Brian Hirt wrote:
I've typed up my suggestions to the troubleshooting doc, and
incorporated glen's suggestions too. Stas wants me to post to the list
to see if there are any comments / corrections.
I wasn't sure if I should put a comment in about __DIE__ handlers and
their use with evals, it seemed like that might be too general perl.
Thanks Brian, very late but now committed.
Index: src/docs/1.0/guide/troubleshooting.pod
===================================================================
RCS file:
/home/cvspublic/modperl-docs/src/docs/1.0/guide/troubleshooting.pod,v
retrieving revision 1.28
diff -u -r1.28 troubleshooting.pod
--- src/docs/1.0/guide/troubleshooting.pod 5 May 2004 03:29:38
-0000 1.28
+++ src/docs/1.0/guide/troubleshooting.pod 6 May 2004 22:40:07 -0000
@@ -589,27 +589,45 @@
If something goes really wrong with your code, Perl may die with an
"Out of memory!" message and/or "Callback called exit". Common causes
of this
-are never-ending loops, deep recursion, or calling an
-undefined subroutine. Here's one way to catch the problem: See Perl's
-INSTALL document for this item:
+are never-ending loops, deep recursion, or calling an undefined
subroutine.
- =item -DPERL_EMERGENCY_SBRK
+If you are using perl 5.005 or later, and perl is compiled to use it's
own
+malloc rutines, you can trap out of memory errors by setting aside an
extra
+memory pool in the special variable $^M. By default perl uses the
operating
+system malloc for many popular systems, so unless you build perl with
+'usemymalloc=y' you probably wont be able to use $^M. To check if your
mod_perl
+was compiled to use perl's internal malloc(), stick the following code
in a
+handler and see if usemymalloc is set to 'y'
+
+ use Config;
+
+ print Config::myconfig();
+
+Here is an explanation of $^M from perlvar(i):
+
+ $^M By default, running out of memory is an untrap-
+ pable, fatal error. However, if suitably built,
+ Perl can use the contents of $^M as an emergency
+ memory pool after die()ing. Suppose that your
+ Perl were compiled with -DPERL_EMERGENCY_SBRK and
+ used Perl's malloc. Then
+
+ $^M = 'a' x (1 << 16);
+
+ would allocate a 64K buffer for use in an emer-
+ gency. See the INSTALL file in the Perl distribu-
+ tion for information on how to enable this option.
+ To discourage casual use of this advanced feature,
+ there is no English long name for this variable.
- If PERL_EMERGENCY_SBRK is defined, running out of memory need not be a
- fatal error: a memory pool can allocated by assigning to the special
- variable $^M. See perlvar(1) for more details.
-
-If you compile with that option and add 'C<use Apache::Debug level
+If your perl installation supports $^M and you add 'C<use Apache::Debug
level
=E<gt> 4;>' to your Perl script, it will allocate the C<$^M> emergency
pool and the C<$SIG{__DIE__}> handler will call C<Carp::confess>,
giving you a stack trace which should reveal where the problem is.
See the C<Apache::Resource> module for ways to control httpd
processes.
-Note that Perl 5.005 and later have C<PERL_EMERGENCY_SBRK> turned on
-by default.
-
-The other trick is to have a startup script initialize
+Another trick is to have a startup script initialize
C<Carp::confess>, like so:
use Carp ();
@@ -617,6 +635,24 @@
this way, when the real problem happens, C<Carp::confess> doesn't eat
memory in the emergency pool (C<$^M>).
+
+Some other mod_perl users have reported that this works well for them:
+
+ ## Allocate 64K as an emergency memory pool for use in out of
memory situation
+ $^M = 0x00 x 65536;
+
+ ## Little trick to initialize this routine here so that in the case
of OOM,
+ ## compiling this routine doesn't eat memory from the emergency
memory pool $^M
+ use CGI::Carp ();
+ eval { CGI::Carp::confess('init') };
+
+ ## Importing CGI::Carp sets $main::SIG{__DIE__} = \&CGI::Carp::die;
+ ## Override that to additionally give a stack backtrace
+ $main::SIG{__DIE__} = \&CGI::Carp::confess;
+
+Discussion of $^M has come up on PerlMonks, and there is speculation
that $^M is a
+forgotten feature that's not well supported. See
+http://perlmonks.org/index.pl?node_id=287850 for more information.
=head2 server reached MaxClients setting, consider raising the
MaxClients setting
--
__________________________________________________________________
Stas Bekman JAm_pH ------> Just Another mod_perl Hacker
http://stason.org/ mod_perl Guide ---> http://perl.apache.org
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