Kill a hanging child process

Question

My Perl script launches an external program (which takes one command line parameter) and processes its output. I originally did this:

my @result = `prog arg`;

However, it turns out that the program does not work correctly and hangs unpredictably in rare cases. How can I kill a program if it did not exit after a certain time? The script should work on both Windows and Linux, and I understand that alarms and plugs do not work (or at all) on Windows.

I found a module called IPC :: Run , but I cannot figure out how to use it correctly from its documentation. :-( I tried this:

use strict;
use warnings;
use IPC::Run qw(run timeout);
my $in;
my $out;
my $err;
my @result;
my @cmd = qw(prog arg);
run \@cmd, \$in, \$out, \$err, timeout (10) or die "@cmd: $?";
push @result, $_ while (<$out>);
close $out;
print @result;

, 60 , stdout . , 60 ( 10 , -) :

IPC::Run: timeout on timer #1 at C:/Bin/Unix/Perl/site/lib/IPC/Run.pm line 2956

, Proc:: Reliable. , , . , ! :

use strict;
use warnings;
use Proc::Reliable;

my $proc = Proc::Reliable->new ();
$proc->maxtime (10);
my $out = $proc->run ("prog arg");
print "$out\n";

10 . . 5 . , 10- -, , stdout $out. ! script .

, ? ( .) .

Answer 1

my $pid;
if ($^O eq 'MSWin32') {
    $pid = system 1, "prog arg";    # Win32 only, run proc in background
} else {
    $pid = fork();
    if (defined($pid) && $pid == 0) {
        exec("proc arg");
    }
}

my $poor_mans_alarm = "sleep 1,kill(0,$pid)||exit for 1..$TIMEOUT;kill -9,$pid";
system($^X, "-e", $poor_mans_alarm);

. , $pid. , . $ , ( 9, , -9 , . kill 9,... ).

:. ? backticks - , , .

1) , ,

$pid = system 1, "proc arg > some_file";
... start poor man alarm, wait for program to finish ...
open my $fh, '<', 'some_file';
my @process_output = <$fh>;
...

2) Perl open,

$pid = open my $proc, '-|', 'proc arg';
if (fork() == 0) {
    # run poor man alarm in a background process
    exec($^X, '-e', "sleep 1,kill 0,$pid||exit ...");
}
my @process_output = ();
while (<$proc>) {
   push @process_output, $_;
}

while , , .

Answer 2

, . , Windows, .

#!/usr/bin/perl

use strict;
use warnings;
use File::Temp;
use Win32::Process qw(STILL_ACTIVE NORMAL_PRIORITY_CLASS);

my $pid;
my $timeout = 10;
my $prog = "prog arg";
my @output;

if ($^O eq "MSWin32")
{
    my $exitcode;
    my $fh = File::Temp->new ();
    my $output_file = $fh->filename;
    close ($fh);
    open (OLDOUT, ">&STDOUT");
    open (STDOUT, ">$output_file" ) || die ("Unable to redirect STDOUT to $output_file.\n");
    Win32::Process::Create ($pid, $^X, $prog, 1, NORMAL_PRIORITY_CLASS, '.') or die Win32::FormatMessage (Win32::GetLastError ());
    for (1 .. $timeout)
    {
        $pid->GetExitCode ($exitcode);
        last if ($exitcode != STILL_ACTIVE);
        sleep 1;
    }
    $pid->GetExitCode ($exitcode);
    $pid->Kill (0) or die "Cannot kill '$pid'" if ($exitcode == STILL_ACTIVE);
    close (STDOUT);
    open (STDOUT, ">&OLDOUT");
    close (OLDOUT);
    open (FILE, "<$output_file");
    push @output, $_ while (<FILE>);
    close (FILE);
}
else
{
    $pid = open my $proc, "-|", $prog;
    exec ($^X, "-e", "sleep 1, kill (0, $pid) || exit for 1..$timeout; kill -9, $pid") unless (fork ());
    push @output, $_ while (<$proc>);
    close ($proc);
}
print "Output:\n";
print @output;

Answer 3

You might want to use a system call, as in the perldoc -f signal.