Linux下多线程编程简介（五）

我们已经用信号量来实现线程间的互斥，达到了互斥锁的效果，今天这篇文章将讲述怎样用信号量去实现同步。
信号量的互斥同步都是通过PV原语来操作的，我们可以通过注册两个信号量，让它们在互斥的问题上互动，从而达到同步。通过下面实例就可以很容易理解：

#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <errno.h>
#include <semaphore.h>

#define return_if_fail(p) \
if(!p) { printf("[%s]:func error!", __func__); return; }

typedef struct _PrivInfo {
sem_t sem1;
sem_t sem2;
int lock_var;
time_t end_time;
}PrivInfo;

void info_init(PrivInfo *thiz);
void info_destroy(PrivInfo *thiz);
void *pthread_function1(void *paramthiz);
void *pthread_function2(void *paramthiz);

int main (int argc, char** argv) {
pthread_t pt_1 = 0;
pthread_t pt_2 = 0;
int ret = 0;
PrivInfo *thiz = NULL;
thiz = (PrivInfo*)malloc(sizeof(PrivInfo));
if(NULL == thiz) {
return -1;
}
info_init(thiz);
ret = pthread_create(&pt_1, NULL, pthread_function1, (void*)thiz);
if(0 != ret) {
perror("pthread1 creation failed!");
}

ret = pthread_create(&pt_2, NULL, pthread_function2,(void*)thiz);
if(0 != ret) {
perror("pthread2 creation failed!");
}
pthread_join(pt_1, NULL);
pthread_join(pt_2, NULL);
info_destroy(thiz);

free(thiz);
thiz = NULL;

return 0;
}

void info_init(PrivInfo *thiz) {
return_if_fail(&thiz != NULL);
thiz->lock_var = 0;
thiz->end_time = time(NULL) + 10;
sem_init(&thiz->sem1, 0, 0);
sem_init(&thiz->sem2, 0, 1);

return;
}

void info_destroy(PrivInfo *thiz) {
return_if_fail(&thiz != NULL);
sem_destroy(&thiz->sem1);
sem_destroy(&thiz->sem2);

return;
}

void *pthread_function1(void *paramthiz) {
int i = 0;
PrivInfo *thiz = (PrivInfo *)paramthiz;
while(time(NULL) < thiz->end_time) {
sem_wait(&thiz->sem2);
printf("thread1 get the lock.\n");

sem_post(&thiz->sem1);
printf("thread1 unlock.\n");
sleep(1);
}
pthread_exit(NULL);
}

void *pthread_function2(void *paramthiz) {
PrivInfo *thiz = (PrivInfo *)paramthiz;
while(time(NULL) < thiz->end_time) {
sem_wait(&thiz->sem1);
printf("thread2 get the lock. \n");

sem_post(&thiz->sem2);
printf("thread2 unlock.\n");

sleep(1);
}

pthread_exit(NULL);
}