进程间通信-----读写锁

pthread_rwlock.h

书上的源码是pthread， 但实际上应用时要改成别的名字，为了防止跟系统冲突比如 my_pthread: 

#pragma once
#include<stdlib.h>
#include<unistd.h>

#define EINVAL -1
#define EBUSY  -2

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  n>0  -1
}my_pthread_rwlock_t;

#define RW_MAGIC  0x20181126

#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_init(my_pthread_rwlock_t *rw, my_pthread_rwlockattr_t *attr)
{
    int result;
    if(attr != NULL)
        return EINVAL;
    if((result=pthread_mutex_init(&rw->rw_mutex, NULL)) != 0)
        goto err1;
    if((result=pthread_cond_init(&rw->rw_condreaders, NULL )) != 0)
        goto err2;
    if((result=pthread_cond_init(&rw->rw_condwriters, NULL)) != 0)
        goto err3;

    rw->rw_nwaitreaders = rw->rw_nwaitwriters = rw->rw_refcount = 0;
    rw->rw_magic = RW_MAGIC;
err3:
    pthread_cond_destroy(&rw->rw_condreaders);
err2:
    pthread_mutex_destroy(&rw->rw_mutex);
err1:
    return result;
}

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

    while(rw->rw_refcount<0 || rw->rw_nwaitwriters>0)
    {
        rw->rw_nwaitreaders++;
        result = pthread_cond_wait(&rw->rw_condreaders, &rw->rw_mutex);
        rw->rw_nwaitreaders--;
        if(result != 0)
            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 EINVAL;
    if((result = pthread_mutex_lock(&rw->rw_mutex)) != 0)
        return result;

    while(rw->rw_refcount != 0)
    {
        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 EINVAL;
    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 rwlock error: rw_refcount = %d\n",rw->rw_refcount);
        exit(1);
    }
    if(rw->rw_nwaitwriters > 0)
    {
        if(rw->rw_refcount == 0)
            result = pthread_cond_signal(&rw->rw_condwriters);
    }
    else if(rw->rw_nwaitreaders > 0)
        result = pthread_cond_broadcast(&rw->rw_condreaders);

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

int my_pthread_rwlock_destroy(my_pthread_rwlock_t *rw)
{
    if(rw->rw_magic != RW_MAGIC)
        return EINVAL;
    if(rw->rw_refcount!=0 || rw->rw_nwaitreaders!=0 || rw->rw_nwaitwriters!=0)
        return EBUSY;
    pthread_mutex_destroy(&rw->rw_mutex);
    pthread_cond_destroy(&rw->rw_condreaders);
    pthread_cond_destroy(&rw->rw_condwriters);
    rw->rw_magic = 0;
    return 0;
}

test.c

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

#include"pthread_rwlock.h"

my_pthread_rwlock_t rwlock = MY_PTHREAD_RWLOCK_INITIALIZER;
//my_pthread_rwlock_t rwlock;

void* thread_fun1(void *arg)
{
    my_pthread_rwlock_wrlock(&rwlock);
    printf("This is thread fun1.\n");
    sleep(3);
    my_pthread_rwlock_unlock(&rwlock);
}
void* thread_fun2(void *arg)
{
    my_pthread_rwlock_rdlock(&rwlock);
    printf("This is thread fun2. rdlock\n");
    my_pthread_rwlock_unlock(&rwlock);
}
void* thread_fun3(void *arg)
{
    my_pthread_rwlock_wrlock(&rwlock);
    printf("This is thread fun3. wrlock\n");
    my_pthread_rwlock_unlock(&rwlock);
}

int main()
{
    pthread_t tid1;
    pthread_t t1[5], t2[5];
    //my_pthread_rwlock_init(&rwlock, NULL);
    pthread_create(&tid1, NULL, thread_fun1, NULL);
    sleep(1);
    int i;
    for(i=0; i<5; ++i)
    {
        pthread_create(&t1[i], NULL, thread_fun2, NULL);
    }
    for(i=0; i<5; ++i)
    {
        pthread_create(&t2[i], NULL, thread_fun3, NULL);
    }

   // my_pthread_rwlock_destroy(&rwlock);

    pthread_join(tid1, NULL);
    for(i=0; i<5; ++i)
    {
        pthread_join(t1[i], NULL);
        pthread_join(t2[i], NULL);
    }
    return 0;
}