Author: stas Date: Wed Nov 24 15:02:27 2004 New Revision: 106486 URL: http://svn.apache.org/viewcvs?view=rev&rev=106486 Log: extra notes on Out of memory problem Submitted by: Brian Hirt <[EMAIL PROTECTED]>
Modified: perl/modperl/docs/trunk/src/docs/1.0/guide/troubleshooting.pod Modified: perl/modperl/docs/trunk/src/docs/1.0/guide/troubleshooting.pod Url: http://svn.apache.org/viewcvs/perl/modperl/docs/trunk/src/docs/1.0/guide/troubleshooting.pod?view=diff&rev=106486&p1=perl/modperl/docs/trunk/src/docs/1.0/guide/troubleshooting.pod&r1=106485&p2=perl/modperl/docs/trunk/src/docs/1.0/guide/troubleshooting.pod&r2=106486 ============================================================================== --- perl/modperl/docs/trunk/src/docs/1.0/guide/troubleshooting.pod (original) +++ perl/modperl/docs/trunk/src/docs/1.0/guide/troubleshooting.pod Wed Nov 24 15:02:27 2004 @@ -667,38 +667,88 @@ See also L<Out of memory|/Out_of_memory_> + + + + =head2 Out of memory! 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: - - =item -DPERL_EMERGENCY_SBRK - - 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 $^M. See perlvar(1) for more details. - -If you compile with that option and add 'C<use Apache::Debug level -=E<gt> 4;>' to your Perl script, it will allocate the C<$^M> emergency -pool and the C<$SIG{__DIE__}> handler will call C<Carp::confess>, -giving you a stack trace which should reveal where the problem is. -See the C<Apache::Resource> module for ways to control httpd -processes. +"Out of memory!" message and/or "Callback called exit". Common causes +of this are never-ending loops, deep recursion, or calling an +undefined subroutine. + +If you are using perl 5.005 or later, and perl is compiled to use it's +own malloc rutines, you can trap out of memory errors by setting aside +an extra memory pool in the special variable C<$^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 +C<$^M>. Run: + + % perl -V:usemymalloc + +if your mod_perl was compiled against perl which uses internal +C<malloc()> the answer will be 'y'. + +Here is an explanation of C<$^M> from the C<perlvar> manpage: + + 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 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<$SIG{__DIE__}> handler will call +C<Carp::confess>, giving you a stack trace which should reveal where +the problem is. See the C<Apache::Resource> module for ways to +control httpd processes. Note that Perl 5.005 and later have C<PERL_EMERGENCY_SBRK> turned on by default. -The other trick is to have a startup script initialize -C<Carp::confess>, like so: +Another trick is to have a startup script initialize C<Carp::confess>, +like so: use Carp (); eval { Carp::confess("init") }; this way, when the real problem happens, C<Carp::confess> doesn't eat memory in the emergency pool (C<$^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 + $main::SIG{__DIE__} = \&CGI::Carp::confess; + +Discussion of C<$^M> has come up on PerlMonks, and there is +speculation that C<$^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 --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
