标准输出影响SIGKILL? [英] standard output impact SIGKILL?
问题描述
我有一个脚本来限制命令的执行时间.
I have a script to limit the execution time length of commands.
limit.php
<?php
declare(ticks = 1);
if ($argc<2) die("Wrong parameter\n");
$cmd = $argv[1];
$tl = isset($argv[2]) ? intval($argv[2]) : 3;
$pid = pcntl_fork();
if (-1 == $pid) {
die('FORK_FAILED');
} elseif ($pid == 0) {
exec($cmd);
posix_kill(posix_getppid(), SIGALRM);
} else {
pcntl_signal(SIGALRM, create_function('$signo',"die('EXECUTE_ENDED');"));
sleep($tl);
posix_kill($pid, SIGKILL);
die("TIMEOUT_KILLED : $pid");
}
然后我用一些命令测试此脚本.
Then I test this script with some commands.
测试A
php limit.php "php -r 'while(1){sleep(1);echo PHP_OS;}'" 3
3秒后，我们可以发现进程已按预期终止.
After 3s, we can find the processes were killed as we expected.
测试B
删除输出代码，然后再次运行.
Remove the output code and run again.
php limit.php "php -r 'while(1){sleep(1);}'" 3
结果看起来不太好，由函数"exec"创建的进程没有像测试A那样被杀死.
Result looks not good, the process created by function "exec" was not killed like TEST A.
[alix@s4 tmp]$ ps aux | grep whil[e]
alix 4433 0.0 0.1 139644 6860 pts/0 S 10:32 0:00 php -r while(1){sleep(1);}
系统信息
[alix@s4 tmp]$ uname -a
Linux s4 2.6.18-308.1.1.el5 #1 SMP Wed Mar 7 04:16:51 EST 2012 x86_64 x86_64 x86_64 GNU/Linux
[alix@s4 tmp]$ php -v
PHP 5.3.9 (cli) (built: Feb 15 2012 11:54:46)
Copyright (c) 1997-2012 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2012 Zend Technologies
为什么进程在TEST A中被杀死，而在TEST B中没有?输出是否会影响SIGKILL?
Why the processes killed in TEST A but not in TEST B? Does the output impact the SIGKILL?
有什么建议吗?
推荐答案
在php -r 'while(1){sleep(1);echo PHP_OS;}(process C)和它的父级(process B)之间有一个PIPE，posix_kill($pid, SIGKILL)发送KILL信号到process B，然后process B被终止，但是process C对信号一无所知，并继续运行，并在process C接收到SIGPIPE信号但不知道时将某些内容输出到broken pipe如何处理它以便退出.
There is a PIPE between php -r 'while(1){sleep(1);echo PHP_OS;} (process C) and it's parent (process B), posix_kill($pid, SIGKILL) sends KILL signal to process B, then process B is terminated, but process C doesn't know anything about the signal and continues to run and outputs something to the broken pipe, when process C receives the SIGPIPE signal but has no idea how to handle it so it exits.
您可以使用strace验证它(运行php limit.php "strace php -r 'while(1){sleep(1); echo PHP_OS;};'" 1)，您将看到类似以下内容:
You can verify it with strace (run php limit.php "strace php -r 'while(1){sleep(1); echo PHP_OS;};'" 1), and you will see something like this:
14:43:49.254809 write(1, "Linux", 5) = -1 EPIPE (Broken pipe)
14:43:49.254952 --- SIGPIPE (Broken pipe) @ 0 (0) ---
14:43:49.255110 close(2) = 0
14:43:49.255212 close(1) = 0
14:43:49.255307 close(0) = 0
14:43:49.255402 munmap(0x7fb0762f2000, 4096) = 0
14:43:49.257781 munmap(0x7fb076342000, 1052672) = 0
14:43:49.258100 munmap(0x7fb076443000, 266240) = 0
14:43:49.258268 munmap(0x7fb0762f3000, 323584) = 0
14:43:49.258555 exit_group(0) = ?
关于php -r 'while(1){sleep(1);}，因为broken pipe的父项去世后没有发生，所以它继续按预期运行.
As to php -r 'while(1){sleep(1);}, because there is no broken pipe occurs after it's parent dies, so it continues to run as expected.
通常来说，您应该杀死整个进程组，但如果要杀死它的子进程，则不仅要杀死进程本身，还可以使用PHP杀死process B到其自己的进程组中，然后杀死整个进程组，这是您代码的差异:
Generally speaking, you should kill the whole process group but not only the process itself if you want to kill it's children too, with PHP you can add process B to its own process group, and kill the whole group then, here is the diff with your code:
--- limit.php 2012-08-11 20:50:22.000000000 +0800
+++ limit-new.php 2012-08-11 20:50:39.000000000 +0800
@@ -9,11 +9,13 @@
if (-1 == $pid) {
die('FORK_FAILED');
} elseif ($pid == 0) {
+ $_pid = posix_getpid();
+ posix_setpgid($_pid, $_pid);
exec($cmd);
posix_kill(posix_getppid(), SIGALRM);
} else {
pcntl_signal(SIGALRM, create_function('$signo',"die('EXECUTE_ENDED');"));
sleep($tl);
- posix_kill($pid, SIGKILL);
+ posix_kill(-$pid, SIGKILL);
die("TIMEOUT_KILLED : $pid");
}
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