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<!--
$FML: lock.sgml,v 1.1 2005/07/27 12:21:36 fukachan Exp $
-->
<chapter id="lock">
<title>
Lock
</title>
<para>
Synchronization among processes uses lock.
&fml8; provides flock(2) or lockf(2) based lock mechanism.
</para>
<sect1 id="lock.overview">
<title>
Overview: Lock
</title>
<para>
After 2003/03, &fml8; provides more granular not giant lock.
</para>
<para>
Each resource defines each lock channel name.
</para>
<para>
For example,
Mail::Delivery related class accesses the member list.
It needs several locks.
</para>
<para>
Mail::Delivery::SMTP needs lock of member list.
FML::Send and FML::Process::Delivery locks member list access
in callling Mail::Delivery::SMTP.
</para>
<para>
Instead
Mail::Delivery::Queue just sees the mail queue.
The function can access the queue concurrently, also.
So this module does not need lock.
</para>
<para>
Generally speaking, modules using maps require lock.
For example,
FML/Command/UserControl.pm and
FML/Command/Auth.pm
needs write lock, but
FML/Credential.pm
needs only read lock.
</para>
<para>
It is useful if &fml8; provides reader writer lock. But it is not implemented.
Currently we attension we use short critical region.
</para>
</sect1>
<sect1 id="lock.todo">
<title>
TODO
</title>
<para>
Mutex lock in calling *_maps.
</para>
<para>
READER WRITER LOCK in calling IO::Adapter.
</para>
</sect1>
</chapter>
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