【发布时间】：2014-09-13 03:18:41
【问题描述】：
首先让我说这里有很多问题。
我的论文的其中一项任务要求我编写一个程序来执行一个子程序，如果它的运行时间（不是 wall-time 而是 user+sys ）超过一个特定值或者它的 RAM 消耗量是大于另一个指定值。
虽然我还没有弄清楚 RAM 部分。我用 setitmer 和 ITIMER_PROF 信号来消磨时间。 （因为 ITIMER_PROF 收集实际的 CPU 使用情况，而不是设置一个时间起点，然后计算 x 时间）
我使用 setitimer 的原因是因为我需要的精度低于秒精度。 （例如，在 1.75 秒（1750000 微秒）后终止进程。setrlimit 方法只有一秒。
问题1为什么不带有ITIME_PROF的setitimer在父进程中设置时不起作用？孩子的 CPU / 系统调用不被它收集？
childPID = fork();
if (childPID == -1){
printf( "Puff paff ... fork() did not work !\n" );
exit(1);
}
// Child
if(childPID == 0) {
execvp(args[0], args);
exit(1);
}
// Parent
else{
// Using a ITIMER_PROF inside the parent program will not work!
// The child may take 1 hour to execute and the parent will wait it out!
// To fix this we need to use a ITIMER_REAL ( wall-time ) but that's not an accurate measurement
struct itimerval timer;
timer.it_value.tv_sec = 0;
timer.it_value.tv_usec = 500000;
timer.it_interval.tv_sec = 0;
timer.it_interval.tv_usec = 500000;
setitimer ( ITIMER_PROF, &timer, NULL);
int status;
waitpid(childPID,&status,0);
if (WIFEXITED(status)) {
fprintf(stderr, "Nice nice, the child exited ... with cPID = %d with status = %d \n", cPID, WEXITSTATUS(status) );
}
}
问题 2 为什么会这样！？ execvp 不会覆盖所有函数（timeout_sigprof、main 和任何其他函数）吗？难道就不能有人在子程序中捕捉到信号并取代原来的函数吗？
void timeout_sigprof( int signum ){
fprintf(stderr, "The alarm SIGPROF is here !\nThe actual pid: %d\n", getpid());
//TODO: Write output and say the child terminated with
// ram or time limit exceeded
exit(105); // Note the 105 !
}
childPID = fork();
if (childPID == -1){
printf( "Puff paff ... fork() did not work !\n" );
exit(1);
}
// Child
if(childPID == 0) {
//
struct sigaction sa;
memset (&sa, 0, sizeof (sa));
sa.sa_handler = &timeout_sigprof;
sigaction (SIGPROF, &sa, NULL);
struct itimerval timer;
timer.it_value.tv_sec = 0;
timer.it_value.tv_usec = 250000;
timer.it_interval.tv_sec = 0;
timer.it_interval.tv_usec = 250000;
setitimer ( ITIMER_PROF, &timer, NULL);
execvp(args[0], args);
exit(1);
}
// Parent process
else {
// Waiting for the child
int status;
waitpid(childPID,&status,0);
if (WIFEXITED(status)) {
fprintf(stderr, "Nice nice, the child exited ... with cPID = %d with status = %d \n", cPID, WEXITSTATUS(status) );
}
exit(0);
}
问题3为什么放在这里的dup2居然会起作用，让我们对孩子的输入/输出进行重定向？
childPID = fork();
if (childPID == -1){
printf( "Puff paff ... fork() did not work !\n" );
exit(1);
}
// Child
if(childPID == 0) {
// Redirect all I/O to/from a file
int outFileId = open("output", O_WRONLY | O_TRUNC | O_CREAT, S_IRUSR | S_IRGRP | S_IWGRP | S_IWUSR);
// Redirect the output for the CHILD program. Still don't know why it works.
dup2(outFileId, 1)
// No idea why these dup2's work ! As i close the file descriptors here ?!
close(outFileId);
execvp(args[0], args);
exit(1);
}
// Parent process
else {
// Waiting for the child
int status;
waitpid(childPID,&status,0);
if (WIFEXITED(status)) {
fprintf(stderr, "Nice nice, the child exited ... with cPID = %d with status = %d \n", cPID, WEXITSTATUS(status) );
}
exit(0);
}
这是我编写的代码，它仅在程序运行 X 时间 (x = 500ms) 后才会终止程序。
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <sys/time.h>
volatile pid_t childPID;
// This function should exist only in the parent! The child show not have it after a exec* acording to :
// The exec() family of functions replaces the current process image with a new process image.
void timeout_sigprof( int signum ){
fprintf(stderr, "The alarm SIGPROF is here !\nThe actual pid: %d\n", getpid());
//TODO: Write output and say the child terminated with a ram or time limit exceeded
exit(105); // Note the 105 !
}
int main(int argc, char *argv[]) {
int cstatus;
pid_t cPID;
char *args[2];
args[0] = "/home/ddanailov/Projects/thesis/programs/prime/prime";
args[1] = NULL; // Indicates the end of arguments.
// Handle the SIGPROF signal in the function time_handler in both the child and
struct sigaction sa;
memset (&sa, 0, sizeof (sa));
sa.sa_handler = &timeout_sigprof;
sigaction (SIGPROF, &sa, NULL);
childPID = fork();
if (childPID == -1){
printf( "Puff paff ... fork() did not work !\n" );
exit(1);
}
// Child
if(childPID == 0) {
struct itimerval timer;
timer.it_value.tv_sec = 0;
timer.it_value.tv_usec = 250000;
timer.it_interval.tv_sec = 0;
timer.it_interval.tv_usec = 250000;
setitimer ( ITIMER_PROF, &timer, NULL);
// Redirect all I/O to/from a file
int outFileId = open("output", O_WRONLY | O_TRUNC | O_CREAT, S_IRUSR | S_IRGRP | S_IWGRP | S_IWUSR);
// int inFileId = open("input");
// Redirect the output for the CHILD program. Still don't know why it works.
//dup2(inFileId, 0);
dup2(outFileId, 1);
//dup2(outFileId, 2);
// No idea why these dup2's work ! As i close the file descriptors here ?!
close(outFileId);
close(inFileId);
execvp(args[0], args);
exit(1);
}
// Parent process
else {
// Waiting for the child
int status;
waitpid(childPID,&status,0);
if (WIFEXITED(status)) {
fprintf(stderr, "Nice nice, the child exited ... with cPID = %d with status = %d \n", cPID, WEXITSTATUS(status) );
}
exit(0);
}
return 0;
}
任何帮助/解释将不胜感激！
提前谢谢大家，
前
【问题讨论】：
-
你真的看到“SIGPROF 警报来了”吗？还是孩子默默退出？
-
嘿@harmic，是的，我确实看到 SIGPROF 在这里，pID 等。您可以使用我粘贴的最后一个完整程序（在孩子体内有 setitimers 的那个）进行测试在 execvp 之前处理）而不是“/home/ddanailov/Projects/thesis/programs/prime/prime”，在此处添加一个需要 1 秒以上的程序。感谢您对此进行调查！
-
顺便说一句，您标记此 C++ 的任何特殊原因？我这里只能看到C代码
-
删除了 C++ 标签。谢谢。我不确定它为什么会在那里。我认为 SO 将其作为建议标签。