[iOS/Objective-C] To run threads sequentialy or concurrently

[iOS/Objective-C]에서 thread를 순차적으로 처리하기.

Thread starts when the other Thread ends [on iOS/Objective-C]

여러가지 방법이 있겠지만.... 세마포어를 사용하면 간단하다.

There are so many way to do. but, you had better to use semaphore.

1. Create semaphore

dispatch_semaphore_t sema =  dispatch_semaphore_create(0);

2. Do Thread

dispatch_async(......, ^ {

  // Do something

........

dispatch_semaphore_signal(sema);

)};

3. Wait for semaphore signal

dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);

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[iOS/Objective-C]에서 thread들을 병렬로 처리하고 모든 thread가 끝났을때 noti 받기

Process Threads concurrently and then, receive all-threads-done notification. 

1. Create dispatch_group

dispatch_group_t taskGroup = dispatch_group_create();

2.Dispatch group async each threads 

dispatch_group_async(taskGroup,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {

[NSThread sleepForTimeInterval:10.0];

});

dispatch_group_async(taskGroup,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {

[NSThread sleepForTimeInterval:5.0];

});

3. Receive notification

dispatch_group_notify(taskGroup,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {

  // something to do after two tasks...

});

-------------------------------------------------------------------------

Example

 - 순차적으로 2가지 Thread를 돌리는 Thread와, 5초동안 수행되는 1 Thread를 병렬로 처리하기. 

 - To run two threads concurrently. one is running two inner threads sequentially and another is running 5 seconds.

- (IBAction)btnClicked:(id)sender {
    dispatch_group_t taskGroup = dispatch_group_create();
    dispatch_group_async(taskGroup,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {    
        dispatch_semaphore_t sema =  dispatch_semaphore_create(0);
        [[YOUR_TASK_FIRST doWithCompleteBlock:^(BOOL success) {
            if (success) {
                [[YOUR_TASK_SECOND doWithCompleteBlock:^(BOOL success) {
                    // DO something...
                }];
                dispatch_semaphore_signal(sema);
            }
        }];
        
        dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
 
        [[YOUR_TASK_ANOTHER doWithCompleteBlock:^(BOOL success) {
            if (success) {
                    // DO something...
            }
        }];
        
        dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
 
    });
    
    dispatch_group_async(taskGroup,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
        [NSThread sleepForTimeInterval:5.0];
    });
    
    dispatch_group_notify(taskGroup,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
        // something to do after two tasks...
    });
}