Question

更新：当我设置act.sa_flags = SA_RESTART时，程序会停止分段错误，但它会导致程序被卡住＆＃34;在该函数中，因为它没有继续我的程序中的逻辑。冒号表示新命令行输入的开始。理想的输出如下：

 : ls
 smallsh.c small
 : sleep 5 & //background process
 : ls > junk
 background pid # is complete terminated by signal $ //when background sleep finishes
 :

但是我现在得到以下内容：

 : ls
 smallsh.c small
 : sleep 5 & //background process
 : ls > junk
 background pid # is complete terminated by signal $ 
 //cursor is pointing here but no colon appears, i can still write commands
 //and they will work but function believers they are all background processes

上一篇：我尝试使用C语言中的背景和前台进程编写一个简单的shell。为了创建后台进程，用户必须输入一个＆＃34;＆amp;＆＃34;在他们的命令结束时，例如＆＃34;睡眠3＆amp;＆＃34;将是一个后台进程。在我进入＆＃34;睡眠3＆amp;＆＃34;该过程成功运行，但在完成调用sig处理函数时，将打印一个语句（表明后台进程已结束），然后程序seg出错。以下是输出结果的示例：

：睡3＆amp; 背景pid是22688 ：后台pid 0完成：由信号0终止分段错误：11

当我尝试运行后台进程并且我不确定原因时，会调用我的信号处理程序。当我设置sigaction以使用SIGINT时，程序不会出错。有什么想法吗？我在这里看到了类似的帖子（SIGCHLD causing segmentation fault, not going into handler）但它并没有帮助我。

pid_t spawnPID = -5
int exitMethod; 
int exitStatus = 0;
char bgPID[10];

//Set up signal handler
struct sigaction act;
act.sa_handler = sig_handler;
act.sa_flags = 0;
sigfillset(&(act.sa_mask));

fflush(stdout);


if (bg == 1)
{
 sigaction(SIGCHLD, &act, NULL);
}


switch(spawnPID)
{
    case -1:
    {
        //There was an error forking
        printf("Error forking\n");
        fflush(stdout);
        exitStatus = 1; 
    }
    case 0:   //Child process
    {

        //Check for input/output redirection
        if (numArgs > 1)
        {

            if (!(strncmp(arguments[1], ">", 1)))
            {

                exitStatus = outputRedirect(arguments,numArgs);
            }
            else if (!(strncmp(arguments[1], "<", 1)) || (! 
            (strncmp(arguments[0], "cat", 1))))
            {
                exitStatus = inputRedirect(arguments,numArgs);
            }
            else
            {

            arguments[numArgs] = NULL; //set last value in the array to NULL 


            if (execvp(arguments[0],arguments) == -1)
            {
                printf("Command or file not recognized\n"); //won't run unless there is an error
                fflush(stdout);
                exitStatus = 1;
            }
        }
    }
        else //run other command
        {

            if (execvp(arguments[0],arguments) == -1)
            {
                printf("%s: No such command, file or directory\n", arguments[0]); //won't run unless there is an error
                fflush(stdout);
                exitStatus = 1;
            }

        }
        break;

    }
//Following code is in the parent case of the switch statement

default:



if (bg == 0)  //waitpid is only called in a parent in a foreground process
{
  pid_t exitpid = waitpid(spawnPID,&exitMethod,0); //Wait for one of the     
  //children to be completed
{


 if (WIFEXITED(exitMethod))
 {
   int exitStatus = WEXITSTATUS(exitMethod);
 }


 //Sig Handler function

void sig_handler (int signo)
{
  int status;
  pid_t childPid;
  char bgMessage[50];
  char bgPID[10];
  char exitStatus[10];

  childPid = waitpid(-1, &status, 0);


  sprintf(bgPID,"%d",childPid);
  sprintf(exitStatus,"%d",WEXITSTATUS(status));
  strcat(bgMessage,"background pid ");
  strcat(bgMessage,bgPID);
  strcat(bgMessage," is done: terminated by signal " );
  strcat(bgMessage,exitStatus);
  strcat(bgMessage,"\n");

  // Write out the message
  write(1, bgMessage, sizeof(bgMessage));
}

在简单的shell程序

0 个答案: