使用waitpid在后台运行进程？

Question

如果在命令末尾找到"&",我试图模仿后台运行进程的bash功能.我有以下功能......我不认为它正在做我想做的事情

int execute(char* args[],int background,int *cstatus){
    pid_t   child;
    pid_t   ch;                         /*Pid of child returned by wait*/
    if ((child = fork()) == 0){                 /*Child Process*/
        execvp(args[0],args);       
        fprintf(stderr, "RSI: %s: command not found\n",args[0]); /*If execvp failes*/
        exit(1);

    }else{          /*Parent process*/
        if (child== (pid_t)(-1)) {
            fprintf(stderr,"Fork failed\n"); exit(1);
        }else{
            if (background==0){             /*If not running in background..wait for process to finish*/
                ch = wait(cstatus);
            }else{
                printf("%ld Started\n",(long)getpid());
        /*  printf("Parent: Child %ld exited with status = %ld\n", (long) ch, (long)cstatus);
    */  }}
    }
return 0;
}
int wait_and_poll(int *cstatus){
    pid_t status;
    status = waitpid(-1,cstatus,WNOHANG);
    if (status>0){
        fprintf(stdout,"%ld Terminated.\n",(long) status);
    }
return 0;
}

如果我只是运行"ls -l"它按预期工作..但如果我想在后台运行ls ..并让程序继续接受新命令我调用函数,后台标志设置为1,我希望它在后台运行该进程,告诉我它已创建进程..然后提示接受下一个命令.

Answer 1

我不认为waitpid(-1, &cstatus, WNOHANG);你认为它做了什么.您需要检查其返回值.如果是> 0,那就是退出的子进程的PID.如果是0或者-1,没有子进程改变了状态.

您可以waitpid(-1, &cstatus, WNOHANG);在运行每个命令之前和/或之后调用.在循环中调用它以捕获多个子出口.

您还可以处理SIGCHILD.子进程退出后,您的进程将立即收到此信号,如果您想立即报告子进程终止,则无需等待用户输入.