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%INC
Apache2::Reload - Reload Perl Modules when Changed on Disk
# Monitor and reload all modules in %INC: # httpd.conf: PerlModule Apache2::Reload PerlInitHandler Apache2::Reload
# when working with protocols and connection filters # PerlPreConnectionHandler Apache2::Reload
# Reload groups of modules:
# httpd.conf:
PerlModule Apache2::Reload
PerlInitHandler Apache2::Reload
PerlSetVar ReloadAll Off
PerlSetVar ReloadModules "ModPerl::* Apache2::*"
#PerlSetVar ReloadDebug On
# Reload a single module from within itself:
package My::Apache2::Module;
use Apache2::Reload;
sub handler { ... }
1;
Apache2::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 Apache2::Reload. It can
also do the check for modified modules, when a special touch-file has
been modified.
Note that Apache2::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 ModPerl::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
Apache2::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 environment variable in httpd.conf:
PerlSetEnv PERL5LIB /home/httpd/perl/extra
%INCTo monitor and reload all modules in %INC at the beginning of
request's processing, simply add the following configuration to your
httpd.conf:
PerlModule Apache2::Reload PerlInitHandler Apache2::Reload
When working with connection filters and protocol modules
Apache2::Reload should be invoked in the pre_connection stage:
PerlPreConnectionHandler Apache2::Reload
See also the discussion on
PerlPreConnectionHandler|docs::2.0::user::handlers::protocols/PerlPreConnectionHandler.
To only reload modules that have registered with Apache2::Reload,
add the following to the httpd.conf:
PerlModule Apache2::Reload PerlInitHandler Apache2::Reload PerlSetVar ReloadAll Off # ReloadAll defaults to On
Then any modules with the line:
use Apache2::Reload;
Will be reloaded when they change.
You can also register modules explicitly in your httpd.conf file that you want to be reloaded on change:
PerlModule Apache2::Reload PerlInitHandler Apache2::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::* Apache2::*"
will monitor all modules under the namespaces ModPerl:: and
Apache2::.
To reload modules only in certain directories (and their subdirectories) add the following to the httpd.conf:
PerlModule Apache2::Reload PerlInitHandler Apache2::Reload PerlSetVar ReloadDirectories "/tmp/project1 /tmp/project2"
You can further narrow the list of modules to be reloaded from the
chosen directories with ReloadModules as in:
PerlModule Apache2::Reload PerlInitHandler Apache2::Reload PerlSetVar ReloadDirectories "/tmp/project1 /tmp/project2" PerlSetVar ReloadAll Off PerlSetVar ReloadModules "MyApache2::*"
In this configuration example only modules from the namespace
MyApache2:: found in the directories /tmp/project1/ and
/tmp/project2/ (and their subdirectories) will be reloaded.
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 happen 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.
In some cases, it might be necessary to explicitely stop reloading a module.
Apache2::Reload->unregister_module('Some::Module');
But be carefull, since unregistering a module in this way will only do so for the current interpreter. This feature should be used with care.
This module is perfectly suited for a development environment. Though
it's possible that you would like to use it in a production
environment, since with Apache2::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:
If the ``touch'' file feature is used, Apache2::Reload has to stat(2)
the touch file on each request, which adds a slight but most likely
insignificant overhead to response times. Otherwise Apache2::Reload
will stat(2) each registered module or even worse--all modules in
%INC, which will significantly slow everything down.
Once the child process reloads the modules, the memory used by these modules is not shared with the parent process anymore. Therefore the memory consumption may grow significantly.
Therefore doing a full server stop and restart is probably a better solution.
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
If you modify modules, which don't declare their package, and rely on
Apache2::Reload to reload them, you may encounter problems: i.e.,
it'll appear as if the module wasn't reloaded when in fact it
was. This happens because when Apache2::Reload require()s such a
module all the global symbols end up in the Apache2::Reload
namespace! So the module does get reloaded and you see the compile
time errors if there are any, but the symbols don't get imported to
the right namespace. Therefore the old version of the code is running.
Apache2::Reload uses %INC to find the files on the filesystem. If
an entry for a certain filepath in %INC is relative,
Apache2::Reload will use @INC to try to resolve that relative
path. Now remember that mod_perl freezes the value of @INC at the
server startup, and you can modify it only for the duration of one
request when you need to load some module which is not in on of the
@INC directories. So a module gets loaded, and registered in
%INC with a relative path. Now when Apache2::Reload tries to find
that module to check whether it has been modified, it can't find since
its directory is not in @INC. So Apache2::Reload will silently
skip that module.
You can enable the Debug|/Debug mode to see what Apache2::Reload
does behind the scenes.
The following problem is relevant only to registry handlers that cache
the compiled script. For example it concerns
ModPerl::Registry|docs::2.0::api::ModPerl::Registry but not
ModPerl::PerlRun|docs::2.0::api::ModPerl::PerlRun.
Let's say that there is a module My::Utils:
#file:My/Utils.pm
#----------------
package My::Utils;
BEGIN { warn __PACKAGE__ , " was reloaded\n" }
use base qw(Exporter);
@EXPORT = qw(colour);
sub colour { "white" }
1;
And a registry script test.pl:
#file:test.pl #------------ use My::Utils; print "Content-type: text/plain\n\n"; print "the color is " . colour();
Assuming that the server is running in a single mode, we request the script for the first time and we get the response:
the color is white
Now we change My/Utils.pm:
- sub colour { "white" }
+ sub colour { "red" }
And issue the request again. Apache2::Reload does its job and we can
see that My::Utils was reloaded (look in the error_log
file). However the script still returns:
the color is white
Even though My/Utils.pm was reloaded, ModPerl::Registry's cached
code won't run 'use My::Utils;' again (since it happens only once,
i.e. during the compile time). Therefore the script doesn't know that
the subroutine reference has been changed.
This is easy to verify. Let's change the script to be:
#file:test.pl #------------ use My::Utils; print "Content-type: text/plain\n\n"; my $sub_int = \&colour; my $sub_ext = \&My::Utils::colour; print "int $sub_int\n"; print "ext $sub_ext\n";
Issue a request, you will see something similar to:
int CODE(0x8510af8) ext CODE(0x8510af8)
As you can see both point to the same CODE reference (meaning that it's the same symbol). After modifying My/Utils.pm again:
- sub colour { "red" }
+ sub colour { "blue" }
and calling the script on the secondnd time, we get:
int CODE(0x8510af8) ext CODE(0x851112c)
You can see that the internal CODE reference is not the same as the external one.
There are two solutions to this problem:
Solution 1: replace use() with an explicit require() +
import().
- use My::Utils; + require My::Utils; My::Utils->import();
now the changed functions will be reimported on every request.
Solution 2: remember to touch the script itself every time you change the module that it requires.
If you use Apache2::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 1.0
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
Apache2::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.
The short summary of this is: Don't use pseudo-hashes. They are deprecated since Perl 5.8 and are removed in 5.9.
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.
mod_perl 2.0 and its core modules are copyrighted under The Apache Software License, Version 2.0.
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.