iOS 線程同步-信號量 dispatch_semaphore

#define kSemaphoreBegin \
static dispatch_semaphore_t semaphore; \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
    semaphore = dispatch_semaphore_create(1); \
}); \
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

#define kSemaphoreEnd \
dispatch_semaphore_signal(semaphore);
#import "ViewController.h"
@interface ViewController ()
@property (nonatomic,assign)  int ticket;
@property (nonatomic, strong) dispatch_semaphore_t semaphore;
@property (nonatomic, strong) dispatch_semaphore_t semaphore1;
@end

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    self.semaphore = dispatch_semaphore_create(1);//最多1個線程同時執行
        self.semaphore1 = dispatch_semaphore_create(5);//最多1個線程同時執行
    self.ticket=50;
    [self ticketsTest];
//    for (int i = 0 ; i<20; i++) {
//        [[[NSThread alloc]initWithTarget:self selector:@selector(test2) object:nil] start];
//    }
    // Do any additional setup after loading the view.
}
-(void)test2{
    /*
      執行semaphore_wait 如果semaphore1 >0  semaphore1的值就會減一 並繼續往下執行
     如果semaphore1 <=0 線程就會休眠 直到 semaphore1的值>0 再將semaphore1的值就會減一 並繼續往下執行
     */
    dispatch_semaphore_wait(self.semaphore1, DISPATCH_TIME_FOREVER);
    sleep(2);
    NSLog(@"test");
    //信號量的值加一
    dispatch_semaphore_signal(self.semaphore1);
}
-(void)saleTicket{
//    static dispatch_semaphore_t semaphore;
//    static dispatch_once_t onceToken;
//    dispatch_once(&onceToken, ^{
//        semaphore=dispatch_semaphore_create(1);
//    });
//    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
//    dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
    kSemaphoreBegin
        int ticket = self.ticket;
        sleep(.2);
        ticket--;
        self.ticket=ticket;
        NSLog(@"%d-=%@",self.ticket,[NSThread currentThread]);
    kSemaphoreEnd
//    dispatch_semaphore_signal(semaphore);
//    dispatch_semaphore_signal(self.semaphore);
}
-(void)ticketsTest{
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_async(queue, ^{
        for (int i =0; i<5; i++) {
            [self saleTicket];
        }
    });
    dispatch_async(queue, ^{
        for (int i =0; i<5; i++) {
            [self saleTicket];
        }
    });
}
@end