使用SIGINT默认处理程序时，从system()返回值 [英] Return value from system() when using SIGINT default handler
问题描述
当子进程从终端接收到SIGINT时，我正在经历 system()的一些奇怪的返回值.为了说明，从Perl脚本 parent.pl 中，我使用 system()来运行另一个Perl脚本作为子进程，但是我还需要通过外壳来运行该子进程.，所以我使用了 system'sh'，'-c'，... 形式.因此，子代的父代成为了 sh 进程，而子代的父代成为了 sh 进程. sh 进程变为 parent.pl .另外，为了避免 sh 进程接收到 SIGINT 信号，我将其捕获.
I am experiencing some strange return values from system() when a child process receives a SIGINT from the terminal. To explain, from a Perl script parent.pl I used system() to run another Perl script as a child process, but I also needed to run the child through the shell, so I used the system 'sh', '-c', ... form.. So the parent of the child became the sh process and the parent of the sh process became parent.pl. Also, to avoid having the sh process receiving the SIGINT signal, I trapped it.
例如， parent.pl :
use feature qw(say);
use strict;
use warnings;
for (1..3) {
my $res = system 'sh', '-c', "trap '' INT; child$_.pl";
say "Parent received return value: " . ($res >> 8);
}
其中 child1.pl :
local $SIG{INT} = "DEFAULT";
sleep 10;
say "Child timed out..";
exit 1;
child2.pl :
local $SIG{INT} = sub { die };
sleep 10;
say "Child timed out..";
exit 1;
和 child3.pl 是:
eval {
local $SIG{INT} = sub { die };
sleep 10;
};
if ( $@ ) {
print $@;
exit 2;
}
say "Child timed out..";
exit 0;
如果我从命令行运行 parent.pl 并按CTRL-C中止每个子进程，则输出为:
If I run parent.pl (from the command line) and press CTRL-C to abort each child process, the output is:
^CParent received return value: 130
^CDied at ./child2.pl line 7.
Parent received return value: 4
^CDied at ./child3.pl line 8.
Parent received return value: 2
现在，我想知道为什么案例1的返回值为130，案例2的返回值为4.
Now, I would like to know why I get a return value of 130 for case 1, and a return value of 4 for case 2.
此外，很高兴知道在这种情况下"DEFAULT" 信号处理程序的作用.
Also, it would be nice to know exactly what the "DEFAULT" signal handler does in this case.
注意:如果我将 sh 替换为 bash (并捕获 SIGINT 而不是 INT ，则会返回相同的值>在 bash 中).
Note: the same values are returned if I replace sh with bash ( and trap SIGINT instead of INT in bash ).
另请参阅:
推荐答案
此问题与在使用时向父级传播信号非常相似系统，您之前曾问过.
This question is very similar to Propagation of signal to parent when using system that you asked earlier.
来自我的bash文档:
From my bash docs:
当命令在致命信号N上终止时，bash将使用128 + N的值作为退出状态.
When a command terminates on a fatal signal N, bash uses the value of 128+N as the exit status.
SIGINT通常为2，因此128 + 2等于130.
SIGINT is typically 2, so 128 + 2 give you 130.
Perl的 die 通过检查 $！找出其退出代码！/code>或 $?来捕获未捕获的异常(因此，使用 eval 的情况并非如此):
Perl's die figures out its exit code by inspecting $! or $? for an uncaught exception (so, not the case where you use eval):
exit $! if $!; # errno
exit $? >> 8 if $? >> 8; # child exit status
exit 255; # last resort
请注意，在这种情况下，Perl会以原样的值退出，而不会上移8位.
Notice that in this case, Perl exits with the value as is, not shifted up 8 bits.
errno值恰好为4(请参见 errno.h ). $！变量是具有不同字符串和数字值的对偶变量.以数字方式使用它(如加零)以获取数字面:
The errno value happens to be 4 (see errno.h). The $! variable is a dualvar with different string and numeric values. Use it numerically (like adding zero) to get the number side:
use v5.10;
local $SIG{INT}=sub{
say "numeric errno is ", $!+0;
die
};
sleep 10;
print q(timed out);
exit 1;
此打印:
$ bash -c "perl errno.pl"
^Cnumeric errno is 4
Died at errno.pl line 6.
$ echo $?
4
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