c - 命名管道，使用 Fork()

Question

我遇到了一个很大的问题。因此，对于我的作业，我必须使用命名管道(FIFO)并使用 Fork()。我有三个程序，lab6(这是我的主/父/打印答案)，然后我有我的生命支持(这是一个 child )，然后我有我的导航(这也是一个 child )。两个 child 必须写信给 parent ，然后 parent 阅读并打印出来。确实很难解释答案应该如何。它很复杂，但我的数学是正确的，只有当我尝试将此文件移动到单独的 FIFO 文件中时才遇到问题。我收到段错误错误。所以我的问题是我做错了什么？我正在尝试将这段代码转换为 FIFO。附注不用担心任何时间或种子生成器或类似的东西。我只需要导航来计算其部分并将其发送给父级，生命支持也是如此，但我似乎无法让 FIFO 工作。

主文件-

  #include<unistd.h>
#include<stdio.h>
 #include<string.h>
 #include<stdlib.h>
 #include<sys/stat.h>
  #include<linux/stat.h>

 #define FIFO_FILE "MYFIFO"         //default is current directory


 void getTime();
 void writeToMain( char *, int );
 void lifeSupport();
  void navigation();
 int generate(int);
  void countdown( int );

 //Global Variables
  const int MAX_LINE = 80;
  int ret, myPipes[2];
   char *message;

 int time_;
  char myClock[25];

 //Pipe variables
  int totalTime = 0;
  char toSend[120];



int main(void){

    FILE *fpoint;
    char readbuffer[80];
    int again = 1;


    mknod(FIFO_FILE, S_IFIFO | 0666, 0);

    while(again){

    fpoint = fopen(FIFO_FILE, "r");
    fgets(readbuffer, 80, fpoint);
    printf("recevived string: %s\n, readbuffer");
    fclose(fpoint);
    if(strcmp(readbuffer, "stop") == 0 ) again = 0;

    return(0);

            }


              if( ret == 0 ){
            if(fork() == 0){

                    while (repeat){

                            totalTime = 0;
                             getTime();
                            lifeSupport();
                            navigation();

                            getTime();
                            sprintf(toSend, "[ %s ] \tSleep \t\t[ %d  second(s) ]\n", myClock, 30 - totalTime);
                            write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );

                            sleep(30 - totalTime);
                    }
            }

            else{

                    while(again){
                    read( myPipes[PipeStdIn], buffer, MAX_LINE);
                    again = strcmp(buffer, "Stop");


                    if (again == 0) ;
                            else
                                printf("%s \n", buffer);
                     }

            }
         }//exit main

child (生命支持)-

       #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    #include<unistd.h>
    #include<sys/stat.h>
    #include<linux/stat.h>
    #define FIFO_FILE "MYFIFO"



    void getTime();
    void writeToMain( char *, int );
    void lifeSupport();
    void navigation();
    int generate(int);
    void countdown( int );

    void lifeSupport(){
            getTime();
            message = "Beginning life support systems \t";
            sprintf(toSend, "[ %s ] %s ", myClock, message);
            write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
            sleep(1);
            totalTime ++;

            getTime();
            time_ = generate(5);
            message = "Adjusting breathing gas levels";
            sprintf(toSend, "[ %s ] %s  \t[ %d Second(s) ]", myClock, message, time_);
            write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
            sleep(time_);
      totalTime += time_;

             getTime();
            time_ = generate(3);
            message = "Adjusting environment";
            sprintf(toSend, "[ %s ] %s  \t\t[ %d Second(s) ]", myClock, message, time_);
            write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
            sleep(time_);
            totalTime += time_;

            getTime();
            message = "Done. Life support adjusted. \t[ 1 Second(s) ]";
            sprintf(toSend, "[ %s ] %s ", myClock, message);
            write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
            sleep(1);
            totalTime ++;

             getTime();
            message = "\t\tExecution time";
            sprintf(toSend, "%s [ %d Second(s) ]\n", message, (totalTime - 1));
    write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
    sleep(1);
    totalTime ++;


            FILE *fpoint;
            int again =1;
            char strIn[80] = "Use message from command line";

            if(argc !=2){
         printf("USAGE: NamedPipeClient[string]\n");
                    exit(1);
                    }

            while(again == 1){

            if((fpoint = fopen (FIFO_FILE, "w")) == NULL){
                    perror("fopen");
                    exit(1);

            if((fpoint = fopen(FIFO_FILE, "w")) == NULL){
                    perror("fopen");
                    exit(1);
                            }
                    }
            }

和最后一个 child (导航。记住两个 child 都会写信给 parent )-

       #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    #include<unistd.h>
    #include<sys/stat.h>
    #include<linux/stat.h>
    #define FIFO_FILE "MYFIFO"


    void getTime();
    void writeToMain( char *, int );
    void lifeSupport();
    void navigation();
    int generate(int);
    void countdown( int );

    void navigation(){
    getTime();
    message = "Beginning navigation systems";
    sprintf(toSend, "[ %s ] %s \t[ 1 Second(s) ]", myClock, message);
    write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
    sleep(1);
    totalTime ++;

    getTime();
    time_ = generate(6);
    message = "Adjusting navigation systems";
    sprintf(toSend, "[ %s ] %s  \t[ %d Second(s) ]", myClock, message, time_);
    write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
    sleep(time_);
    totalTime += time_;
           getTime();
    message = "Done. Navigation systems adjusted \t[ 1 Second(s) ]";
    sprintf(toSend, "[ %s ] %s ", myClock, message);
    write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
    sleep(1);
    totalTime ++;

    message = "\t\tExecution time";
    sprintf(toSend, "%s  [ %d Second(s) ]", message, (totalTime - 2));
    write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
    sleep(1);
    totalTime += 2;

    getTime();
    message = "\tTotal time";
    sprintf(toSend, "[ %s ] %s \t[ %d Second(s) ]",  myClock, message, totalTime);
    write( myPipes[PipeStdOut], toSend, strlen(toSend) + 1 );
    sleep(1);



            while(again == 1){

            if((fpoint = fopen (FIFO_FILE, "w")) == NULL){
                    perror("fopen");
                    exit(1);
            }

            if((fpoint = fopen(FIFO_FILE, "w")) == NULL){
                 perror("fopen");
                    exit(1);
            }
    }
            fputs(strIn,fpoint);
            fclose(fpoint);

    return(0);
    }

我知道这很多，并且非常感谢任何帮助。如果这太多了，我会尊重规则并删除除此之外的问题，我认为这将是一个不错的挑战。哈哈提前致谢!

Answer 1

您似乎试图尽可能地向我们混淆您的问题。您的程序示例不是最小的 - 它归结为(主要)

int main (void){

   mknod(FIFO_FILE, S_IFIFO | 0666, 0);

   while(again){

      fpoint = fopen(FIFO_FILE, "r");
      fgets(readbuffer, 80, fpoint);
      printf("recevived string: %s\n, readbuffer");
      fclose(fpoint);

      // All the fork() stuff follows here
      ....
   }

您创建 FIFO，打开它并从中读取(不检查您是否确实得到了某些内容)。当您的 child 处理实际上尚未开始的事情时，您希望谁在其中放入一些东西？

因为您没有检查 fgets() 的返回值，所以您将在未初始化的缓冲区 (readbuffer) 上工作，并且这里会发生严重破坏。

即使如果你有一些外部的东西神奇地写入了 FIFO，你需要检查 fgets() 的返回值，尤其是在多进程环境 - 当您读取时，您不能假设其他进程已经写了一些东西。