读写锁

作用

互斥锁在任一时刻只允许有一个线程访问关键资源, 不管是读取或写操作.
读写锁将互斥锁的功能一分为二, 分成读与写两种操作, 当进行读取操作时允许多个线程同时访问, 当进行写操作时只允许一个一个线程访问

基本函数

#include <pthread.h>
int pthread_rwlock_rdlock(pthread_rwlock_t *rwptr);
int pthread_rwlock_wdlock(pthread_rwlock_t *rwptr);
int pthread_rwlock_unlock(pthread_rwlock_t *rwptr);
int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwptr);
int pthread_rwlock_trywrlock(pthread_rwlock_t *rwptr);
 
//初始化
PTHREAD_RWLOCK_INITIALIZER
int pthread_rwlock_init(pthread_rwlock_t *rwptr,const pthread_rwlockattr_t *attr);
int pthread_rwlock_destroy(pthread_rwlock_t *rwptr);

例子

两个线程用读锁读取内容; 两个线程用写锁修改内容

#include "unpipc.h"
#include <pthread.h>
 
struct {
    pthread_rwlock_t rwlock;
    char name[20];
    int age;
} man = {
    PTHREAD_RWLOCK_INITIALIZER,"aman",20
};
 
void *showinfo(void *arg), *changeinfo(void *);
int main(int argc, char *argv[]){
    pthread_t tid1,tid2;
    pthread_create(&tid1,NULL,showinfo,NULL);
    pthread_create(&tid2,NULL,showinfo,NULL);
 
    pthread_join(tid1,NULL);
    pthread_join(tid2,NULL); 
 
    pthread_create(&tid1,NULL,changeinfo,NULL);
    pthread_create(&tid2,NULL,changeinfo,NULL);
 
    pthread_join(tid1,NULL);
    pthread_join(tid2,NULL);
 
    pthread_rwlock_destroy(&man.rwlock);
    return 0;
}
 
void *
showinfo(void *arg){
    pthread_rwlock_rdlock(&man.rwlock);
    printf("thread %ld: in showinfo
",(long)pthread_self());
    printf("name:%s,age:%d
",man.name,man.age);
    sleep(3);
    printf("thread %ld: out showinfo
",(long)pthread_self());
    pthread_rwlock_unlock(&man.rwlock);
    return NULL;
}
 
void *
changeinfo(void *arg){
    pthread_rwlock_wrlock(&man.rwlock);
    printf("thread %ld: in changeinfo
",(long)pthread_self());
    man.age=1;
    printf("name:%s,age:%d
",man.name,man.age);
    sleep(3);
    printf("thread %ld: out changeinfo
",(long)pthread_self());
    pthread_rwlock_unlock(&man.rwlock);
    return NULL;
}