C++多线程-顺序锁

原创

wx5d0241bb88268 2021-08-18 02:28:57 博主文章分类：C++ ©著作权

©著作权归作者所有：来自51CTO博客作者wx5d0241bb88268的原创作品，请联系作者获取转载授权，否则将追究法律责任

在互斥数据访问中有一种多读少写的情况。正对这么一种情形，我们也提出了读写锁的方案。但是呢，这个锁有些缺陷。什么缺陷呢？那就是，这个写锁需要在所有的读锁完成之后才能写。否则的话，写锁需要这么一直等下去。
那么，有没有什么办法能使得写操作快速一点进行呢？那就是顺序锁。

typedef struct _SEQUENCE_LOCK  
{  
    unsigned int sequence;  
    HANDLE hLock;  
  
}SEQUENCE_LOCK;

有了这么一个数据结构之后。那么读锁怎么开始呢，

unsigned int get_lock_begin(SEQUENCE_LOCK* hSeqLock)  
{  
    assert(NULL != hSeqLock);  
  
    return hSeqLock->sequence;      
}     
   
int get_lock_retry(SEQUENCE_LOCK* hSeqLock, unsigned int value)  
{  
    unsigned int new_value;  
    assert(NULL != hSeqLock);  
  
    new_value = hSeqLock->sequence;  
    return (new_value & 0x1) || (new_value ^ value);      
}

自然写锁也需要修改了，

void get_write_lock(SEQUENCE_LOCK* hSeqLock)  
{  
    assert(NULL != hSeqLock);  
  
    WaitForSingleObject(hSeqLock->hLock);  
    hSeqLock->sequence ++;  
}   
  
void release_write_lock(SEQUENCE_LOCK* hSeqLock)  
{  
    assert(NULL != hSeqLock);  
  
    hSeqLock->sequence ++;  
    ReleaseMutex(hSeqLock->hLock);  
}

如果应用呢，其实也不难，

void read_process(SEQUENCE_LOCK* hSeqLock)  
{  
    unsigned int sequence;  
  
    do{  
       sequence = get_lock_begin(hSeqLock);  
       /* read operation  */  
    }while(get_lock_retry(hSeqLock, sequence));  
}  
  
void write_process(SEQUENCCE_LOCK* hSeqLock)  
{  
    get_write_lock(hSeqLock);  
    /* write operation */  
    release_write_lock(hSeqLock);  
}