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<!--
$FML: bootloader.sgml,v 1.1 2005/07/27 12:21:35 fukachan Exp $
-->
<chapter id="bootloader">
<title>
&fml8; Boot Loader To Resolve Version Dependence Dynamically
</title>
<para>
&fml8; provides a boot loader to resolve version dependence
dynamically. For example, the loader boot straps &fml8; as follows:
<screen>
fml (libexec/distribute) boots like this ...
functions class
----------------------------------------
main::Bootstrap() libexec/loader
|
V
main::Bootstrap2() FML::Process::Switch
|
V
ProcessSwitch() FML::Process::Switch
|
|
| switch to ($obj = FML::Process:Distribute)
|
V
ProcessStart($obj,$args) FML::Process::Flow
</screen>
</para>
<sect1 id="bootloader.example.distribute">
<title>
Case: Distribution
</title>
<para>
&fml8; loader boot straps like this in the case of distribution.
</para>
<para>
/usr/local/libexec/fml/distributre (is same as
/usr/local/libexec/fml/loader in fact) reads
/usr/local/etc/fml/main.cf and resolvers the version it should use
from $fml_version variable. Let $fml_version current-20010501. The
loader uses library perl modules under
/usr/local/lib/fml/current-20010501/.
</para>
<para>
The loader resets @INC (perl include path).
It loads FML::Process::Switch and checks $0 (program name in process table).
The loader resolves from the name that the role is distribution.
It loads FML::Process::Distribute and switches to the class.
</para>
<para>
The relation between program name and class (perl module) is defined
at /usr/local/etc/fml/defaults/$fml_version/modules file.
</para>
<para>
FML::Process::Flow::ProcessStart() function drives these sequential
steps. ProcessStart() takes FML::Process::Distribute object as an
argument and drives the object.
</para>
</sect1>
<sect1 id="bootloader.classes">
<title>
FML::Process:: Class Structure
</title>
<para>
<screen>
FML::Process::Distribute >-|
FML::Process::Command >-|-- FML::Process::Kernel
FML::Process::Mead >-| |
|-use-a FML::Parse
|-use-a FML::Config
|-use-a FML::Log
|-use-a ... SOMETHING ...
</screen>
</para>
</sect1>
<sect1 id="bootloader.classes2">
<title>
Modules In Process Execution
</title>
<itemizedlist>
<listitem>
<para>
libexec/loader (wrapper):
executes Bootstrap() runction.
libexec/distribute et.al. is a symlink(2) to this loader.
See under /usr/local/libexec/fml/ path.
</para>
</listitem>
<listitem>
<itemizedlist>
<listitem>
<para>
reads /usr/local/etc/fml/main.cf and resolves $fml_version.
reset @INC by main.cf value.
Since default_config.cf is version dependent,
the loader should evaluate the file before it reads
ML specific configuration files.
</para>
</listitem>
<listitem>
<para>
Evaluate @ARGV and resolves which ML specific configuration
files we need to load.
</para>
</listitem>
<listitem>
<para>
load FML::Process::Switch class which is also version dependent.
</para>
<itemizedlist>
<listitem>
<para>
The loader executes Bootstrap2() and ProcessSwitch()
to switch the context to each one such as
distribution, command mail et.al.
In this time, the loader knows the role
from $0 process name.
</para>
</listitem>
<listitem>
<para>
Exapmle of Polymorphyism:
dynamic binding of module and creation of process
object in starting the process.
FML::Process::Flow describes the flow of process
like this:
<screen>
$process = new FML::Process::SOMETHING;
$process->prepare($args);
$process->verify_request($args);
$process->run($args);
$process->finish($args);
</screen>
Each process should probide proper methods under
FML::Process:: class.
</para>
</listitem>
</itemizedlist>
</listitem>
</itemizedlist>
</listitem>
</itemizedlist>
</sect1>
<sect1 id="bootloader.resolv.mlxxx">
<title>
Discussion: Where Function Should Resolve $ml_name And $ml_domain.
</title>
<para>
Currently &fml8; resolves them in prepare() under FML::Process:: classes.
</para>
<para>
Here is a part of background idea.
<screen>
main::Bootstrap()
resoles $fml_version based on main.cf information.
pass hints to some processes e.g. CGI.
CGI only
it should ignore invalid input.
$ml_name $and ml_domain is hard-coded in cgi scripts.
main::Bootstrap2()
ProcessSwitch()
resolves the module, configuration files, library path and @INC.
pass hints to some processes e.g. CGI.
CGI only
ProcessStart($obj, $args)
main process starts
new
prepare
resoles $ml_name and $ml_domain.
parse input from CGI using hints.
determine ml specific configuration files.
parse incoming message.
parse command line arguments.
</screen>
</para>
</sect1>
</chapter>
|
