[编辑：在文中添加MCVE，澄清]
我有以下程序使用RLIMIT_CPU将setrlimit()设置为2秒并捕获信号。 RLIMIT_CPU限制了CPU时间。 «当进程达到软限制时，会发送SIGXCPU信号。此信号的默认操作是终止该过程。但是，可以捕获信号，处理程序可以将控制权返回给主程序。»（man）
以下程序设置RLIMIT_CPU和SIGXCPU的信号处理程序，然后它会生成随机数，直到SIGXCPU被引发，信号处理程序才会退出程序。
test_signal.cpp
/*
* Test program for signal handling on CMS.
*
* Compile with:
* /usr/bin/g++ [-DDEBUG] -Wall -std=c++11 -O2 -pipe -static -s \
* -o test_signal test_signal.cpp
*
* The option -DDEBUG activates some debug logging in the helpers library.
*/
#include <iostream>
#include <fstream>
#include <random>
#include <chrono>
#include <iostream>
#include <unistd.h>
#include <csignal>
#include <sys/time.h>
#include <sys/resource.h>
using namespace std;
namespace helpers {
long long start_time = -1;
volatile sig_atomic_t timeout_flag = false;
unsigned const timelimit = 2; // soft limit on CPU time (in seconds)
void setup_signal(void);
void setup_time_limit(void);
static void signal_handler(int signum);
long long get_elapsed_time(void);
bool has_reached_timeout(void);
void setup(void);
}
namespace {
unsigned const minrand = 5;
unsigned const maxrand = 20;
int const numcycles = 5000000;
};
/*
* Very simple debugger, enabled at compile time with -DDEBUG.
* If enabled, it prints on stderr, otherwise it does nothing (it does not
* even evaluate the expression on its right-hand side).
*
* Main ideas taken from:
* - C++ enable/disable debug messages of std::couts on the fly
* (https://stackoverflow.com/q/3371540/2377454)
* - Standard no-op output stream
* (https://stackoverflow.com/a/11826787/2377454)
*/
#ifdef DEBUG
#define debug true
#else
#define debug false
#endif
#define debug_logger if (!debug) \
{} \
else \
cerr << "[DEBUG] helpers::"
// conversion factor betwen seconds and nanoseconds
#define NANOS 1000000000
// signal to handle
#define SIGNAL SIGXCPU
#define TIMELIMIT RLIMIT_CPU
/*
* This could be a function factory where and a closure of the signal-handling
* function so that we could explicitly pass the output ofstream and close it.
* C++ support closures only for lambdas, alas, at the moment we also need
* the signal-handling function to be a pointer to a function and lambaa are
* a different object that can not be converted. See:
* - Passing lambda as function pointer
* (https://stackoverflow.com/a/28746827/2377454)
*/
void helpers::signal_handler(int signum) {
helpers::timeout_flag = true;
debug_logger << "signal_handler:\t" << "signal " << signum \
<< " received" << endl;
debug_logger << "signal_handler:\t" << "exiting after " \
<< helpers::get_elapsed_time() << " microseconds" << endl;
exit(0);
}
/*
* Set function signal_handler() as handler for SIGXCPU using sigaction. See
* - https://stackoverflow.com/q/4863420/2377454
* - https://stackoverflow.com/a/17572787/2377454
*/
void helpers::setup_signal() {
debug_logger << "set_signal:\t" << "set_signal() called" << endl;
struct sigaction new_action;
//Set the handler in the new_action struct
new_action.sa_handler = signal_handler;
// Set to empty the sa_mask. It means that no signal is blocked
// while the handler run.
sigemptyset(&new_action.sa_mask);
// Block the SIGXCPU signal, while the handler run, SIGXCPU is ignored.
sigaddset(&new_action.sa_mask, SIGNAL);
// Remove any flag from sa_flag
new_action.sa_flags = 0;
// Set new action
sigaction(SIGNAL,&new_action,NULL);
if(debug) {
struct sigaction tmp;
// read the old signal associated to SIGXCPU
sigaction(SIGNAL, NULL, &tmp);
debug_logger << "set_signal:\t" << "action.sa_handler: " \
<< tmp.sa_handler << endl;
}
return;
}
/*
* Set soft CPU time limit.
* RLIMIT_CPU set teg CPU time limit in seconds..
* See:
* - https://www.go4expert.com/articles/
* getrlimit-setrlimit-control-resources-t27477/
* - https://gist.github.com/Leporacanthicus/11086960
*/
void helpers::setup_time_limit(void) {
debug_logger << "set_limit:\t\t" << "set_limit() called" << endl;
struct rlimit limit;
if(getrlimit(TIMELIMIT, &limit) != 0) {
perror("error calling getrlimit()");
exit(EXIT_FAILURE);
}
limit.rlim_cur = helpers::timelimit;
if(setrlimit(TIMELIMIT, &limit) != 0) {
perror("error calling setrlimit()");
exit(EXIT_FAILURE);
}
if (debug) {
struct rlimit tmp;
getrlimit(TIMELIMIT, &tmp);
debug_logger << "set_limit:\t\t" << "current limit: " << tmp.rlim_cur \
<< " seconds" << endl;
}
return;
}
void helpers::setup(void) {
struct timespec start;
if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start)) {
exit(EXIT_FAILURE);
}
start_time = start.tv_sec*NANOS + start.tv_nsec;
setup_signal();
setup_time_limit();
return;
}
long long helpers::get_elapsed_time(void) {
struct timespec current;
if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, ¤t)) {
exit(EXIT_FAILURE);
}
long long current_time = current.tv_sec*NANOS + current.tv_nsec;
long long elapsed_micro = (current_time - start_time)/1000 + \
((current_time - start_time) % 1000 >= 500);
return elapsed_micro;
}
bool helpers::has_reached_timeout(void) {
return helpers::timeout_flag;
}
int main() {
helpers::setup();
ifstream in("input.txt");
in.close();
ofstream out("output.txt");
random_device rd;
mt19937 eng(rd());
uniform_int_distribution<> distr(minrand, maxrand);
int i = 0;
while(!helpers::has_reached_timeout()) {
int nmsec;
for(int n=0; n<numcycles; n++) {
nmsec = distr(eng);
}
cout << "i: " << i << "\t- nmsec: " << nmsec << "\t- ";
out << "i: " << i << "\t- nmsec: " << nmsec << "\t- ";
cout << "program has been running for " << \
helpers::get_elapsed_time() << " microseconds" << endl;
out << "program has been running for " << \
helpers::get_elapsed_time() << " microseconds" << endl;
i++;
}
return 0;
}
我按如下方式编译：
/usr/bin/g++ -DDEBUG -Wall -std=c++11 -O2 -pipe -static -s -o test_signal test_signal.cpp
在我的笔记本电脑上，它在2秒后正确获得SIGXCPU，请参阅输出：
$ /usr/bin/time -v ./test_signal
[DEBUG] helpers::set_signal: set_signal() called
[DEBUG] helpers::set_signal: action.sa_handler: 1
[DEBUG] helpers::set_limit: set_limit() called
[DEBUG] helpers::set_limit: current limit: 2 seconds
i: 0 - nmsec: 11 - program has been running for 150184 microseconds
i: 1 - nmsec: 18 - program has been running for 294497 microseconds
i: 2 - nmsec: 9 - program has been running for 422220 microseconds
i: 3 - nmsec: 5 - program has been running for 551882 microseconds
i: 4 - nmsec: 20 - program has been running for 685373 microseconds
i: 5 - nmsec: 16 - program has been running for 816642 microseconds
i: 6 - nmsec: 9 - program has been running for 951208 microseconds
i: 7 - nmsec: 20 - program has been running for 1085614 microseconds
i: 8 - nmsec: 20 - program has been running for 1217199 microseconds
i: 9 - nmsec: 12 - program has been running for 1350183 microseconds
i: 10 - nmsec: 17 - program has been running for 1486431 microseconds
i: 11 - nmsec: 13 - program has been running for 1619845 microseconds
i: 12 - nmsec: 20 - program has been running for 1758074 microseconds
i: 13 - nmsec: 11 - program has been running for 1895408 microseconds
[DEBUG] helpers::signal_handler: signal 24 received
[DEBUG] helpers::signal_handler: exiting after 2003326 microseconds
Command being timed: "./test_signal"
User time (seconds): 1.99
System time (seconds): 0.00
Percent of CPU this job got: 99%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:02.01
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 1644
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 59
Voluntary context switches: 1
Involuntary context switches: 109
Swaps: 0
File system inputs: 0
File system outputs: 16
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0
如果我在虚拟机（VirtualBox，运行Ubuntu）中编译并运行，我会得到这个：
$ /usr/bin/time -v ./test_signal
[DEBUG] helpers::set_signal: set_signal() called
[DEBUG] helpers::set_signal: action.sa_handler: 1
[DEBUG] helpers::set_limit: set_limit() called
[DEBUG] helpers::set_limit: current limit: 2 seconds
i: 0 - nmsec: 12 - program has been running for 148651 microseconds
i: 1 - nmsec: 13 - program has been running for 280494 microseconds
i: 2 - nmsec: 7 - program has been running for 428390 microseconds
i: 3 - nmsec: 5 - program has been running for 580805 microseconds
i: 4 - nmsec: 10 - program has been running for 714362 microseconds
i: 5 - nmsec: 19 - program has been running for 846853 microseconds
i: 6 - nmsec: 20 - program has been running for 981253 microseconds
i: 7 - nmsec: 7 - program has been running for 1114686 microseconds
i: 8 - nmsec: 7 - program has been running for 1249530 microseconds
i: 9 - nmsec: 12 - program has been running for 1392096 microseconds
i: 10 - nmsec: 20 - program has been running for 1531859 microseconds
i: 11 - nmsec: 19 - program has been running for 1667021 microseconds
i: 12 - nmsec: 13 - program has been running for 1818431 microseconds
i: 13 - nmsec: 17 - program has been running for 1973182 microseconds
i: 14 - nmsec: 7 - program has been running for 2115423 microseconds
i: 15 - nmsec: 20 - program has been running for 2255140 microseconds
i: 16 - nmsec: 13 - program has been running for 2394162 microseconds
i: 17 - nmsec: 10 - program has been running for 2528274 microseconds
i: 18 - nmsec: 15 - program has been running for 2667978 microseconds
i: 19 - nmsec: 8 - program has been running for 2803725 microseconds
i: 20 - nmsec: 9 - program has been running for 2940610 microseconds
i: 21 - nmsec: 19 - program has been running for 3075349 microseconds
i: 22 - nmsec: 14 - program has been running for 3215255 microseconds
i: 23 - nmsec: 5 - program has been running for 3356515 microseconds
i: 24 - nmsec: 5 - program has been running for 3497369 microseconds
[DEBUG] helpers::signal_handler: signal 24 received
[DEBUG] helpers::signal_handler: exiting after 3503271 microseconds
Command being timed: "./test_signal"
User time (seconds): 3.50
System time (seconds): 0.00
Percent of CPU this job got: 99%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.52
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 1636
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 59
Voluntary context switches: 0
Involuntary context switches: 106
Swaps: 0
File system inputs: 0
File system outputs: 16
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0
即使运行在我的笔记本电脑上编译的二进制文件，该过程也会在用户时间过去约3秒后被杀死。
有什么可能导致这种情况的想法？有关更广泛的上下文，请参阅此主题：https://github.com/cms-dev/cms/issues/851