如何编写一个程序来告诉我的其他程序什么时候结束？

Question

如何编写一个程序来告诉我的其他程序什么时候结束？

Answer 1

在没有自己生成的程序上执行waitpid()或waitid()的唯一方法是通过ptrace来成为它的父级.

下面是一个如何在posix操作系统上使用ptrace临时成为另一个进程父进程的示例,然后等待该程序退出.作为副作用,您还可以获得退出代码以及导致该程序退出的信号:

#include <sys/ptrace.h>
#include <errno.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>

int main(int argc, char** argv) {

    int pid = atoi(argv[1]);
    int status;
    siginfo_t si;

    switch (ptrace(PTRACE_ATTACH, pid, NULL)) {
        case 0:
            break;
        case -ESRCH:
        case -EPERM:
            return 0;
        default:
            fprintf(stderr, "Failed to attach child\n");
            return 1;
    }
    if (pid != wait(&status)) {
        fprintf(stderr, "wrong wait signal\n");
        return 1;
    }
    if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP))  {
        /* The pid might not be running */
        if (!kill(pid, 0)) {
            fprintf(stderr, "SIGSTOP didn't stop child\n");
            return 1;
        } else {
            return 0;
        }
    }
    if (ptrace(PTRACE_CONT, pid, 0, 0)) {
        fprintf(stderr, "Failed to restart child\n");
        return 1;
    }

    while (1) {
        if (waitid(P_PID, pid, &si, WSTOPPED | WEXITED)) {
            // an error occurred.
            if (errno == ECHILD)
                return 0;
            return 1;
        }
        errno = 0;

        if (si.si_code & (CLD_STOPPED | CLD_TRAPPED)) {
            /* If the child gets stopped, we have to PTRACE_CONT it
             * this will happen when the child has a child that exits.
             **/
            if (ptrace(PTRACE_CONT, pid, 1, si.si_status)) {
                if (errno == ENOSYS) {
                    /* Wow, we're stuffed. Stop and return */
                    return 0;
                }
            }
            continue;
        }

        if (si.si_code & (CLD_EXITED | CLD_KILLED | CLD_DUMPED)) {
            return si.si_status;
        }
        // Fall through to exiting.
        return 1;
    }
}