Apache::Reload
RELOAD(1) User Contributed Perl Documentation RELOAD(1)
NAME
Apache::Reload - Reload Perl Modules when Changed on Disk
Synopsis
# Monitor and reload all modules in %INC:
# httpd.conf:
PerlModule Apache::Reload
PerlInitHandler Apache::Reload
# Reload groups of modules:
# httpd.conf:
PerlModule Apache::Reload
PerlInitHandler Apache::Reload
PerlSetVar ReloadAll Off
PerlSetVar ReloadModules "ModPerl::* Apache::*"
#PerlSetVar ReloadDebug On
# Reload a single module from within itself:
package My::Apache::Module;
use Apache::Reload;
sub handler { ... }
1;
Description
"Apache::Reload" reloads modules that change on the disk.
When Perl pulls a file via "require", it stores the filename in the
global hash %INC. The next time Perl tries to "require" the same file,
it sees the file in %INC and does not reload from disk. This module's
handler can be configured to iterate over the modules in %INC and
reload those that have changed on disk or only specific modules that
have registered themselves with "Apache::Reload". It can also do the
check for modified modules, when a special touch-file has been modi-
fied.
Note that "Apache::Reload" operates on the current context of @INC.
Which means, when called as a "Perl*Handler" it will not see @INC paths
added or removed by "Apache::Registry" scripts, as the value of @INC is
saved on server startup and restored to that value after each request.
In other words, if you want "Apache::Reload" to work with modules that
live in custom @INC paths, you should modify @INC when the server is
started. Besides, 'use lib' in the startup script, you can also set
the "PERL5LIB" variable in the httpd's environment to include any non-
standard 'lib' directories that you choose. For example, to accomplish
that you can include a line:
PERL5LIB=/home/httpd/perl/extra; export PERL5LIB
in the script that starts Apache. Alternatively, you can set this envi-
ronment variable in httpd.conf:
PerlSetEnv PERL5LIB /home/httpd/perl/extra
Monitor All Modules in %INC
To monitor and reload all modules in %INC, simply add the following
configuration to your httpd.conf:
PerlModule Apache::Reload
PerlInitHandler Apache::Reload
Register Modules Implicitly
To only reload modules that have registered with "Apache::Reload", add
the following to the httpd.conf:
PerlModule Apache::Reload
PerlInitHandler Apache::Reload
PerlSetVar ReloadAll Off
# ReloadAll defaults to On
Then any modules with the line:
use Apache::Reload;
Will be reloaded when they change.
Register Modules Explicitly
You can also register modules explicitly in your httpd.conf file that
you want to be reloaded on change:
PerlModule Apache::Reload
PerlInitHandler Apache::Reload
PerlSetVar ReloadAll Off
PerlSetVar ReloadModules "My::Foo My::Bar Foo::Bar::Test"
Note that these are split on whitespace, but the module list must be in
quotes, otherwise Apache tries to parse the parameter list.
The "*" wild character can be used to register groups of files under
the same namespace. For example the setting:
PerlSetVar ReloadModules "ModPerl::* Apache::*"
will monitor all modules under the namespaces "ModPerl::" and
"Apache::".
Special "Touch" File
You can also declare a file, which when gets touch(1)ed, causes the
reloads to be performed. For example if you set:
PerlSetVar ReloadTouchFile /tmp/reload_modules
and don't touch(1) the file /tmp/reload_modules, the reloads won't hap-
pen until you go to the command line and type:
% touch /tmp/reload_modules
When you do that, the modules that have been changed, will be magically
reloaded on the next request. This option works with any mode described
before.
Performance Issues
This modules is perfectly suited for a development environment. Though
it's possible that you would like to use it in a production environ-
ment, since with "Apache::Reload" you don't have to restart the server
in order to reload changed modules during software updates. Though this
convenience comes at a price:
o If the "touch" file feature is used, "Apache::Reload" has to
stat(2) the touch file on each request, which adds a slight but
most likely insignificant overhead to response times. Otherwise
"Apache::Reload" will stat(2) each registered module or even
worse--all modules in %INC, which will significantly slow every-
thing down.
o Once the child process reloads the modules, the memory used by
these modules is not shared with the parent process anymore. There-
fore the memory consumption may grow significantly.
Therefore doing a full server stop and restart is probably a better
solution.
Debug
If you aren't sure whether the modules that are supposed to be
reloaded, are actually getting reloaded, turn the debug mode on:
PerlSetVar ReloadDebug On
Threaded MPM and Multiple Perl Interpreters
If you use "Apache::Reload" with a threaded MPM and multiple Perl
interpreters, the modules will be reloaded by each interpreter as they
are used, not every interpreters at once. Similar to mod_perl 1.x
where each child has its own Perl interpreter, the modules are reloaded
as each child is hit with a request.
If a module is loaded at startup, the syntax tree of each subroutine is
shared between interpreters (big win), but each subroutine has its own
padlist (where lexical my variables are stored). Once "Apache::Reload"
reloads a module, this sharing goes away and each Perl interpreter will
have its own copy of the syntax tree for the reloaded subroutines.
Pseudo-hashes
The short summary of this is: Don't use pseudo-hashes. They are depre-
cated since Perl 5.8 and will be removed in 5.10
Use an array with constant indexes. Its faster in the general case, its
more guaranteed, and generally, it works.
The long summary is that some work has been done to get this module
working with modules that use pseudo-hashes, but it's still broken in
the case of a single module that contains multiple packages that all
use pseudo-hashes.
So don't do that.
Authors
Matt Sergeant, matt@sergeant.org
Stas Bekman (porting to mod_perl 2.0)
A few concepts borrowed from "Stonehenge::Reload" by Randal Schwartz
and "Apache::StatINC" (mod_perl 1.x) by Doug MacEachern and Ask Bjoern
Hansen.
See Also
"Stonehenge::Reload"
perl v5.8.0 2002-06-15 RELOAD(1)
