in reply to Re: Re: Detect Stop Button
in thread Detect Stop Button

hakkr, sevensven's code is just a test that illustrates how to use those signal handlers, and it will let you verify that your server passes the signals to your script appropriately. You don't need to constantly print anything -- that was just part of the test. So, don't slow yourself down needlessly, okay?

On the other hand, if your script will run for quite a while -- 2+ minutes -- then you really should be printing some invisible characters to keep the browser from timing out. Just another CGI trick...

Check out sigtrap. After checking out this doc, I'm about to replace all my signal handler code with one sigtrap line!

Also, check out the great info in the Camel 3 book pp. 412-417 about handling signals and some more specific info on zombie processes.

One last thing: SIG{PIPE} is the signal which should get sent when a user hits the STOP button on their browser. You really should handle those other important signals too, but SIG{PIPE} is the enemy you're dealing with specifically.

Update: Here's my new and improved signal handler.
use Carp;
use sigtrap qw(handler croak normal-signals error-signals);

[download]
Also, the signal I get when I hit the STOP button is actually $SIG{TERM}, not $SIG{PIPE}. So, I lied earlier. :)

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(tye)Re: Just making sure...
by tye (Sage) on Nov 26, 2001 at 23:24 UTC

    Actually, you do have to keep printing as that is the only way you are likely to get SIGPIPE, which is likely the only hope you have if you are already getting defunct CGI processes hanging around.

            - tye (but my friends call me "Tye")
[reply]
      Yup. tye is right. I am wrong. S'ok. I've been wrong before. hehehe.

      use CGI qw(:standard);
use CGI::Carp qw(fatalsToBrowser);
use sigtrap qw(handler croak normal-signals error-signals);

$|=1;
print &header;

for (1..60) {
    # Comment the next line, and see the difference!
    print "$_<BR>\n";
    sleep(1);
}

      [download]
      Run this code and hit the STOP button while it's looping. You'll get $SIG{PIPE} and possibly $SIG{TERM} as well. Comment out the print line, and the script will run to completion -- because, although STDOUT is closed, the script isn't printing. So, it never fails on a write to STDOUT to cause the $SIG{PIPE}.

      Thanks for setting me straight, tye.
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Re: (joealba) Just making sure...
by hakkr (Chaplain) on Nov 27, 2001 at 14:26 UTC
    My script runs for about 1 hr so I had set my Apache TimeOut variable to a huge value (3600). This seems to work for most browsers. I think I'll try your idea of printing blank chars to STDOUT instead. The TimeOut variable effects all requests and probably leaves me with lots of Apache children hanging around.
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