linux programming---thread---read-write lock

Read-write locks communication mechanisms

write lock into read and write locks, the following functions
(1) If a thread is applied for a read lock, other threads can request read locks, but can not apply for a write lock.
(2) If a thread applies for a write lock, other threads cannot apply for a read lock or write lock.

Initializing write lock
int to pthread_rwlock_init (pthread_rwlock_t the restrict rwlock is acquired *,
            const pthread_rwlockattr_t the restrict * attr);
            
destruction write lock
int pthread_rwlock_destroy (pthread_rwlock_t * rwlock);

applying a read lock
int the pthread_rwlock_rdlock (pthread_rwlock_t * rwlock is acquired);
int pthread_rwlock_tryrdlock (pthread_rwlock_t * rwlock is acquired);

Apply for write lock
int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);

unlock
int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);

program example:
程序实现4个线程，两个读线程，两个写线程。

#include<unistd.h>
#include<stdio.h>
#include<errno.h>
#include<pthread.h>
#include<stdlib.h>
#include<string.h>
#include<pthread.h>

static pthread_rwlock_t rwlock;
#define BUFSIZE 1024
char gdata[BUFSIZE];
int gtime;

void *thread_fun_read1(void*arg);
void *thread_fun_read2(void*arg);
void *thread_fun_write1(void*arg);
void *thread_fun_write2(void*arg);


int main(int argc,char* argv[])
{
    int res;
    pthread_t th1,th2,th3,th4;
    void* thret;
    
    res = pthread_rwlock_init(&rwlock,NULL);
    if(res != 0)
    {
        perror("rwlock initialization failed");
        exit(-1);
    }
    
    res = pthread_create(&th1,NULL,thread_fun_read1,NULL);
    if(res != 0)
    {
        perror("thread create failed");
        exit(-1);
    }
    
    res = pthread_create(&th2,NULL,thread_fun_read2,NULL);
    if(res != 0)
    {
        perror("thread create failed");
        exit(-1);
    }

    res = pthread_create(&th3,NULL,thread_fun_write1,NULL);
    if(res != 0)
    {
        perror("thread create failed");
        exit(-1);
    }

    res = pthread_create(&th4,NULL,thread_fun_write2,NULL);
    if(res != 0)
    {
        perror("thread create failed");
        exit(-1);
    }

    res = pthread_join(th1,&thret);
    if(res != 0)
    {
        perror("thread join failed");
        exit(-1);
    }

    res = pthread_join(th2,&thret);
    if(res != 0)
    {
        perror("thread join failed");
        exit(-1);
    }

    res = pthread_join(th3,&thret);
    if(res != 0)
    {
        perror("thread join failed");
        exit(-1);
    }

    res = pthread_join(th4,&thret);
    if(res != 0)
    {
        perror("thread join failed");
        exit(-1);
    }
    
    pthread_rwlock_destroy(&rwlock);
    exit(0);        
}

void *thread_fun_read1(void*arg)
{
    printf("thread read one try to get lock\n");
    pthread_rwlock_rdlock(&rwlock);
    while(strncmp("end",gdata,3) != 0)
    {
        printf("this is thread read one. %s \n",gdata);
        pthread_rwlock_unlock(&rwlock);
        sleep(2);
        pthread_rwlock_rdlock(&rwlock);
        while(gdata[0] == '\0')
        {
            pthread_rwlock_unlock(&rwlock);
            sleep(2);
            pthread_rwlock_rdlock(&rwlock);
        }
    }
    pthread_rwlock_unlock(&rwlock);
    gtime = 1;
    pthread_exit(0);    
}

void *thread_fun_read2(void*arg)
{
    printf("thread read two try to get lock\n");
    pthread_rwlock_rdlock(&rwlock);
    while(strncmp("end",gdata,3) != 0)
    {
        printf("this is thread read two. %s \n",gdata);
        pthread_rwlock_unlock(&rwlock);
        sleep(5);
        pthread_rwlock_rdlock(&rwlock);
        while(gdata[0] == '\0')
        {
            pthread_rwlock_unlock(&rwlock);
            sleep(5);
            pthread_rwlock_rdlock(&rwlock);
        }
    }
    pthread_rwlock_unlock(&rwlock);
    gtime = 1;
    pthread_exit(0);    
}

void *thread_fun_write1(void*arg)
{
    printf("this is write thread one try to get lock\n");
    while(!gtime)
    {
        pthread_rwlock_wrlock(&rwlock);
        printf("this is write thread one.\n input some text,enter 'end'to finish\n");
        fgets(gdata,BUFSIZE,stdin);
        pthread_rwlock_unlock(&rwlock);
        sleep(15);
    }
    pthread_rwlock_unlock(&rwlock);
    pthread_exit(0);
}

void *thread_fun_write2(void*arg)
{
    printf("this is write thread two try to get lock\n");
    while(!gtime)
    {
        pthread_rwlock_wrlock(&rwlock);
        printf("this is write thread two.\n input some text,enter 'end'to finish\n");
        fgets(gdata,BUFSIZE,stdin);
        pthread_rwlock_unlock(&rwlock);
        sleep(15);
    }
    pthread_rwlock_unlock(&rwlock);
    pthread_exit(0);
}