C Linux (Ubuntu) - msgsnd()和msgrcv() errno 22 (EINVAL)

Question

我正在尝试IPC (消息传递)一段时间，但我无法解决这个问题。msgget()的errno 22 (EINVAL)似乎是无效的消息队列标识符、非正消息类型或无效消息大小。现在，对msgrcv()的errno 22是msgqid无效的，或者msgsz小于0，因此这似乎表明我的队列ID是错误的，因为无效的msqueue id重叠在两个错误解释中。

我应该注意我的msgget()调用返回0作为队列ID，这个‘应该’很好，因为文档说任何非负的返回值都是有效的。有什么想法吗？

在将计数器调整为一个计数器后，运行输出(不想粘贴100条错误消息)：

msqID = 0，sendMessage.msgText = Hola!：0，sendMessage.msgType = 1，MSG_SIZE = 256 roh，在父发送中：：无效参数子msgrcv()：msqID = 0，rcvMessage.msgText =，rcvMesage.msgType = 1，MSG_SIZE = 256 roh，在子rcv：：无效参数中

这在第31行(父进程中的第一个msgsnd() )和第60行(子进程中的第一个msgrcv() )上失败。

#include <errno.h>
#include <sys/msg.h>
#include <sys/ipc.h>
#include <time.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <math.h>
const int MAX_TEXT_SIZE = 255;
const int COUNTER = 99;
int main(){
  srand(time(NULL));
  int childPID, key = rand(), msgSendRslt, msgRecvRslt, msqID;
  long int type  = 1;
  struct msg {long msgType; char msgText[MAX_TEXT_SIZE];};
  const int MSG_SIZE = sizeof(struct msg)-sizeof(long int);
    if(msqID = msgget(key, IPC_CREAT | 0666) == -1){
      perror("\nRuh roh: ");
      exit(1);
    }
    if((childPID = fork()) > 0){
      struct msg sendMessage, rcvMessage;
      sendMessage.msgType = type;
      char *sendMsg = malloc(MAX_TEXT_SIZE);
      for(int i = 0; i < 100; i++){
        sprintf(sendMsg, "Hola!: %d", i);
        strcpy(sendMessage.msgText, sendMsg);
        printf("\nmsqID = %d, sendMessage.msgText = %s, sendMessage.msgType = %ld, MSG_SIZE = %d", msqID, sendMessage.msgText, sendMessage.msgType, MSG_SIZE);
        printf("\n");
        if(msgsnd(msqID, &sendMsg, MSG_SIZE, IPC_NOWAIT) != -1){
          printf("\nFrom parent, sent msg %d", i);
          if(msgrcv(msqID, &rcvMessage, MSG_SIZE, rcvMessage.msgType, IPC_NOWAIT) != -1){;
            printf("\nIn the parent, received from child: %s", rcvMessage.msgText);
          }
          else
            perror("\nRuh roh, in parent rcv: ");
        }
        else
          perror("\nRuh roh, in parent send: ");
          printf("\nerrno: %d", errno);
      }
      strcpy(sendMessage.msgText, "Over and out!");
      if(msgsnd(msqID, &sendMsg, MSG_SIZE, 0) == -1)
        perror("\nRuh roh, in parent send at end: ");
    }
  else if (childPID == 0){ //child
    int count = 0;
    int test = ceil(3.8);
    char *countS = malloc(ceil(log(COUNTER)/log(10)));
    struct msg rcvMessage, sendMessage;
    strcpy(rcvMessage.msgText, "");
    sendMessage.msgType = type;
    rcvMessage.msgType = type;
    while(strcmp(rcvMessage.msgText, "Over and out!") != 0){
      sprintf(countS, "%d", count);
      strcat(strcpy(sendMessage.msgText, "10-4 good buddy!: "), countS);
      printf("\nchild msgrcv(): msqID = %d, rcvMessage.msgText = %s, rcvMesage.msgType = %ld, MSG_SIZE = %d", msqID, rcvMessage.msgText, rcvMessage.msgType, MSG_SIZE);
      printf("\n");
      if(msgrcv(msqID, &rcvMessage, MSG_SIZE, rcvMessage.msgType, IPC_NOWAIT) != -1){
        printf("\nIn the child, received from the parent: %s", rcvMessage.msgText);
        if(msgsnd(msqID, &sendMessage, MSG_SIZE, IPC_NOWAIT) == -1)
          perror("\nRuh roh, in child send: ");
          exit(1);
      }
      else
        perror("Ruh roh, in child rcv: ");
        printf("\nChild error: %d", errno);
        exit(1);
    }
  }
  else{
    perror("\nRuh roh, fork() problem: ");
    printf("\n");
    exit(1);
  }
}

Answer 1

我盯着你的代码看了很长一段时间才能发现问题。

if(msqID = msgget(key, IPC_CREAT | 0666) == -1)

括号在错误的地方！该代码有效地将msgget(key, IPC_CREAT | 0666) == -1分配给msqID。也就是说，msqID是条件的结果，并解释了为什么msqID总是0。

正确的代码应该如下所示。注意括号的位置。

if((msqID = msgget(key, IPC_CREAT | 0666)) == -1)