Gcd7: execute tasks after GCD Delay

Function:

You want to specify a delay through GCD. After the delay, you can continue to execute the relevant code.

Solution:

Use the dispatch_after and dispatch_after_f Functions

Discussion:

With core Foundation, you can call the selector in the object after a given period of time. This call can use the nsobject class Optional mselector: withobject: afterdelay:Methods. In GCD, we can use the dispatch_after and dispatch_after_f functions to achieve the same purpose. The two functions are described as follows:

Dispatch_afterAfter a given time period in nanoseconds, block objects are distributed to a dispatch queue. Parameters required for this function include:

Delay in nanoseconds

Before running the specified block object, gcd must wait for the number of nanoseconds in a given dispatch Queue (specified by the second parameter.

Dispatch queue

After a given delay (specified by the first parameter), the block object must be executed on the delivery queue.

Block object

After waiting for a certain number of seconds on the specified dispatch queue, the block object will be called. It does not return a value and does not take any parameters.

  Dispatch_after_fAssign a C function to GCD and execute it after a limited time in nanoseconds. This function accepts four parameters:

Delay in nanoseconds

The number of seconds to wait.

Dispatch queue

The C function must execute the dispatch queue on the given delay.

Context
The memory address of a value passed to the C function in the heap.
C Functions
The C function that must be executed after a specific period of time.

 

The following is an example of dispatch_after:

-(Void) dispatchafter {double delayinseconds = 2.0; dispatch_time_t delayinnanoseconds =Dispatch_time (dispatch_time_now, delayinseconds *Nsec_per_sec); Dispatch_queue_t concurrentqueue = dispatch_get_global_queue (queue, 0); dispatch_after (delayinnanoseconds, concurrentqueue, ^ {nslog (@ "delayed execution ");});}

For the dispatch_after and dispatch_after_f functions, the latency parameter must be a class of dispatch_time_t, which is an abstract representation of absolute time. To get the value of this parameter, you must use the dispatch_time function shown in this Code:

Dispatch_time (dispatch_time_t when, int64_t delta)

For example, it indicates a time of 3 seconds from now on. You can write your code like this:

dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, 3.0f*NSEC_PER_SEC);

 

Now let's take a look at how to use the dispatch_after_f function:

void processSomething(void *paramContext){    /* Do your processing here */    NSLog(@"Processing...");}- (void)dispatchAfterf{    dispatch_time_t delayInNanoSenconds = dispatch_time(DISPATCH_TIME_NOW, 2.0f*NSEC_PER_SEC);    dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);    dispatch_after_f(delayInNanoSenconds, concurrentQueue, NULL, processSomething);}

 

 

 

 

Gcd7: execute tasks after GCD Delay