preload-forms

Arguments:

This macro can be used to create a fasl file with CLOS optimizations, as we describe.

A generic function examines its arguments to determine which method or methods are applicable. This is called discrimination. The symbol-function of a generic-function is a discriminator function. There are various kinds of discriminators and the discriminator for a particular generic function may change during the execution of a program.

When Lisp determines that a generic function needs a different kind of discriminator it checks to see if the one it needs has already been built and, if not, creates one. The creation of a discriminator is relatively expensive since it involves the Lisp compiler.

When a CLOS application is loaded the generic-functions all have a simple discriminator which will select the correct discriminator when the generic function is first called. Therefore when a CLOS application starts it will run very slowly unless the discriminators it needs are already built. The only way to tell which discriminators your program needs is to run your program for a while and then look at the list of discriminators that exist. Allegro CL provides a mechanism for dumping out these discriminators and then loading them in with your program so that when the program starts all the discriminators it will need will already exist.

Further, with method-combination a call to a generic function can result in a sequence of methods being called. The code that calls the methods and processes the results of each call is called an effective method. In order to make effective methods fast, Lisp compiles them. In order to cut down on the compilation cost, Lisp actually creates effective-method templates which are functions closed over the particular methods to be called.

Thus many effective methods can share the same code. Just as in the case of discriminators discussed above, it is expensive to start a CLOS application running if the effective methods it will need haven't been compiled already. And again Allegro CL provides a way of saving the effective methods that the application has used so that they can be defined before the application starts.

You can dump discriminator functions and effective methods to a fasl file by compiling a source file that contains the following two lines after loading and running your application:

(in-package :clos) (preload-forms)

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This page was not revised from the 8.2 page.
Created 2012.5.30.