读者写者编程实例

读者优先代码：
#include "stdio.h"
#include
#include


#define N_WRITER 3 //写者数目
#define N_READER 5 //读者数目
#define W_SLEEP  1 //控制写频率
#define R_SLEEP  1 //控制读频率


pthread_t wid[N_WRITER],rid[N_READER];
const int MAX_RAND = 1000;//产生的最大随机数
pthread_mutex_t writeLock = PTHREAD_MUTEX_INITIALIZER;//同一时间只能一个人写文件,互斥
pthread_mutex_t accessReaderCnt = PTHREAD_MUTEX_INITIALIZER;//同一时间只能有一个人访问 readerCnt
int data = 0;
int readerCnt = 0;
void write()
{
    int rd = rand();
    printf("write %d\n",rd);
    data = rd;
}
void read()
{
    printf("read %d\n",data);
}
void * writer(void * in)
{
    while(1)
    {
        pthread_mutex_lock(&writeLock);
        write();
        pthread_mutex_unlock(&writeLock);
        sleep(W_SLEEP);
    }
    pthread_exit((void *) 0);
}

void * reader (void * in)
{
    while(1)
    {
        pthread_mutex_lock(&accessReaderCnt);
        readerCnt++;
        if(readerCnt == 1){
            pthread_mutex_lock(&writeLock);
        }
        pthread_mutex_unlock(&accessReaderCnt);

        read();

        pthread_mutex_lock(&accessReaderCnt);
        readerCnt--;
        if(readerCnt == 0){
            pthread_mutex_unlock(&writeLock);
        }
        pthread_mutex_unlock(&accessReaderCnt);
        sleep(R_SLEEP);
    }
    pthread_exit((void *) 0);
}

int main()
{
    int i = 0;
    for(i = 0; i < N_READER; i++)
    {
        pthread_create(&wid[i],NULL,reader,NULL);
    }
    for(i = 0; i < N_WRITER; i++)
    {
        pthread_create(&rid[i],NULL,writer,NULL);
    }
    while(1){
        sleep(10);
    }
    return 0;
}
写者优先代码如下：
#include "stdio.h"
#include
#include


#define N_WRITER 2 //写者数目
#define N_READER 20 //读者数目
#define W_SLEEP 1 //控制写频率
#define R_SLEEP  0.5 //控制读频率


pthread_t wid[N_WRITER],rid[N_READER];
const int MAX_RAND = 1000;//产生的最大随机数
int data = 0;
int readerCnt = 0, writerCnt = 0;
pthread_mutex_t accessReaderCnt = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t accessWriterCnt = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t writeLock = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t readerLock = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t outerLock = PTHREAD_MUTEX_INITIALIZER;

void write()
{
    int rd = rand()%MAX_RAND;
    printf("write %d\n",rd);
    data = rd;
}
void read()
{
    printf("read %d\n",data);
}
void * writer(void * in)
{
    while(1)
    {
        pthread_mutex_lock(&accessWriterCnt);
        {//临界区,希望修改 writerCnt,独占 writerCnt
            writerCnt++;
            if(writerCnt == 1){
                //阻止后续的读者加入待读队列
                pthread_mutex_lock(&readerLock);
            }
        }
        pthread_mutex_unlock(&accessWriterCnt);


        pthread_mutex_lock(&writeLock);
        {//临界区，限制只有一个写者修改数据
            write();
        }
        pthread_mutex_unlock(&writeLock);

        pthread_mutex_lock(&accessWriterCnt);
        {//临界区,希望修改 writerCnt,独占 writerCnt
            writerCnt--;
            if(writerCnt == 0){
                //阻止后续的读者加入待读队列
                pthread_mutex_unlock(&readerLock);
            }
        }
        pthread_mutex_unlock(&accessWriterCnt);
        sleep(W_SLEEP);
    }
    pthread_exit((void *) 0);
}

void * reader (void * in)
{
    while(1)
    {
        //假如写者锁定了readerLock,那么成千上万的读者被锁在这里
        pthread_mutex_lock(&outerLock);
        {//临界区
            pthread_mutex_lock(&readerLock);//只被一个读者占有
            {//临界区
                pthread_mutex_lock(&accessReaderCnt);//代码段 1
                {//临界区
                    readerCnt++;
                    if(readerCnt == 1){
                        pthread_mutex_lock(&writeLock);
                    }
                }
                pthread_mutex_unlock(&accessReaderCnt);
            }
            pthread_mutex_unlock(&readerLock);//释放时,写者将优先获得readerLock
        }
        pthread_mutex_unlock(&outerLock);

        read();

        pthread_mutex_lock(&accessReaderCnt);//代码段2
        {//临界区
            readerCnt--;
            if(readerCnt == 0){
                pthread_mutex_unlock(&writeLock);//在最后一个并发读者读完这里开始禁止写者执行写操作
            }
        }
        pthread_mutex_unlock(&accessReaderCnt);

        sleep(R_SLEEP);
    }
    pthread_exit((void *) 0);
}

int main()
{
    int i = 0;
    for(i = 0; i < N_READER; i++)
    {
        pthread_create(&rid[i],NULL,reader,NULL);
    }
    for(i = 0; i < N_WRITER; i++)
    {
        pthread_create(&wid[i],NULL,writer,NULL);
    }
    while(1){
        sleep(10);
    }
    return 0;
}