Question

我有一个程序使用popen()来打开和读取shell命令的输出。问题是，据我所知，没有简单的方法来获取正在运行的进程的PID，因此，如果它被卡住，你就无法杀死它。那么问题是，如何从使用popen打开的流程中检索PID？

Answer 1

我提出的解决方案（以及普遍共识）是创建一个允许我检索PID的新popen函数。由于我无法在SO上找到一个简单的例子，我希望发布我的实现，希望它能帮助其他人。欢迎提供反馈和替代解决方案。

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <signal.h>
#include <string.h>
#include <sys/wait.h>
#include <errno.h>
#include <string>
#include <sstream>

using namespace std;

#define READ   0
#define WRITE  1
FILE * popen2(string command, string type, int & pid)
{
    pid_t child_pid;
    int fd[2];
    pipe(fd);

    if((child_pid = fork()) == -1)
    {
        perror("fork");
        exit(1);
    }

    /* child process */
    if (child_pid == 0)
    {
        if (type == "r")
        {
            close(fd[READ]);    //Close the READ end of the pipe since the child's fd is write-only
            dup2(fd[WRITE], 1); //Redirect stdout to pipe
        }
        else
        {
            close(fd[WRITE]);    //Close the WRITE end of the pipe since the child's fd is read-only
            dup2(fd[READ], 0);   //Redirect stdin to pipe
        }

        setpgid(child_pid, child_pid); //Needed so negative PIDs can kill children of /bin/sh
        execl("/bin/sh", "/bin/sh", "-c", command.c_str(), NULL);
        exit(0);
    }
    else
    {
        if (type == "r")
        {
            close(fd[WRITE]); //Close the WRITE end of the pipe since parent's fd is read-only
        }
        else
        {
            close(fd[READ]); //Close the READ end of the pipe since parent's fd is write-only
        }
    }

    pid = child_pid;

    if (type == "r")
    {
        return fdopen(fd[READ], "r");
    }

    return fdopen(fd[WRITE], "w");
}

int pclose2(FILE * fp, pid_t pid)
{
    int stat;

    fclose(fp);
    while (waitpid(pid, &stat, 0) == -1)
    {
        if (errno != EINTR)
        {
            stat = -1;
            break;
        }
    }

    return stat;
}

int main()
{
    int pid;
    string command = "ping 8.8.8.8"; 
    FILE * fp = popen2(command, "r", pid);
    char command_out[100] = {0};
    stringstream output;

    //Using read() so that I have the option of using select() if I want non-blocking flow
    while (read(fileno(fp), command_out, sizeof(command_out)-1) != 0)
    {
        output << string(command_out);
        kill(-pid, 9);
        memset(&command_out, 0, sizeof(command_out));
    }

    string token;
    while (getline(output, token, '\n'))
        printf("OUT: %s\n", token.c_str());

    pclose2(fp, pid);

    return 0;
}

Answer 2

澄清

我尝试使用@Gillespie的答案定义的函数，但发现C / C ++程序中的pid与终端命令pgrep返回的函数不同，并查看输出ps -aux | grep myNameProc的C语言程序似乎再次被派生了。

我认为是因为execl("/bin/sh", "/bin/sh", "-c", command.c_str(), NULL);实际上等效于/bin/sh cmd string。因此，基本上，您的C（或C ++）程序的子进程正在创建一个执行/bin/sh yourRealProcess的新进程，其中yourRealProcess是指定的command字符串。

我解决了以下问题：execl(command.c_str(), command.c_str(), (char*)NULL);。但是，正如@Gillespie在前面的注释中所指定的那样，您将无法将参数传递给您的过程。

C实施

根据我的需要，我重新适应了@Gillespie的函数，以包括上面讨论的修改并可以使用C编程语言进行工作：

FILE * custom_popen(char* command, char type, pid_t* pid)
{
    pid_t child_pid;
    int fd[2];
    pipe(fd);

    if((child_pid = fork()) == -1)
    {
        perror("fork");
        exit(1);
    }

    /* child process */
    if (child_pid == 0)
    {
        if (type == 'r')
        {
            close(fd[0]);    //Close the READ end of the pipe since the child's fd is write-only
            dup2(fd[1], 1); //Redirect stdout to pipe
        }
        else
        {
            close(fd[1]);    //Close the WRITE end of the pipe since the child's fd is read-only
            dup2(fd[0], 0);   //Redirect stdin to pipe
        }

        setpgid(child_pid, child_pid); //Needed so negative PIDs can kill children of /bin/sh
        execl(command, command, (char*)NULL);
        exit(0);
    }
    else
    {
        printf("child pid %d\n", child_pid);
        if (type == 'r')
        {
            close(fd[1]); //Close the WRITE end of the pipe since parent's fd is read-only
        }
        else
        {
            close(fd[0]); //Close the READ end of the pipe since parent's fd is write-only
        }
    }

    *pid = child_pid;

    if (type == 'r')
    {
        return fdopen(fd[0], "r");
    }

    return fdopen(fd[1], "w");
}

int custom_pclose(FILE * fp, pid_t pid)
{
    int stat;

    fclose(fp);
    while (waitpid(pid, &stat, 0) == -1)
    {
        if (errno != EINTR)
        {
            stat = -1;
            break;
        }
    }

    return stat;
}

从popen获得PID

2 个答案: