Linux 进程间通讯详解七

上图的一台主机服务器架构的重大缺陷是容易死锁
因为客户端，服务器都往同一消息队列中发送接收消息,假设消息队列已经满了，此时客户端无法向队列中发送消息，阻塞了，
而服务器接收完一条消息后，想向消息队列发送消息，由于消息队列已经满了，也阻塞了，此时就会死锁。

改进型的一台主机服务器架构
建立两个消息队列，一个用于客户端写入服务器接收，一个用于服务器发送客户端接收，这样则永远不会出现死锁

//本机客户端
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <pthread.h>

struct msgbuf
{
long mtype; /* message type, must be > 0 */
char mtext[1024]; /* message data */
};

int get_msqid(const char *pathname)
{
if (pathname == NULL)
{
printf("get_msqid() params not correct !\n");
return -1;
}
char *pvalue1 = getenv(pathname);
if (pvalue1 == NULL)
{
printf("getenv() failed !\n");
return -1;
}
key_t sendkey = ftok(pvalue1, 1);
if (sendkey == -1)
{
perror("ftok() err");
return -1;
}
int msqid = msgget(sendkey, 0666 | IPC_CREAT | IPC_EXCL);
if (msqid == -1)
{
if (errno == EEXIST)
{
printf("该消息队列已经存在！\n");
msqid = msgget(sendkey, 0666);
} else
{
perror("msgget() err");
return -1;
}
}
return msqid;
}

void * start_routine(void * arg)
{
//客户端发送消息队列
int msqid = get_msqid("SENDFILE");
struct msgbuf buf;
memset(&buf, 0, sizeof(buf));
buf.mtype = 1;
//数据的前4个字节存放当前进程的pid
*((int *) buf.mtext) = getpid();
while (fgets(buf.mtext + 4, 1020, stdin) != NULL)
{
//发送消息队列
if (msgsnd(msqid, &buf, sizeof(int) + strlen(buf.mtext + 4), 0) == -1)
{
perror("msgsnd() err");
return NULL;
}
memset(buf.mtext + 4, 0, 1020);
}
return NULL;
}

int main(int arg, char * args[])
{
//开启多线程
pthread_t thr1;
//设置分离线程
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
if (pthread_create(&thr1, &attr, start_routine, NULL) != 0)
{
printf("pthread_create() failed !\n");
return -1;
}
//客户端接收消息队列
int msqid = get_msqid("RECVFILE");
//recv
int rc = 0;
struct msgbuf buf;
while (1)
{
memset(&buf, 0, sizeof(buf));
rc = msgrcv(msqid, &buf, 1024, getpid(), 0);
if (rc == -1)
{
perror("msgrcv() err");
break;
}
printf("服务器有消息到来，消息长度是%d\n",rc);
fputs(buf.mtext, stdout);
}
return 0;
}

//本机服务器
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

struct msgbuf
{
long mtype; /* message type, must be > 0 */
char mtext[1024]; /* message data */
};

int get_msqid(const char *pathname)
{
if (pathname == NULL)
{
printf("get_msqid() params not correct !\n");
return -1;
}
char *pvalue1 = getenv(pathname);
if (pvalue1 == NULL)
{
printf("getenv() failed !\n");
return -1;
}
key_t sendkey = ftok(pvalue1, 1);
if (sendkey == -1)
{
perror("ftok() err");
return -1;
}
int msqid = msgget(sendkey, 0666 | IPC_CREAT | IPC_EXCL);
if (msqid == -1)
{
if (errno == EEXIST)
{
printf("该消息队列已经存在！\n");
msqid = msgget(sendkey, 0666);
} else
{
perror("msgget() err");
return -1;
}
}
return msqid;
}

int main(int arg, char * args[])
{
/*客户端的发送消息队列，是服务器的接收消息队列*/
int send_msqid = get_msqid("RECVFILE");
if (send_msqid == -1)
return -1;
int recv_msqid = get_msqid("SENDFILE");
if (recv_msqid == -1)
return -1;
//接收消息再发送
int rc = 0;
struct msgbuf recvbuf;
struct msgbuf sendbuf;
int pid=0;
while (1)
{
memset(&recvbuf,0,sizeof(struct msgbuf));
memset(&sendbuf,0,sizeof(struct msgbuf));
rc = msgrcv(recv_msqid, &recvbuf, 1024, 1, 0);
if(rc==-1)
{
perror("msgrcv() err");
return -1;
}
printf("客户端有数据到来！数据的长度是%d\n",rc);
//解析数据
pid=*((int *)recvbuf.mtext);
sendbuf.mtype=pid;
strcpy(sendbuf.mtext,recvbuf.mtext+4);
fputs(sendbuf.mtext,stdout);
//发送
if(msgsnd(send_msqid,&sendbuf,rc-4,0)==-1)
{
perror("msgsnd() err");
return -1;
}
}
return 0;
}

.SUFFIXES:.c .o
CC=gcc
SRCS1=test01.c
OBJS1=$(SRCS1:.c=.o)
EXEC1=clt
SRCS2=tec02.c
OBJS2=$(SRCS2:.c=.o)
EXEC2=ser

start:$(OBJS1) $(OBJS2)
$(CC) -o $(EXEC1) $(OBJS1) -lpthread
$(CC) -o $(EXEC2) $(OBJS2)
@echo "-------OK---------"
.c.o:
$(CC) -Wall -g -o $@ -c $<
clean:
rm -f $(OBJS1)
rm -f $(OBJS2)
rm -f $(EXEC1)
rm -f $(EXEC2)