invoking a subprocess using fork&exec in a temporal working directory with redirected stdout and stderr and timeout

system_with_timeout_redirect_tempdir.cpp

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <signal.h>
#include <vector>
#include <string>

int system_with_timeout(std::vector<std::string> args, int timeout, std::string dirname) {
  pid_t pid;

  if ((pid = fork()) == 0) {
    char abspath[PATH_MAX];
    realpath( args[0].c_str(), abspath );

    char** arg = NULL;
    arg = new char*[args.size() + 1 ];
    for( size_t i=0; i<args.size(); i++ ) {
      if( i == 0 ) {
        arg[i] = abspath;
      }
      else {
        arg[i] = (char*) args[i].c_str();
      }
    }
    arg[ args.size() ] = NULL;

    int ret = mkdir( dirname.c_str(), 0700 );
    if( ret != 0 ) {
      std::cerr << "failed to create directory : " << dirname << std::endl;
      exit(1);
    }
    ret = chdir( dirname.c_str() );
    if( ret != 0 ) {
      std::cerr << "failed to change directory : " << dirname << std::endl;
      exit(1);
    }

    int fd_out = open("_stdout", O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
    int fd_err = open("_stderr", O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
    // read only, create a file if not exist, read permission, write permission
    dup2( fd_out, 1 );
    dup2( fd_err, 2 );
    close( fd_out );
    close( fd_err );

    int rc = execvp( arg[0], (char*const*) arg );
    std::cerr << "failed to execute the command. rc : " << rc << std::endl;
    exit(1);
  }
  else if (pid > 0) {
    int status = 0;
    time_t begin = std::time(NULL);
    while( true ) {
      sleep(1);
      int ret = waitpid(pid, &status, WNOHANG);
      if( ret != 0 ) {
        break;
      }

      double diff = std::difftime( std::time(NULL), begin );
      if( diff >= timeout ) {
        std::cerr << "  sending sigint" << std::endl;
        kill( pid, 2 );
      }
    }

    if( WIFEXITED(status) ) {
      return WEXITSTATUS(status);
    }
    else if( WIFSIGNALED(status) ) {
      std::cerr << "signaled by signal" << WTERMSIG(status) << std::endl;
      return -1;
    }
    else {
      std::cerr << "other" << std::endl;
      return -1;
    }
  }

  std::cerr << "failed to fork" << std::endl;
  return -1;
}

int main(int argc, char *argv[])
{
  std::vector<std::string> args;
  args.push_back("/usr/bin/ruby");
  args.push_back("-e");
  args.push_back("puts 'hello'; $stderr.puts 'world'; sleep 3");

  int rc = system_with_timeout( args, 1 , "temp");

  return 0;
}