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Date: Wed, 15 Aug 2007 18:22:18 +0100
From: George <george AT alink DOT co DOT za>
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To: cygwin AT cygwin DOT com
Subject: Re: Trouble with perl fork() and exec()
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I've just found something in an strace:

**********************************************^M
Program name: C:\cygwin\bin\perl.exe (windows pid 5936)^M
App version:  1005.24, api: 0.156^M
DLL version:  1005.24, api: 0.156^M
DLL build:    2007-01-31 10:57^M
OS version:   Windows NT-5.2^M
Date/Time:    2007-08-15 18:04:46^M
**********************************************^M
   114     376 [main] perl (5936) child_copy: cygheap - hp 0x67C low 
0x611668E0, high 0x6116BBF8, res 1^M
    47     423 [main] perl (5936) child_copy: done^M
    70     493 [main] perl (5936) open_shared: name (null), n 4, shared 
0x60000000 (wanted 0x60000000), h 0xEC^M
    99     592 [main] perl (5936) heap_init: heap base 0x10410000, heap 
top 0x10760000^M
    62     654 [main] perl (5936) open_shared: name (null), n 1, shared 
0x60010000 (wanted 0x60010000), h 0xF0^M
    43     697 [main] perl (5936) user_shared_initialize: opening user 
shared for '' at 0x60010000^M
    44     741 [main] perl (5936) user_shared_initialize: user shared 
version B1D50001^M
    58     799 [main] perl (5936) open_shared: name (null), n 2, shared 
0x60040000 (wanted 0x60040000), h 0xF4^M
   186     985 [main] perl (5936) open_shared: name 
Global\cygwin1S4.cygpid.5936, n 5936, shared 0x60030000 (wanted 
0x60030000), h 0x768^M
    54    1039 [main] perl 5936 set_myself: myself->dwProcessId 5936^M
    84    1123 [main] perl 5936 child_copy: dll data - hp 0x67C low 
0x61100000, high 0x61104BA0, res 1^M
12277544 12278667 [main] perl 5936 child_copy: dll bss - hp 0x67C low 
0x6113F000, high 0x611483D0, res 1^M
  6188 12284855 [main] perl 5936 child_copy: user heap - hp 0x67C low 
0x10410000, high 0x10760000, res 1^M
    92 12284947 [main] perl 5936 child_copy: done^M
   108 12285055 [main] perl 5936 child_copy: data - hp 0x67C low 
0x408000, high 0x408010, res 1^M
    98 12285153 [main] perl 5936 child_copy: bss - hp 0x67C low 
0x40A000, high 0x40A0F0, res 1^M
    56 12285209 [main] perl 5936 child_copy: done^M

It would seem the dll bss copy is taking 12 seconds.

The machine running this is a quad xeon with 16Gb ram so it shouldn't 
have any issue with power (cpu is very low).  Can I give any data to 
help debug this?

George wrote:
> Hello,
> 
> I have a cygwin installation under which I'm running the 
> Net::Server::Fork daemon "munin-node".  For those not aware, munin is a 
> monitoring system which is really easy to use and configure 
> (http://munin.projects.linpro.no).
> 
> That said, it's not working properly.
> 
> Here's the trouble I'm having - maybe somebody has seen it before and 
> can push me in the right direction?
> 
> The basic flow of the daemon is:
> 
> <start munin-node which attaches to a port and runs fine>
> <connect from other machine1>
> <machine1 request plugin>
> <server forks() and then exec() the 'plugin' to gather data>
> <plugin returns data to parent via STDIN>
> <plugin exits>
> <parent returns data to machine1>
> <sing songs, drink beer>
> 
> Now, this is breaking unfortunately, so I never get to sing songs and 
> drink beer.
> 
> What seems to happen is the child gets fork()ed and then the plugin code 
> exec()'d.  The data then comes back up the line via the STDIN to the 
> parent, however, despite the child finishing execution (I've made sure 
> all sockets are closed and even tried a die()) it never exits.
> 
> I've made the sure the data is actually coming back by putting a print 
> in the while loop and that shows that it's coming back from the child. 
> All the data makes it back, but the while loop doesn't finish and the 
> timeout alarm hits, so the child gets reaped.  When it's reaped it 
> returns "Interrupted system call".
> 
> Ive tried replacing the exec() with a dirty hack of system();exit(); but 
> exactly the same thing happens.
> 
> The relevant code which does the running of the plugin is below:
> 
> (Full code: 
> http://munin.projects.linpro.no/browser/branches/1.2-stable/node/munin-node.in) 
> 
> 
> 
> ..
>     print "# Forking .. \n" if $DEBUG;
>     if ($child = open (CHILD, "-|")) {
>       eval {
>           local $SIG{ALRM} = sub { $timed_out=1; die "$!\n"};
>           alarm($timeout);
>           while(<CHILD>) {
>             #last if $_ eq "# DONE";
>             if ($_ eq "# DONE") { close(CHILD); }
>             push @lines,$_;
>             print "#DEBUG CHILD: $_" if $DEBUG;
>           }
>           print "# Finished gathering data from Child\n" if $DEBUG;
>       };
>       if( $timed_out ) {
>           print "# Child timed out - calling reap_children $@ \n" if 
> $DEBUG;
>           reap_children($child, "$service $command: $@");
>           close (CHILD);
>           return ();
>       }
>       unless (close CHILD)
>       {
>           if ($!)
>           {
>               # If Net::Server::Fork is currently taking care of reaping,
>               # we get false errors. Filter them out.
>               unless (defined $autoreap and $autoreap)
>               {
>                   logger ("Error while executing plugin \"$service\": $!");
>               }
>           }
>           else
>           {
>               logger ("Plugin \"$service\" exited with status $?. 
> --@lines--");
>           }
>       }
>     else {
>       if ($child == 0) {
>         my $timenow = localtime();
>         print "# Child forked as $$ - $timenow\n" if $DEBUG;
>         # New process group...
>         POSIX::setsid();
> 
>         ..
>         <child stuff here>
>         ..
> 
>             print "# Execing $servicedir/$service $command\n" if $DEBUG;
>             exec ("$servicedir/$service", $command);
> 
>     ..
> 
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