在目标c中使用@synchronized指令产生死锁和活动锁问题

@synchronized(bObj) {

    // do sth with the aObj and bObj here     
} 

 // do sth with the aObj and bObj here

Thread A        Thread B
========        ========
lock a          lock b
lock b          lock a

B

a

b

 @synchronized(MIN(a, b))
    {
        @synchronized(MAX(a, b))
        {
            // do stuff, safely
        }
    }

 NSLock *a = [[NSLock alloc] init];
    NSLock *b = [[NSLock alloc] init];

    [MIN(a, b) lock];
    [MAX(a, b) lock];

    [MAX(a, b) unlock];
    [MIN(a, b) unlock];

@synchronized (obj1) { ... }
@synchronized (obj2) { ... }