NAME¶
ModPerl::MethodLookup -- Lookup mod_perl modules, objects and methods
Synopsis¶
use ModPerl::MethodLookup;
# return all module names containing XS method 'print'
my ($hint, @modules) =
ModPerl::MethodLookup::lookup_method('print');
# return only module names containing method 'print' which
# expects the first argument to be of type 'Apache2::Filter'
# (here $filter is an Apache2::Filter object)
my ($hint, @modules) =
ModPerl::MethodLookup::lookup_method('print', $filter);
# or
my ($hint, @modules) =
ModPerl::MethodLookup::lookup_method('print', 'Apache2::Filter');
# what XS methods defined by module 'Apache2::Filter'
my ($hint, @methods) =
ModPerl::MethodLookup::lookup_module('Apache2::Filter');
# what XS methods can be invoked on the object $r (or a ref)
my ($hint, @methods) =
ModPerl::MethodLookup::lookup_object($r);
# or
my ($hint, @methods) =
ModPerl::MethodLookup::lookup_object('Apache2::RequestRec');
# preload all mp2 modules in startup.pl
ModPerl::MethodLookup::preload_all_modules();
# command line shortcuts
% perl -MModPerl::MethodLookup -e print_module \
Apache2::RequestRec Apache2::Filter
% perl -MModPerl::MethodLookup -e print_object Apache2
% perl -MModPerl::MethodLookup -e print_method \
get_server_built request
% perl -MModPerl::MethodLookup -e print_method read
% perl -MModPerl::MethodLookup -e print_method read APR::Bucket
Description¶
mod_perl 2.0 provides many methods, which reside in various modules. One has to
load each of the modules before using the desired methods.
"ModPerl::MethodLookup" provides the Perl API for finding module
names which contain methods in question and other helper functions, to find
out out what methods defined by some module, what methods can be called on a
given object, etc.
API¶
"lookup_method()"¶
Find modules (packages) containing a certain method
($hint, @modules) = lookup_method($method_name);
($hint, @modules) = lookup_method($method_name, $object);
($hint, @modules) = lookup_method($method_name, $class));
- arg1: $method_name ( string )
- the method name to look up
- opt arg2: $object or $class
- a blessed object or the name of the class it's blessed
into. If there is more than one match, this extra information is used to
return only modules containing methods operating on the objects of the
same kind.
If a sub-classed object is passed it'll be handled correctly, by checking
its super-class(es). This usage is useful when the "AUTOLOAD" is
used to find a not yet loaded module which include the called method.
- ret1: $hint
- a string containing a human readable lookup result,
suggesting which modules should be loaded, ready for copy-n-paste or
explaining the failure if the lookup didn't succeed.
- ret2: @modules
- an array of modules which have matched the query, i.e. the
names of the modules which contain the requested method.
- since: 2.0.00
Examples:
Return all module names containing XS method
print:
my ($hint, @modules) =
ModPerl::MethodLookup::lookup_method('print');
Return only module names containing method
print which expects the first
argument to be of type "Apache2::Filter":
my $filter = bless {}, 'Apache2::Filter';
my ($hint, @modules) =
ModPerl::MethodLookup::lookup_method('print', $filter);
or:
my ($hint, @modules) =
ModPerl::MethodLookup::lookup_method('print', 'Apache2::Filter');
"lookup_module()"¶
Find methods contained in a certain module (package)
($hint, @methods) = lookup_module($module_name);
- arg1: $module_name ( string )
- the module name
- ret1: $hint
- a string containing a human readable lookup result,
suggesting, which methods the module $module_name implements, or
explaining the failure if the lookup failed.
- ret2: @methods
- an array of methods which have matched the query, i.e. the
names of the methods defined in the requested module.
- since: 2.0.00
Example:
What XS methods defined by module "Apache2::Filter":
my ($hint, @methods) =
ModPerl::MethodLookup::lookup_module('Apache2::Filter');
"lookup_object()"¶
($hint, @methods) = lookup_object($object);
($hint, @methods) = lookup_object($class);
- arg1: $object or $class
- an object or a name of a class an object is blessed into
If a sub-classed object is passed it'll be handled correctly, by including
methods provided by its super-class(es).
- ret1: $hint
- a string containing a human readable lookup result,
suggesting, which methods the given object can invoke (including module
names that need to be loaded to use those methods), or explaining the
failure if the lookup failed.
- ret2: @methods
- an array of methods which have matched the query, i.e. the
names of the methods that can be invoked on the given object (or its class
name).
- since: 2.0.00
META: As of this writing this function may miss some of the functions/methods
that can be invoked on the given object. Currently we can't programmatically
deduct the objects they are invoked on, because these methods are written in
pure XS and manipulate the arguments stack themselves. Currently these are
mainly XS functions, not methods, which of course aren't invoked on objects.
There are also logging function wrappers ("Apache2::Log").
Examples:
What XS methods can be invoked on the object $r:
my ($hint, @methods) =
ModPerl::MethodLookup::lookup_object($r);
or $r's class -- "Apache2::RequestRec":
my ($hint, @methods) =
ModPerl::MethodLookup::lookup_object('Apache2::RequestRec');
"preload_all_modules()"¶
The function "preload_all_modules()" preloads all mod_perl 2.0
modules, which implement their API in XS. This is similar to the mod_perl 1.0
behavior which has most of its methods loaded at the startup.
CPAN modules developers should make sure their distribution loads each of the
used mod_perl 2.0 modules explicitly, and not use this function, as it takes
the fine control away from the users. One should avoid doing this the
production server (unless all modules are used indeed) in order to save
memory.
- since: 2.0.00
"print_method()"¶
"print_method()" is a convenience wrapper for
"lookup_method()", mainly designed to be used from the command line.
For example to print all the modules which define method
read execute:
% perl -MModPerl::MethodLookup -e print_method read
Since this will return more than one module, we can narrow the query to only
those methods which expect the first argument to be blessed into class
"APR::Bucket":
% perl -MModPerl::MethodLookup -e print_method read APR::Bucket
You can pass more than one method and it'll perform a lookup on each of the
methods. For example to lookup methods "get_server_built" and
"request" you can do:
% perl -MModPerl::MethodLookup -e print_method \
get_server_built request
The function "print_method()" is exported by default.
- since: 2.0.00
"print_module()"¶
"print_module()" is a convenience wrapper for
"lookup_module()", mainly designed to be used from the command line.
For example to print all the methods defined in the module
"Apache2::RequestRec", followed by methods defined in the module
"Apache2::Filter" you can run:
% perl -MModPerl::MethodLookup -e print_module \
Apache2::RequestRec Apache2::Filter
The function "print_module()" is exported by default.
- since: 2.0.00
"print_object()"¶
"print_object()" is a convenience wrapper for
"lookup_object()", mainly designed to be used from the command line.
For example to print all the methods that can be invoked on object blessed
into a class "Apache2::RequestRec" run:
% perl -MModPerl::MethodLookup -e print_object \
Apache2::RequestRec
Similar to "print_object()", more than one class can be passed to this
function.
The function "print_object()" is exported by default.
- since: 2.0.00
Applications¶
"AUTOLOAD"¶
When Perl fails to locate a method it checks whether the package the object
belongs to has an "AUTOLOAD" function defined and if so, calls it
with the same arguments as the missing method while setting a global variable
$AUTOLOAD (in that package) to the name of the originally called method. We
can use this facility to lookup the modules to be loaded when such a failure
occurs. Though since we have many packages to take care of we will use a
special "UNIVERSAL::AUTOLOAD" function which Perl calls if can't
find the "AUTOLOAD" function in the given package.
In that function you can query "ModPerl::MethodLookup",
require() the module that includes the called method and call that
method again using the
goto() trick:
use ModPerl::MethodLookup;
sub UNIVERSAL::AUTOLOAD {
my ($hint, @modules) =
ModPerl::MethodLookup::lookup_method($UNIVERSAL::AUTOLOAD, @_);
if (@modules) {
eval "require $_" for @modules;
goto &$UNIVERSAL::AUTOLOAD;
}
else {
die $hint;
}
}
However we don't endorse this approach. It's a better approach to always abort
the execution which printing the $hintand use fix the code to load the missing
module. Moreover installing "UNIVERSAL::AUTOLOAD" may cause a lot of
problems, since once it's installed Perl will call it every time some method
is missing (e.g. undefined "DESTROY" methods). The following
approach seems to somewhat work for me. It installs
"UNIVERSAL::AUTOLOAD" only when the the child process starts.
httpd.conf:
-----------
PerlChildInitHandler ModPerl::MethodLookupAuto
startup.pl:
-----------
{
package ModPerl::MethodLookupAuto;
use ModPerl::MethodLookup;
use Carp;
sub handler {
*UNIVERSAL::AUTOLOAD = sub {
my $method = $AUTOLOAD;
return if $method =~ /DESTROY/; # exclude DESTROY resolving
my ($hint, @modules) =
ModPerl::MethodLookup::lookup_method($method, @_);
$hint ||= "Can't find method $AUTOLOAD";
croak $hint;
};
return 0;
}
}
This example doesn't load the modules for you. It'll print to STDERR what module
should be loaded, when a method from the not-yet-loaded module is called.
A similar technique is used by "Apache2::porting".
META: there is a better version of AUTOLOAD discussed on the dev list. Replace
the current one with it. (search the archive for EazyLife)
Command Line Lookups¶
When a method is used and mod_perl has reported a failure to find it, it's often
useful to use the command line query to figure out which module needs to be
loaded. For example if when executing:
$r->construct_url();
mod_perl complains:
Can't locate object method "construct_url" via package
"Apache2::RequestRec" at ...
you can ask "ModPerl::MethodLookup" for help:
% perl -MModPerl::MethodLookup -e print_method construct_url
To use method 'construct_url' add:
use Apache2::URI ();
and after copy-n-pasting the use statement in our code, the problem goes away.
One can create a handy alias for this technique. For example, C-style shell
users can do:
% alias lookup "perl -MModPerl::MethodLookup -e print_method"
For Bash-style shell users:
% alias lookup="perl -MModPerl::MethodLookup -e print_method"
Now the lookup is even easier:
% lookup construct_url
to use method 'construct_url' add:
use Apache2::URI;
Similar aliases can be provided for "print_object()" and
"print_module()".
Todo¶
These methods aren't yet picked by this module (the extract from the map file):
modperl_filter_attributes | MODIFY_CODE_ATTRIBUTES
modperl_spawn_proc_prog | spawn_proc_prog
apr_ipsubnet_create | new
Please report to the mod_perl development mailing list if you find any other
missing methods. But remember that as of this moment the module reports only
XS functions. In the future we may add support for pure perl functions/methods
as well.
See Also¶
- •
- the mod_perl 1.0 backward compatibility document
- •
- porting Perl modules
- •
- porting XS modules
- •
- "Apache2::porting"
Copyright¶
mod_perl 2.0 and its core modules are copyrighted under The Apache Software
License, Version 2.0.
Authors¶
The mod_perl development team and numerous contributors.