[C++知识库]线程间通信的两种方式：消息队列、共享内存

一、消息队列

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>

#include <unistd.h>
#include <string.h>
#include <strings.h>
#include <stdio.h>

#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/shm.h>
#include <semaphore.h> 
#include <pthread.h>

struct msgbuf{
	long mtype;
	char mtext[50];
};

void *routine1(void *arg)
{
	struct msgbuf buf;
	int msgid = (int)arg;
	int ret;
	
	while(1)
	{
		bzero(&buf,sizeof(buf));
		ret = msgrcv(msgid,&buf,sizeof(buf),30,0);
		if(ret == -1)
		{
			printf("msgrcv error!\n");
		}	
		
		printf("buf.mtext = %s",buf.mtext);
		
		sleep(1);	
	}
	
	pthread_exit(NULL);
}

void *routine2(void *arg)
{
	struct msgbuf buf;
	int msgid = (int)arg;
	int ret;
	
	while(1)
	{
		bzero(&buf,sizeof(buf));
		buf.mtype = 30;
		fgets(buf.mtext,sizeof(buf.mtext),stdin);
		
		msgsnd(msgid,&buf,strlen(buf.mtext),0);	
	}
}

int main()
{
	key_t key;
	int msgid;
	
	key = ftok(".",10);
	msgid = msgget(key,IPC_CREAT | 0666);
	
	pthread_t tid1,tid2;
	
	pthread_create(&tid1,NULL,routine1,(void *)msgid);
	pthread_create(&tid2,NULL,routine2,(void *)msgid);
	
	pause();
	
}

二、共享内存

共享内存中被映射的空间属于临界资源所以要上锁

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>

#include <unistd.h>
#include <string.h>
#include <strings.h>
#include <stdio.h>

#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/shm.h>
#include <semaphore.h> 
#include <pthread.h>


pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;

//负责写入数据到共享内存中
void *Jack_fun(void *arg)
{
	char *p = (char *)arg;
	while(1)
	{
		//每次写入数据之前都要上锁
		pthread_mutex_lock(&m);
		
		fgets(p,8192,stdin);
		
		//每次写完数据后，都要解锁
		pthread_mutex_unlock(&m);
		
		if(strncmp(p,"quit",4) == 0)
		{
			break;
		}
		
		usleep(100000);   //sleep(1)  等价于  usleep(1000000);
						 //为了先让Rose先上锁
	}
	
	pthread_exit(NULL);
}

//负责从共享内存中读取数据
void *Rose_fun(void *arg)
{
	usleep(50000); //0.05S  为了先让Jack先上锁！
	char *p = (char *)arg; 
	while(1)
	{
		//每次写入数据之前都要上锁
		pthread_mutex_lock(&m);
		
		printf("from shm:%s",p);
		
		//每次写完数据后，都要解锁
		pthread_mutex_unlock(&m);
		
		if(strncmp(p,"quit",4) == 0)
		{
			break;
		}
		
		usleep(130000); //为了让Jack先上锁！
	}
	
	pthread_exit(NULL);
}


int main()
{
	key_t key;
	int shmid;
	
	//1. 申请共享内存的key值
	key = ftok(".",10);
	
	//2. 申请共享内存ID
	shmid = shmget(key,8192,IPC_CREAT|0666);
	
	//3. 映射一片内存空间,NULL代表系统分配空间
	char *p = (char *)shmat(shmid,NULL,0);
	
	//4. 主线程产生两个子线程，两个子线程都是随机执行
	pthread_t Jack,Rose;
	pthread_create(&Jack,NULL,Jack_fun,(void *)p);
	pthread_create(&Rose,NULL,Rose_fun,(void *)p);
	
	pthread_join(Jack,NULL);
	pthread_join(Rose,NULL);
	
	return 0;
}