1. synchronized
   static NSString* A = @"A";

   /** B鎖 /
   static NSString B = @"B";
   dispatch_async(queue, ^{
   // NSLog(@"%@",[self sourceOut]) ;
   @synchronized(A){
   NSLog(@"鎖A0");
   sleep(2);
   @synchronized(B){
   NSLog(@"鎖B0");
   }
   }
   });

   dispatch_async(queue, ^{
   @synchronized(B){
   NSLog(@"鎖B1");

        @synchronized(A){
            NSLog(@"鎖A1");
        }
    }
   

   });
   打?。?018-04-06 15:35:56.206903+0800 COCOCOCO[13309:566143] 鎖A0
   2018-04-06 15:35:56.206939+0800 COCOCOCO[13309:566145] 鎖B1

2. NSLock
   [self.lock lock];
   [self.lock lock];//由于當前線程加鎖，現(xiàn)在再次加同樣的鎖，需等待當前線程解鎖，把當前線程掛起，不能解鎖
   [_lock unlock];
   [_lock unlock];

3. 遞歸鎖。 核心：允許同一個線程對一把鎖進行重復加鎖。 如果不是同一線程那么將死鎖

• (void)__initMutexLock:(pthread_mutex_t *)mutex{
  // 遞歸鎖：允許同一個線程對一把鎖進行重復加鎖

  // 初始化屬性
  pthread_mutexattr_t attr;
  pthread_mutexattr_init(&attr);
  pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
  // 初始化鎖
  pthread_mutex_init(mutex, &attr);
  // 銷毀屬性
  pthread_mutexattr_destroy(&attr);
  }

• (void)viewDidLoad {
  [super viewDidLoad];

  [self __initMutexLock:&_MutexLock];

  dispatch_async(dispatch_get_global_queue(0, 0), ^{
  pthread_mutex_lock(&_MutexLock);
  NSLog(@"加鎖 %s =11111== %@",func, [NSThread currentThread]);

    dispatch_sync(dispatch_get_main_queue(), ^{
        pthread_mutex_lock(&_MutexLock);
        NSLog(@"加鎖 %s   =22222== %@",__func__, [NSThread currentThread]);
        NSLog(@"解鎖 %s   ==2222222= %@",__func__, [NSThread currentThread]);
        pthread_mutex_unlock(&_MutexLock);
    });
  
    NSLog(@"解鎖 %s   ==11111111= %@",__func__, [NSThread currentThread]);
  
    pthread_mutex_unlock(&_MutexLock);
  

  });
  }

2020-12-30 19:34:27.331898+0800 iOS-LockDemo[19500:315177] 加鎖 -[ViewController viewDidLoad]_block_invoke =11111== <NSThread: 0x600002d107c0>{number = 5, name = (null)}