GCD 实现生产-消费 模式

#import "ViewController.h"

@interface ViewController (){

}
@property (nonatomic,strong)    dispatch_semaphore_t sema;

@end

@implementation ViewController

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

     _sema = dispatch_semaphore_create(1);
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_queue_create("custom_dis", 0);

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        if (![[NSThread currentThread]  isMainThread]) {
            NSLog(@"===异步线程===============");
        }

         for (int i = 0; i<10; i++) {

             dispatch_semaphore_wait(_sema, DISPATCH_TIME_FOREVER);

             dispatch_group_async(group, queue, ^{
                 if (![[NSThread currentThread]  isMainThread]) {
                     NSLog(@"===异步线程===============");
                 }

                 [self doCustomSomting];

             });

         }

     });

    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);

}

-(void)doCustomSomting{

    sleep(2);

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        if (![[NSThread currentThread]  isMainThread]) {
            NSLog(@"===异步线程===============");
        }
        sleep(1);

        dispatch_async(dispatch_get_main_queue(), ^{

            if ([[NSThread currentThread]  isMainThread]) {
                NSLog(@"===主线程===============");
            }
            NSLog(@"=====compeletSomting=========");

            dispatch_semaphore_signal(_sema);

        });

    });

}

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

@end