Linux使用互斥锁和条件变量实现读写锁（读优先）

最新推荐文章于 2025-09-08 15:49:03 发布

原创最新推荐文章于 2025-09-08 15:49:03 发布 · 1k 阅读

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CC 4.0 BY-SA版权

文章标签：

#rwlock #mutex #cond #Linux

本文介绍了一种自定义读写锁的实现方式，通过使用互斥锁和条件变量来控制多个读操作或单一写操作对共享资源的访问。详细展示了读锁、写锁及解锁的函数逻辑。

本篇博客结合上篇读写锁（写优先）

//my_pthread_rwlock.h

#pragma once

#include<pthread.h>
#include<stdio.h>

typedef struct
{
    pthread_mutex_t rw_mutex;
    pthread_cond_t  rw_condreaders;
    pthread_cond_t  rw_condwriters;
    int             rw_magic;
    int             rw_nwaitreaders;
    int             rw_nwaitwriters;
    int             rw_refcount;       // 0 >0 ==-1
}my_pthread_rwlock_t;

#define  RW_MAGIC  0x20180326

#define MY_PTHREAD_RWLOCK_INITIALIZER {PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, PTHREAD_COND_INITIALIZER,\
RW_MAGIC,0,0,0}

typedef int  my_pthread_rwlockattr_t;

int my_pthread_rwlock_rdlock(my_pthread_rwlock_t *rw);
int my_pthread_rwlock_wrlock(my_pthread_rwlock_t *rw);
int my_pthread_rwlock_unlock(my_pthread_rwlock_t *rw);

//my_pthread_rwlock.c

#include"my_pthread_rwlock.h"
#include<pthread.h>

int my_pthread_rwlock_rdlock(my_pthread_rwlock_t *rw)
{
    int result;
    if(rw->rw_magic != RW_MAGIC)
        return -1;
    if((result = pthread_mutex_lock(&rw->rw_mutex)) != 0)  //锁成功返回0
        return result;

    while(rw->rw_refcount < 0 ) //被写锁占用或者读锁优先的情况
    {
        rw->rw_nwaitreaders++;
        result = pthread_cond_wait(&rw->rw_condreaders,&rw->rw_mutex);
        rw->rw_nwaitreaders--;
        if(result != 1)
            break;
    }
    if(result == 0)
        rw->rw_refcount++;

    pthread_mutex_unlock(&rw->rw_mutex);
    return result;
}

int my_pthread_rwlock_wrlock(my_pthread_rwlock_t *rw)
{
    int result;
    if(rw->rw_magic != RW_MAGIC)
        return -1;
    if((result = pthread_mutex_lock(&rw->rw_mutex)) != 0)
        return result;

    while(rw->rw_refcount != 0)    //有读时不能写
    {
        rw->rw_nwaitwriters++;
        result = pthread_cond_wait(&rw->rw_condwriters, &rw->rw_mutex);
        rw->rw_nwaitwriters--;
        if(result != 0)
            break;
    }

    if(result == 0)
        rw->rw_refcount = -1;

    pthread_mutex_unlock(&rw->rw_mutex);
        return result;
}

int my_pthread_rwlock_unlock(my_pthread_rwlock_t *rw)
{
    int result;
    if(rw->rw_magic != RW_MAGIC)
        return -1;
    if((result = pthread_mutex_lock(&rw->rw_mutex)) != 0)
        return result;

    if(rw->rw_refcount > 0)
        rw->rw_refcount--;
    else if(rw->rw_refcount == -1)
        rw->rw_refcount = 0;
    else
        printf("unlock error.\n", rw->rw_refcount);

    if(rw->rw_nwaitreaders > 0)
        result = pthread_cond_broadcast(&rw->rw_condreaders);
    else if(rw->rw_nwaitwriters > 0)
    {
        if(rw->rw_refcount == 0)
            result = pthread_cond_signal(&rw->rw_condwriters);
    }
    pthread_mutex_unlock(&rw->rw_mutex);
    return result;
}

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