Linux IPC实践(6) --System V消息队列(3)

消息队列综合案例

消息队列实现回射客户/服务器


server进程接收时, 指定msgtyp为0, 从队首不断接收消息

server进程发送时, 将mtype指定为接收到的client进程的pid

client进程发送的时候, mtype指定为自己进程的pid

client进程接收时, 需要将msgtyp指定为自己进程的pid, 只接收消息类型为自己pid的消息;

// client/server进程接收/发送的数据结构
const int MSGMAX = 8192;
struct msgBuf
{
long mtype;         //保存客户进程的pid(需要将pid强制转换成为long)
char mtext[MSGMAX]; //保存客户进程真实发送的数据
};

//server.cpp
void echoServer(int msgid)
{
struct msgBuf buf;
int nrcv;
while (true)
{
bzero(&buf, sizeof(buf));
if ((nrcv = msgrcv(msgid, &buf, sizeof(buf.mtext), 0, 0)) == -1)
err_exit("msgrcv error");
cout << "recv: " << buf.mtext;
if (msgsnd(msgid, &buf, strlen(buf.mtext), 0) == -1)
err_exit("msgsnd error");
}
}

int main()
{
key_t key = ftok("/tmp/echoSeed", 0x1234);
int msgid = msgget(key, IPC_CREAT|0666);
if (msgid == -1)
err_exit("msgget error");

echoServer(msgid);
}

//client.cpp
void echoServer(int msgid)
{
struct msgBuf buf;
int nrcv;
while (true)
{
bzero(&buf, sizeof(buf));
if ((nrcv = msgrcv(msgid, &buf, sizeof(buf.mtext), 0, 0)) == -1)
err_exit("msgrcv error");
cout << "recv: " << buf.mtext;
if (msgsnd(msgid, &buf, strlen(buf.mtext), 0) == -1)
err_exit("msgsnd error");
}
}

int main()
{
key_t key = ftok("/tmp/echoSeed", 0x1234);
int msgid = msgget(key, IPC_CREAT|0666);
if (msgid == -1)
err_exit("msgget error");

echoServer(msgid);
}

附-ftok用法

#include <sys/types.h>
#include <sys/ipc.h>
key_t ftok(const char *pathname, int proj_id);

描述信息:

The ftok() function uses the identity(象征) of the file named by the given pathname (which must refer

to an existing, accessible file[必须是一个已经存在,并且可访问的文件]) and the least significant(有效的) 8 bits[有效的最低8位] of proj_id (which must be nonzero) to generate a key_t type System V IPC key, suitable

for use with msgget(2), semget(2), or shmget(2). The resulting value is the same for all pathnames that name the same file, when the same value of proj_id

is used(如果文件名与proj_id的有效位全都相同的话, 则生成的key一定也是相同的). The value returned should be different when

the (simultaneously existing) files or the project IDs differ.

RETURN VALUE On success, the generated key_t value is returned. On failure -1 is returned,

with errno indicating the error as for the stat(2) system call.