我正在模拟一个udp服务器，它通过udp客户端接收多个请求消息。我需要在这个udp服务器示例代码中生成2个线程。线程1将在它们到达时收到所有udp请求，并通过消息队列将其发送到线程2进行处理。
线程1（SndMq）能够通过udp接收请求消息，并且能够使用结构将其放入消息队列中。但问题是线程2（RcvMq）无法读取消息队列中的单个消息。请提出任何解决方案。
错误部分（线程2功能）：
void* RcvMq(void*) {
time_t t2;
time(&t2);
msgst *msg = new msgst;
int mqid = msgget((key_t)12345, 0666 | IPC_CREAT);
if (mqid == -1) {
printf("thread 2: msgget failed with error: %d\n", errno);
exit(EXIT_FAILURE);
}
else
printf("\nthread 2: got MQ id: %d\n", mqid);
long receive_m_type = 123;
printf("thread 2: going to enter while(1) loop\n");
while(1) {
printf("\nthread 2: inside while(1) loop, going to msgrcv()\n");
if ( msgrcv(mqid, (void *)&msg, BUFSIZE, receive_m_type, 0) < 0 ) {
//printf("\nthread 2: msgrcv failed with error: [%s]\n", strerror(errno));
printf("\nthread 2: msgrcv failed with error\n");
exit(EXIT_FAILURE);
}
else {
printf("thread 2: going to ctime()\n");
printf("\nthread 2: DeQueued at: %s\n", ctime(&t2));
}
printf("\nthread 2: going to print struct's buffer\n");
printf("thread 2: Message received at MQ rcv is: %s \n", msg->buffer);
}
}
udp服务器模拟器的代码
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <time.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/msg.h>
#include<pthread.h>
#define PORT 5000
#define BUFSIZE 2048
pthread_t sndtid;
pthread_t rcvtid;
typedef struct msgst {
long int mtype;
char buffer[BUFSIZE];
}msgst;
void* SndMq(void*) {
time_t t1;
time(&t1);
struct sockaddr_in myaddr; /* our address */
struct sockaddr_in remaddr; /* remote address */
socklen_t addrlen = sizeof(remaddr); /* length of addresses */
int recvlen; /* # bytes received */
int fd; /* our socket */
int rc, on=1;
char buf[BUFSIZE]; /* receive buffer */
size_t buflen;
/* create a UDP socket: socket, setsockopt, bind */
if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
perror("cannot create socket\n");
return 0;
}
if((rc = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (char *)&on, sizeof(on))) < 0) {
perror("thread 1: UDP Server setsockopt() - ERROR");
close(fd);
exit(-1);
}
/* bind the socket to any valid IP address and a specific port */
memset((char *)&myaddr, 0, sizeof(myaddr));
myaddr.sin_family = AF_INET;
myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
//myaddr.sin_port = htons(SERVICE_PORT);
myaddr.sin_port = htons(PORT);
if ( bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr) ) < 0) {
perror("bind failed");
return 0;
}
printf("\nthread 1: Server waiting on port %d\n", PORT);
//MsgQ implementation:
int mqid = msgget((key_t)12345, 0666 | IPC_CREAT);
if(mqid == -1) {
printf("thread 1: msgget() failed, errno: %d\n",errno );
}
else
printf("thread 1: created MQ id: %d\n", mqid);
/* now loop, receiving data and printing what we received */
for (;;) {
//rcv from udp client
recvlen = recvfrom(fd, buf, BUFSIZE, 0, (struct sockaddr *)&remaddr, &addrlen);
printf("\nthread 1: received %d bytes\n", recvlen);
if (recvlen > 0) {
buf[recvlen] = 0;
printf("thread 1: received message from UDP client: %s\n", buf);
}
//send received msg via MsgQ
msgst *msgptr = new msgst;
msgptr->mtype = 123;
strcpy(msgptr->buffer, buf);
//msgptr->buffer=buf;
//memcpy(msgptr->buffer, buf, BUFSIZE);
buflen = strlen(msgptr->buffer);
if (msgsnd(mqid, (void *)&msgptr, buflen, IPC_NOWAIT) == -1) {
printf("thread 1: msgsnd failed\n");
exit(EXIT_FAILURE);
}
printf("thread 1: added Req to MsgQ at: %s\n", ctime(&t1));
}/* never exits */
}
void* RcvMq(void*) {
time_t t2;
time(&t2);
msgst *msg = new msgst;
int mqid = msgget((key_t)12345, 0666 | IPC_CREAT);
if (mqid == -1) {
printf("thread 2: msgget failed with error: %d\n", errno);
exit(EXIT_FAILURE);
}
else
printf("\nthread 2: got MQ id: %d\n", mqid);
long receive_m_type = 123;
printf("thread 2: going to enter while(1) loop\n");
while(1) {
printf("\nthread 2: inside while(1) loop, going to msgrcv()\n");
if ( msgrcv(mqid, (void *)&msg, BUFSIZE, receive_m_type, 0) < 0 ) {
//printf("\nthread 2: msgrcv failed with error: [%s]\n", strerror(errno));
printf("\nthread 2: msgrcv failed with error\n");
exit(EXIT_FAILURE);
}
else {
printf("thread 2: going to ctime()\n");
printf("\nthread 2: DeQueued at: %s\n", ctime(&t2));
}
printf("\nthread 2: going to print struct's buffer\n");
printf("thread 2: Message received at MQ rcv is: %s \n", msg->buffer);
}
}
int main() {
int rtn=0;
rtn = pthread_create(&(sndtid), NULL, &SndMq, NULL);
if (rtn != 0)
printf("\ncan't create thread SndMq, error:[%s]", strerror(rtn));
else
printf("\n\ncreated SndMq thread\n");
rtn = pthread_create(&(rcvtid), NULL, &RcvMq, NULL);
if (rtn != 0)
printf("\ncan't create thread RcvMq :[%s]", strerror(rtn));
else
printf("created RcvMq thread\n");
printf("main(): All threads spawned successfully, now waiting for threads to end...\n");
pthread_join(sndtid, NULL);
pthread_join(rcvtid, NULL);
printf("\nThreads ended, main() exiting now...\n");
return 0;
}
created SndMq thread
created RcvMq thread
main(): All threads spawned successfully, now waiting for threads to end...
thread 2: got MQ id: 6422528
thread 2: going to enter while(1) loop
thread 2: inside while(1) loop, going to msgrcv()
thread 1: Server waiting on port 5000
thread 1: created MQ id: 6422528
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>1</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>2</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>3</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>4</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>5</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>6</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>7</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>8</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>9</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
thread 1: received 1500 bytes
thread 1: received message from UDP client: <TransactionId>10</TransactionId>
thread 1: added Req to MsgQ at: Sat Apr 5 18:16:45 2014
答案 0 :(得分：2)
（1）您的主要问题是C错误。您正在将ptr的地址（ptr传递给ptr）而不是指针。
msgst *msgptr = new msgst;
//...
if (msgsnd(mqid, (void *)&msgptr, buflen, IPC_NOWAIT) == -1)
应该是
if (msgsnd(mqid, (void *) msgptr, buflen, IPC_NOWAIT) == -1)
因此，你正在编写任何随机垃圾和＆amp; msgptr，因为你正在编写msgtype 123，然后尝试读取msgtype 123（但写垃圾）你永远不会（或很少！）找到该消息类型
您在邮件接收方面犯了同样的错误：
msgst *msg = new msgst;
//.......
if ( msgrcv(mqid, (void *)&msg, BUFSIZE, receive_m_type, 0) < 0 )
（2）你可能还没有达到目的但你有一个内存泄漏，因为你new缓冲但从不delete。无论如何，你真的不需要动态内存分配。将缓冲区分配到堆栈上会更容易，因为它只会被msgsnd复制，然后你就完成了它。这也可以消除您遇到的问题（1）。
（3）您将在msgsnd上遇到IPC_NOWAIT问题。在消费者处理之前，很容易在生产者端填充队列。至少你应该检查EAGAIN并在写入失败时采取适当的措施。
答案 1 :(得分：1)
可能与提出的问题无关。
但是在SndMq() recvfrom()如果BUFSIZE收到buf个字节，则代码会在此处写出 buf[recvlen] = 0;
的界限：
recvlen = recvfrom(fd, buf, BUFSIZE, 0, (struct sockaddr *)&remaddr, &addrlen);
<强>更新
要解决此问题，请更改此行
recvlen = recvfrom(fd, buf, BUFSIZE - 1, 0, (struct sockaddr *)&remaddr, &addrlen);
成为
{{1}}