/ 
Mail-Box-2.022
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/ Mail::Box::Locker

NAME

Mail::Box::Locker - manage the locking of mail folders

CLASS INHERITANCE

Mail::Box::Locker is a Mail::Reporter

Mail::Box::Locker is extended by Mail::Box::Locker::DotLock Mail::Box::Locker::Flock Mail::Box::Locker::Multi Mail::Box::Locker::NFS Mail::Box::Locker::POSIX

SYNOPSIS

use Mail::Box::Locker;
my $locker = new Mail::Box::Locker(folder => $folder);

$locker->lock;
$locker->isLocked;
$locker->hasLock;
$locker->unlock;

use Mail::Box;
my $folder = Mail::Box->new(lock_method => 'DOTLOCK');
print $folder->locker->type;

DESCRIPTION

Each Mail::Box will create its own Mail::Box::Locker object which will handle the locking for it. You can access of the object directly from the folder, as shown in the examples below.

METHODS

Initiation

new OPTIONS

Create a new lock. You may do this directly. However, in most cases the lock will not be separately instantiated but will be the second class in a multiple inheritance construction with a Mail::Box.

Generally the client program specifies the locking behavior through options given to the folder class.

OPTION               DEFAULT
expires              1 hour
file                 undef
folder               <obligatory>
log                  'WARNINGS'
method               'DOTLOCK'
timeout              10 seconds
trace                'WARNINGS'
expires => SECONDS

How long can a lock exist? If a different e-mail program leaves a stale lock, then this lock will be removed automatically after the specified number of seconds.

file => FILENAME

Name of the file to lock, or the name of the lockfile (depends on the kind of lock used).

folder => FOLDER

Which folder is locked.

log => LEVEL

See Mail::Reporter::new(log)

method => METHOD | CLASS

Which kind of locking, specified as one of the following names, or a full CLASS name. Supported METHODs are

'DOTLOCK' | 'dotlock'

The folder handler creates a file which signals that it is in use. This is a bit problematic, because not all mail-handling software agree on the name of the file to be created.

On various folder types, the lockfile differs. See the documentation for each folder, which describes the locking strategy as well as special options to change the default behavior.

'FLOCK' | 'flock'

For some folder handlers, locking is based on a file locking mechanism provided by the operating system. However, this does not work on all systems, such as network filesystems, and such. This also doesn't work on folders based on directories (Mail::Box::Dir and derived).

'POSIX' | 'posix'

Use the POSIX standard fcntl locking.

'MULTI' | 'multi'

Try more than one locking method to be used at the same time, probably all available, to avoid any chance that you miss a lock from a different application.

'NFS' | 'nfs'

A kind of dotlock file-locking mechanism, but adapted to work over NFS. Extra precaution is needed because an open O_EXCL on NFS is not an atomic action.

'NONE' | 'none'

Do not use locking.

The other option is to produce your own Mail::Box::Locker derived class, which implements the desired locking method. (Please consider offering it for inclusion in the public Mail::Box module!) Create an instance of that class with this parameter:

my $locker = Mail::Box::Locker::MyOwn->new;
$folder->open(locker => $locker);
timeout => SECONDS|'NOTIMEOUT'

How long to wait while trying to acquire the lock. The lock request will fail when the specified number of seconds is reached. If 'NOTIMEOUT' is specified, the module will wait until the lock can be taken.

Whether it is possible to limit the wait time is platform- and locking-method-specific. For instance, the `dotlock' method on Windows will always wait until the lock has been received.

trace => LEVEL

See Mail::Reporter::new(trace)

The Locker

DESTROY

When the locker is destroyed, for instance when the folder is closed or the program ends, the lock will be automatically removed.

filename

Returns the filename which is used to lock the folder. How this file is used depends on the locking method.

Examples:

print $locker->filename;
print $folder->lockFilename;
name

Returns the method used to lock the folder. See the new() method for details on how to specify the lock method. The name of the method is returned in uppercase.

Examples:

if($locker->name eq 'FLOCK') ...

Locking

hasLock

Check whether the folder has the lock.

Examples:

if($locker->hasLock) {...}
if($folder->locker->hasLock) {...}
isLocked

Test if the folder is locked by this or a different application.

Examples:

if($locker->isLocked) {...}
if($folder->isLocked) {...}
lock FOLDER

Get a lock on a folder. This will return false if the lock fails.

Examples:

die unless $locker->lock;
if($folder->lock) {...}
unlock

Undo the lock on a folder.

Examples:

$locker->unlock;
$folder->unlock;

Logging and Tracing

defaultTrace [LEVEL, [LEVEL]

See Mail::Reporter::defaultTrace()

errors

See Mail::Reporter::errors()

log [LEVEL [,STRINGS]]

See Mail::Reporter::log()

report [LEVEL]

See Mail::Reporter::report()

reportAll [LEVEL]

See Mail::Reporter::reportAll()

trace [LEVEL]

See Mail::Reporter::trace()

warnings

See Mail::Reporter::warnings()

Other Methods

AUTOLOAD

See Mail::Reporter::AUTOLOAD()

inGlobalDestruction

See Mail::Reporter::inGlobalDestruction()

logPriority LEVEL

See Mail::Reporter::logPriority()

logSettings

See Mail::Reporter::logSettings()

notImplemented

See Mail::Reporter::notImplemented()

SEE ALSO

A good start to read is Mail::Box-Overview. More documentation and a mailinglist are available from the project's website at http://perl.overmeer.net/mailbox/.

AUTHOR

Mark Overmeer (mark@overmeer.net) with the help of many.

VERSION

This code is beta, version 2.022.

Copyright (c) 2001-2002 Mark Overmeer. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.