bird/lib/resource.sgml

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	BIRD Programmer's Guide: Resources

	(c) 2000 Martin Mares <mj@ucw.cz>
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<chapt>Resources

<sect>Introduction

<p>Most large software projects implemented in classical procedural
programming languages usually end up with lots of code taking care
of resource allocation and deallocation. Bugs in such code are often
very difficult to find, because they cause only `resource leakage',
that is keeping a lot of memory and other resources which nobody
references to.

<p>We've tried to solve this problem by employing a resource tracking
system which keeps track of all the resources allocated by all the
modules of BIRD, deallocates everything automatically when a module
shuts down and it's is able to print out the list of resources and
the corresponding modules they are allocated by.

<p>Each allocated resource (and from now we'll speak about allocated
resources only) is represented by a structure starting with a standard
header (struct <struct/resource/) consisting of a list node (resources are
often linked to various lists) and a pointer to <struct/resclass/ -- a resource
class structure pointing to functions implementing generic resource
operations (such as freeing of the resource) for the particular resource
type.

<p>There exist the following types of resources:

<itemize>
<item><it/Resource pools/ (<struct/pool/)
<item><it/Memory blocks/
<item><it/Linear memory pools/ (<struct/linpool/)
<item><it/Slabs/ (<struct/slab/)
<item><it/Events/ (<struct/event/) 
<item><it/Timers/ (<struct/timer/) 
<item><it/Sockets/ (<struct/socket/) 
</itemize>