Linux使用互斥锁和条件变量实现读写锁（读优先）

本篇博客结合上篇读写锁（写优先）

//my_pthread_rwlock.h

#pragma once

#include
#include

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

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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