原文

• @synchronized(self){}

- (void)synchronizadTest2 {
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSLog(@"線程A，準(zhǔn)備好");
        @synchronized(self){
            NSLog(@"線程A lock, 請等待");
            [NSThread sleepForTimeInterval:3];
            NSLog(@"線程A 執(zhí)行完畢");
        }
        
    });
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSLog(@"線程B，準(zhǔn)備好");
        //相當(dāng)于 對(duì)整個(gè) 對(duì)象 都加鎖
        @synchronized(self){
            NSLog(@"線程B lock, 請等待");
            [NSThread sleepForTimeInterval:1];
            NSLog(@"線程B 執(zhí)行完畢");
        }
    });
}

>打印結(jié)果
2017-03-17 11:30:47.312 同步鎖[3600:51507] 線程B，準(zhǔn)備好
2017-03-17 11:30:47.312 同步鎖[3600:51506] 線程A，準(zhǔn)備好
2017-03-17 11:30:47.313 同步鎖[3600:51507] 線程B lock, 請等待
2017-03-17 11:30:48.382 同步鎖[3600:51507] 線程B 執(zhí)行完畢
2017-03-17 11:30:48.383 同步鎖[3600:51506] 線程A lock, 請等待
2017-03-17 11:30:51.452 同步鎖[3600:51506] 線程A 執(zhí)行完畢

• @synchronized(obj){}

- (void)synchronizadTest {
    
    
    static NSObject *lock = nil;
    
    if (!lock) {
        lock = [[NSString alloc] init];
        
    }
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSLog(@"線程A，準(zhǔn)備好");
        @synchronized(lock){
            NSLog(@"線程A lock, 請等待");
            [NSThread sleepForTimeInterval:3];
            NSLog(@"線程A 執(zhí)行完畢");
        }
        
    });
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSLog(@"線程B，準(zhǔn)備好");
        @synchronized(lock){
            NSLog(@"線程B lock, 請等待");
            [NSThread sleepForTimeInterval:1];
            NSLog(@"線程B 執(zhí)行完畢");
        }
    });
}
打印結(jié)果
2017-03-17 11:32:17.982 同步鎖[3626:52584] 線程B，準(zhǔn)備好
2017-03-17 11:32:17.982 同步鎖[3626:52587] 線程A，準(zhǔn)備好
2017-03-17 11:32:17.983 同步鎖[3626:52584] 線程B lock, 請等待
2017-03-17 11:32:19.053 同步鎖[3626:52584] 線程B 執(zhí)行完畢
2017-03-17 11:32:19.053 同步鎖[3626:52587] 線程A lock, 請等待
2017-03-17 11:32:22.124 同步鎖[3626:52587] 線程A 執(zhí)行完畢

• lock

- (void)NSLookTest {
    
    static NSLock *lock = nil;
    if (!lock) {
        lock = [[NSLock alloc] init];
    }
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSLog(@"線程A，準(zhǔn)備好");
        [lock lock];
        NSLog(@"線程A lock, 請等待");
        [NSThread sleepForTimeInterval:3];
        NSLog(@"線程A 執(zhí)行完畢");
        // 這里如果注釋了 其他地方 就不能訪問了
        [lock unlock];
    });
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSLog(@"線程B，準(zhǔn)備好");
        [lock lock];
        NSLog(@"線程B lock, 請等待");
        [NSThread sleepForTimeInterval:1];
        NSLog(@"線程B 執(zhí)行完畢");
        [lock unlock];
    });
    
}