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Full Discussion: Atomic lock file creation
Top Forums Programming Atomic lock file creation Post 302274515 by Perderabo on Wednesday 7th of January 2009 07:31:36 PM
Old 01-07-2009
There are lots of file operation system calls with absolute guarantees of atomicity. The link system call is the one most often used in locking techniques. First create a temporary file in a well known directory. Then attempt to link() it to a well known name. If two processes try this at the same time, one will succeed and the other fail. If the link works, you own the lock.

For file updates, you can link the file to a lock file. Programs that update /etc/passwd and /etc/shadow often use this technique. They try to link /etc/passwd to /etc/opasswd and /etc/shadow to /etc/oshadow. Using truss and strace, I see that redhat linux and Solaris 8 are still doing that. This was the original way to lock files between cooperating processes.
 

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DateTime::TimeZone::Local::Win32(3)			User Contributed Perl Documentation		       DateTime::TimeZone::Local::Win32(3)

NAME
DateTime::TimeZone::Local::Win32 - Determine the local system's time zone on Windows VERSION
version 1.63 SYNOPSIS
my $tz = DateTime::TimeZone->new( name => 'local' ); my $tz = DateTime::TimeZone::Local->TimeZone(); DESCRIPTION
This module provides methods for determining the local time zone on a Windows platform. HOW THE TIME ZONE IS DETERMINED
This class tries the following methods of determining the local time zone: o $ENV{TZ} It checks $ENV{TZ} for a valid time zone name. o Windows Registry When using the registry, we look for the Windows time zone and use a mapping to translate this to an Olson time zone name. o Windows Vista and 2008 We look in "SYSTEM/CurrentControlSet/Control/TimeZoneInformation/" for a node named "/TimeZoneKeyName". If this exists, we use this key to look up the Olson time zone name in our mapping. o Windows NT, Windows 2000, Windows XP, Windows 2003 Server We look in "SOFTWARE/Microsoft/Windows NT/CurrentVersion/Time Zones/" and loop through all of its sub keys. For each sub key, we compare the value of the key with "/Std" appended to the end to the value of "SYSTEM/CurrentControlSet/Control/TimeZoneInformation/StandardName". This gives us the English name of the Windows time zone, which we use to look up the Olson time zone name. o Windows 95, Windows 98, Windows Millenium Edition The algorithm is the same as for NT, but we loop through the sub keys of "SOFTWARE/Microsoft/Windows/CurrentVersion/Time Zones/" AUTHOR
Dave Rolsky <autarch@urth.org> COPYRIGHT AND LICENSE
This software is copyright (c) 2013 by Dave Rolsky. This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself. perl v5.18.2 2013-10-28 DateTime::TimeZone::Local::Win32(3)
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