读者写者问题

Posted on Edited on Symbols count in article: 1.1k Reading time ≈ 1 mins.

经典读者写者问题

读者写者问题

1、读者优先
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int readcount=0; 
semaphore RCSignal=1, fileSrc=1;
// RCSignal readcount修改互斥量
// fileSrc 文件资源互斥量：实现读者优先

// 读者进程：
    P(RCSignal);
    readcount++;    
    if (readcount == 1)
        P(fileSrc);
    V(RCSignal);
    // ...
    // reading is performed
    // ...
    P(RCSignal);
    readcount--;
    if (readcount == 0)
        V(fileSrc);
    V(RCSignal);
 
// 写者进程：     
    P(fileSrc);
    //...
    //writing is performed
    //...
    V(fileSrc);
2、写者优先
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int readcount=0, writecount=0; 
semaphore RCSignal=1, WCSignal=1, read=1, fileSrc;
// RCSignal readcount修改互斥量
// WCSignal writecount修改互斥量
// read 实现写者优先：拦截读者
// fileSrc 文件资源互斥量：保护剩余读者（拦截写者），以及写者唯一

// 读者进程：
P(read);
    P(RCSignal);
        readcount++;
        if(readcount == 1 ) 
            P(fileSrc);
    V(RCSignal);
V(read);
    // ...
    // reading is performed
    // ...
P(RCSignal);
    readcount--;
    if (readcount == 0 )
        V(fileSrc);
V(RCSignal);

// 写者进程：     
P(WCSingal);
    writecount++;
    if (writecount == 1 )
        P(read);
V(WCSingal);
P(fileSrc);
    // writing is performed
V(fileSrc);
P(WCSingal);
    writecount --;
    if (writecount == 0)
        V(read);
V(WCSingal);
参考资料

https://www.bilibili.com/video/av21593625 https://blog.csdn.net/c1194758555/article/details/52805918 https://blog.csdn.net/william_munch/article/details/84256690 （有问题？）