C++多线程信号量

[fly2sky]

正在学习linux多线程，写了个小小程序，实现的是两个线程往缓冲区里写数据，两个从缓冲区里读数据，效果是达到了，想写写小博记录巩固一下，但是写之前心里看程序总是不踏实，觉得领会错了写了小博反而误人子弟，望高手给指出一下是不是有问题，或者隐含的bug，或者如何改进，或者提些建议，谢谢。

#include<stdio.h>
#include<pthread.h>
#include<semaphore.h>
#define SIZE 4
struct product
{
        sem_t sem_empty;\\定义两个信号量，防止下标访问越界，和线程同步问题
        sem_t sem_full;
        pthread_mutex_t mutexlock; 
        int pos;
        int buf[SIZE];
};

void init(struct product *t)
{
        pthread_mutex_init(&t->mutexlock,NULL);
        sem_init(&t->sem_full,0,SIZE);
        sem_init(&t->sem_empty,0,0);
        t->pos =-1;
}

void put(struct product *t,int data)
{
        sem_wait(&t->sem_full);
        pthread_mutex_lock(&t->mutexlock);
        t->pos = t->pos +1;
        t->buf[t->pos] = data;
        printf("Thread %d put a data:%d to pos%d\n",pthread_self(),data,t->pos);
        sem_post(&t->sem_empty);
        pthread_mutex_unlock(&t->mutexlock);
}

void get(struct product *t)
{
        sem_wait(&t->sem_empty);
        pthread_mutex_lock(&t->mutexlock);
        printf("Thread %d get a data:%d from pos%d\n",pthread_self(),t->buf[t->pos],t->pos);
        t->buf[t->pos] = -1;
        t->pos = t->pos -1;
        sem_post(&t->sem_full);
        pthread_mutex_unlock(&t->mutexlock);
}

struct product pdt;
void *putter()
{
        int n;
        for(n=0;n<8;n++)
                put(&pdt,n);
}
void *getter()
{
        int n;
        for(n=0;n<8;n++)
                get(&pdt);
}


int main(void)
{
        pthread_t pt1,pt2,gt1,gt2;
        void *retval;
        init(&pdt);
        pthread_create(&pt1,NULL,putter,0);
        pthread_create(&pt2,NULL,putter,0);
        pthread_create(>1,NULL,getter,0);
        pthread_create(>2,NULL,getter,0);

        pthread_join(pt1,&retval);
        pthread_join(pt2,&retval);
        pthread_join(gt1,&retval);
        pthread_join(gt2,&retval);
        return 0;
}

[HTJOY]

没啥问题，挺好的

[fly2sky]

gdb我也是刚学，刚刚在用gdb运行了一下，貌似有下标越界了，SIZE为4啊，为何出来4,5,6,7了啊 (gdb) r Starting program: /home/test/program/mt3 [Thread debugging using libthread_db enabled] [New Thread -1208256832 (LWP 21728)] [New Thread -1208259664 (LWP 21729)] Thread -1208259664 put a data:0 to pos0 [New Thread -1218749520 (LWP 21730)] Thread -1208259664 put a data:1 to pos1 Thread -1208259664 put a data:2 to pos2 Thread -1208259664 put a data:3 to pos3 [New Thread -1229243472 (LWP 21731)] Thread -1218749520 put a data:0 to pos4 Thread -1208259664 put a data:4 to pos5 Thread -1229243472 get a data:4 from pos5 Thread -1218749520 put a data:1 to pos5 Thread -1229243472 get a data:1 from pos5 Thread -1208259664 put a data:5 to pos5 Thread -1229243472 get a data:5 from pos5 Thread -1218749520 put a data:2 to pos5 Thread -1229243472 get a data:2 from pos5 Thread -1208259664 put a data:6 to pos5 Thread -1229243472 get a data:6 from pos5 Thread -1218749520 put a data:3 to pos5 Thread -1229243472 get a data:3 from pos5 Thread -1208259664 put a data:7 to pos5 Thread -1229243472 get a data:7 from pos5 Thread -1218749520 put a data:4 to pos5 Thread -1229243472 get a data:4 from pos5 Thread -1218749520 put a data:5 to pos5 [Thread -1229243472 (LWP 21731) exited] [Thread -1208259664 (LWP 21729) exited] Thread -1218749520 put a data:6 to pos6 [New Thread -1239733328 (LWP 21732)] Thread -1218749520 put a data:7 to pos7 [Thread -1218749520 (LWP 21730) exited] Thread -1239733328 get a data:7 from pos7 Thread -1239733328 get a data:6 from pos6 Thread -1239733328 get a data:5 from pos5 Thread -1239733328 get a data:0 from pos4 Thread -1239733328 get a data:3 from pos3 Thread -1239733328 get a data:2 from pos2 Thread -1239733328 get a data:1 from pos1 Thread -1239733328 get a data:0 from pos0 [Thread -1239733328 (LWP 21732) exited] Program exited normally.