontroller *) context;     [self reloadTableView];    [self reloadScrollView];     [self reloadimageview];}

4. Custom Queue scheduling

-  (void) gcdcustomegroup{    dispatch_queue_t firstserialqueue =  Dispatch_queue_create ("COM.SINOICITY.GCD",  null);         dispatch _async (firstserialqueue, ^{        nsuinteger counter =  0;        for  (counter = 0; counter  < 5; counter++) {            nslog (@ " First iteration, counter = %lu ",  (unsigned long) counter);         }        nslog (@ "Current thread  = %@ ",  [nsthread currentthread]);     });         dispatch_async (firstserialqueue, ^{         nsuinteger counter = 0;        for  (counter = 0; counter <  5; counter++) {            nslog (@ " Second iteration, counter = %lu ",  (unsigned long) counter);         }        nslog (@ "Current thread  = %@ ",  [nsthread currentthread]);     });     Dispatch_async (firstserialqueue, ^{        nsuinteger  counter = 0;        for  (counter = 0;  counter < 5; counter++) {             nslog (@ "Third iteration, counter = %lu",  (unsigned long) counter);         }        nslog (@ "current thread = %@",  [NSThread  currentthread]);     });    dispatch_queue_t mainqueue  = dispatch_get_main_queue ();     dispatch_async (mainqueue, ^{         nslog (@ "main thread = %@",  [nsthread mainthread]);     });}

Note: Our custom queues are often not executed in the main queue. Instead, a single thread is allocated to maintain the queues we define.

This article is from the "one-mind" blog, please be sure to keep this source http://5007671.blog.51cto.com/4997671/1590715

Block of IOS GCD