=head1 NAME Apache::Reload - Reload Perl Modules when Changed on Disk =head1 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; =head1 Description C<Apache::Reload> reloads modules that change on the disk. When Perl pulls a file via C<require>, it stores the filename in the global hash C<%INC>. The next time Perl tries to C<require> the same file, it sees the file in C<%INC> and does not reload from disk. This module's handler can be configured to iterate over the modules in C<%INC> and reload those that have changed on disk or only specific modules that have registered themselves with C<Apache::Reload>. It can also do the check for modified modules, when a special touch-file has been modified. Note that C<Apache::Reload> operates on the current context of C<@INC>. Which means, when called as a C<Perl*Handler> it will not see C<@INC> paths added or removed by C<Apache::Registry> scripts, as the value of C<@INC> is saved on server startup and restored to that value after each request. In other words, if you want C<Apache::Reload> to work with modules that live in custom C<@INC> paths, you should modify C<@INC> when the server is started. Besides, C<'use lib'> in the startup script, you can also set the C<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 I<httpd.conf>: PerlSetEnv PERL5LIB /home/httpd/perl/extra =head2 Monitor All Modules in C<%INC> To monitor and reload all modules in C<%INC>, simply add the following configuration to your I<httpd.conf>: PerlModule Apache::Reload PerlInitHandler Apache::Reload =head2 Register Modules Implicitly To only reload modules that have registered with C<Apache::Reload>, add the following to the I<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. =head2 Register Modules Explicitly You can also register modules explicitly in your I<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 B<must> be in quotes, otherwise Apache tries to parse the parameter list. The C<*> 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 C<ModPerl::> and C<Apache::>. =head2 Monitor Only Certain Sub Directories To reload modules only in certain directories (and their subdirectories) add the following to the I<httpd.conf>: PerlModule Apache::Reload PerlInitHandler Apache::Reload PerlSetVar ReloadDirectories "/tmp/project1 /tmp/project2" You can further narrow the list of modules to be reloaded from the chosen directories with C<ReloadModules> as in: PerlModule Apache::Reload PerlInitHandler Apache::Reload PerlSetVar ReloadDirectories "/tmp/project1 /tmp/project2" PerlSetVar ReloadAll Off PerlSetVar ReloadModules "MyApache::*" In this configuration example only modules from the namespace C<MyApache::> found in the directories I</tmp/project1/> and I</tmp/project2/> (and their subdirectories) will be reloaded. =head2 Special "Touch" File You can also declare a file, which when gets C<touch(1)>ed, causes the reloads to be performed. For example if you set: PerlSetVar ReloadTouchFile /tmp/reload_modules and don't C<touch(1)> the file I</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. =head1 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 environment, since with C<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: =over =item * If the "touch" file feature is used, C<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 C<Apache::Reload> will stat(2) each registered module or even worse--all modules in C<%INC>, which will significantly slow everything down. =item * 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. =back Therefore doing a full server stop and restart is probably a better solution. =head1 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 =head1 Problems With Reloading Modules Which Do Not Declare Their Package Name If you modify modules which don't declare their C<package> and rely on C<Apache::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 C<Apache::Reload> C<require()>s such a module all the global symbols end up in the C<Apache::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. =head1 Threaded MPM and Multiple Perl Interpreters If you use C<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 1.0 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 C<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. =head1 Pseudo-hashes 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. =head1 Authors Matt Sergeant, matt@sergeant.org Stas Bekman (porting to mod_perl 2.0) A few concepts borrowed from C<Stonehenge::Reload> by Randal Schwartz and C<Apache::StatINC> (mod_perl 1.x) by Doug MacEachern and Ask Bjoern Hansen. =head1 See Also C<Stonehenge::Reload> =cut