Linuxは反発ロックと条件変数を用いて読み書きロックを実現する(読み書き優先)
2885 ワード
本編ブログは前編の読み書きロック(書く優先)に合わせて
主関数は前編に似ている
//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) // 0
return result;
while(rw->rw_refcount < 0 ) //
{
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) //
{
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.
", 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;
}
主関数は前編に似ている