Perl subroutine timeout

Question

I have a subroutine that normally takes 1 second to run. Sometimes, it can run infinitely. I want to move on in the code if the subroutine is taking too long (> 10 seconds) and ignore that run of that subroutine. Here is what I have so far using alarm.

use Win32::OLE;

eval { 
    local $SIG{ALRM} = sub { die "alarm\n" };
    alarm 10;                   # schedule alarm in 10 seconds 
    &do_the_subroutine;
    alarm 0;                    # cancel the alarm
};

if ($@) {
    $error_string .= $script;
    #Do something else if the subroutine took too long.
}

do_the_subroutine{
# use existing instance if Excel is already running
    eval {$ex = Win32::OLE->GetActiveObject('Excel.Application')};
    die "Excel not installed" if $@;
    unless (defined $ex) {
        $ex = Win32::OLE->new('Excel.Application', sub {$_[0]->Quit;})
                or die "Oops, cannot start Excel";
    }

    # get a new workbook
    $book = $ex->Workbooks->Add;

    # write to a particular cell
    $sheet = $book->Worksheets(1);
    $sheet->Cells(1,1)->{Value} = "foo";

    # write a 2 rows by 3 columns range
    $sheet->Range("A8:C9")->{Value} = [[ undef, 'Xyzzy', 'Plugh' ],
                                       [ 42,    'Perl',  3.1415  ]];

    # print "XyzzyPerl"
    $array = $sheet->Range("A8:C9")->{Value};
    for (@$array) {
        for (@$_) {
            print defined($_) ? "$_|" : "<undef>|";
        }
        print "\n";
    }

    # save and exit
    $book->SaveAs( 'test.xls' );
    undef $book;
    undef $ex;
}

&do_the_subroutine never returns so I'm not able to move on. I'm also not able to put this block of code inside that subroutine. Any thoughts?

Merriment

Could you share the subroutine's code? It works fine for me, see this demo: ideone.com/KycD4S – Indent

I can't seem to recreate this behavior, using the same code I see the alarm going off. Is there more code that we are not seeing here? Can you show the definition of do_the_subroutine? – Pylorectomy

Hello, I have added the definition. – Merriment

The OLE stuff looks like it could be slow. – Heiser

@Heiser yes.. hence why I am doing this. – Merriment

I wonder if the alarm signal thing is handled differently with Windows signals. – Aqua

What is your question? Would this be a better fit for codereview.stackexchange.com? – Academy

@Academy the question is: How to make it quit the subroutine after 10 seconds. – Merriment

I was thinking along those lines @sobrique. But also maybe that it runs something external and for that the handler isn't invoked. So I tried to use sub do_the_sub { system 'sleep 15' } on my Linux box. Works just the same. No problems visible. We need a Windows box. – Heiser

<sarcasm>Maybe if you change that comment from schedule alarm in 15 seconds to 10 seconds... </sarcam> :) – Heiser

@Academy This question would be off-topic for CR. This is about hunting down a known bug and altering functionality of code. Please read A Guide to Code Review for Stack Overflow users – Brennabrennan

@SimonAndréForsberg, yes, thanks. I'd misunderstood the OP's "&dosub never returns" remark to simply be a restatement of his "sometimes it can run infinitely." – Academy

FWIW perlmonks.org/?node_id=505473 also seems to indicate OLE doesn't play well with alarm. perhaps move the work to a child process or a thread? – Cougar

of course, the other question might be - why does that sub 'stall' - it doesn't look like it should infinite loop or anything. – Aqua

as to why it stalls, on my Windows box I got a pop-up from Microsoft Excel asking "A file named 'test.xls' already exists in this location. Do you want to replace it?". I assume the hang is based on that. – Greatly

Answer 1

I suspect that what you want to do is simply not natively possible with alarm on Windows.

From perldoc perlport:

alarm Emulated using timers that must be explicitly polled whenever Perl wants to dispatch "safe signals" and therefore cannot interrupt blocking system calls. (Win32)

Greatly

Thought it might be something like that. Well done for doing the digging :) – Aqua