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(1) 信号量定义与初始化：

semaphore rmutex = 1, wmutex = 1, readTry = 1, resource = 1;
int readCount = 0, writeCount = 0;

(2) 读者进程：

void reader() {
    P(readTry);
    P(rmutex);
    readCount++;
    if (readCount == 1) P(resource);
    V(rmutex);
    V(readTry);
    // read file...
    P(rmutex);
    readCount--;
    if (readCount == 0) V(resource);
    V(rmutex);
}

(3) 写者进程：

void writer() {
    P(wmutex);
    writeCount++;
    if (writeCount == 1) P(readTry);
    V(wmutex);
    P(resource);
    // write file...
    V(resource);
    P(wmutex);
    writeCount--;
    if (writeCount == 0) V(readTry);
    V(wmutex);
}

(4) 信号量作用：
readTry 实现写者优先，resource 控制文件访问互斥，rmutex/wmutex 保护计数器。确保有写者等待时新读者阻塞，写者不会饿死。

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