NAME
        Lock::Server - Light-weight socket based resource locking manager.

DESCRIPTION
        This creates a child process socket server that takes lock and 
        unlock requests. The lock requests only return once a lock is
        obtained or a timeout has occurred. A lock may only be locked
        for a specific amount of time before the lock is timed out.

        The protocol used is RESTFUL HTTP though the helper class wraps
        that. It uses the GET verb with the following paths :

         * CHECK/key - returns 1 if the key in question is currently locked 
                       returns 0 if not

         * LOCK/key/requester - returns lock expire time or 0 
                                if there was an error

         * UNLOCK/key/requester - returns 1 if the unlock went as expected, 
                                  0 otherwise

         * VERIFY/key/requester - returns 1 if the key is locked to the
                                  requester and did not time out and 0 
                                  otherwise.
         * PING - returns 1 if the server is active

        This does not do deadlock detection, relying on the timeouts to 
        prevent the system from getting in a hopelessly tangled state.
        Care should be taken, as with any resource locking system, with
        the use of Lock::Server. Adjust the timeouts for what makes sense
        with the system you are designing. The lock requests return with the
        time that the lock will expire.

SYNPOSIS
        use Lock::Server;
        use Lock::Server::Client;

        my $lockServer = new Lock::Server( {
           lock_timeout         => 10, #seconds. default is 3
           lock_attempt_timeout => 12, #seconds. default is 4
           port                 => 888, #default is 8004
           host                 => 'localhost', #default 127.0.0.1
        } );

        if( my $childPid = $lockServer->start ) {
            print "Lock server started in child thread $childPid\n";
        }

        my $lockClient_A = $lockServer->client( "CLIENT_A" );
        my $lockClient_B = 
            new Lock::Server::Client( "CLIENT_B", 'localhost', 888 );

        if( $lockClient_A->lock( "KEYA" ) ) {
           print "Lock Successfull for locker A and KEYA\n";
        } else {
           print "Could not obtain lock in 12 seconds.\n";
        }

        # KEYA for LockerI times out after 10 seconds.
        # Lock Client B waits until it can obtain the lock
        if( $lockClient_B->lock( "KEYA" ) ) {
           print "Lock Successfull for Client B lock 'KEYA'\n";
        } else {
           print "Could not obtain lock in 12 seconds.\n";
        }

        # KEYA for LockerII is now freed. The next locker
        # attempting to lock KEYA will then obtain the lock.
        if( $lockClientB->unlock( "KEYA" ) ) {
           print "Unlock Successfull\n";
        }

        if( $lockServer->stop ) {
            print "Lock server shut down.\n";
        }

METHODS
  Lock::Server::new( $args )
     Creates a new lock server for the given optional arguments.
 
     Arguments are :
       * port - port to serve on. Defaults to 8004
       * lock_timeout - low long should a lock last in seconds
       * lock_attempt_timeout - how long should a requester
                                wait for a lock in seconds

  client( lockername )
        Returns a client with the given name that can send lock and unlock requests for keys.

  stop
        Kills the lock server, breaking off any connections that are waiting for a lock.

  start
        Starts the lock server in a child process, opening up a 
        tcpip socket and returning the child pid or 0 if there
        was an error.

  run
        Runs the lock server.

Helper package
  NAME
        Lock::Server::Client - client for locking server.

  DESCRIPTION
        Sends request to a Lock::Server to lock, unlock and check locks.

  METHODS
   new( lockername, host, port )
        Creates a client object with the given name for the host and port.

   isLocked( key )
        Returns true if the key is locked by anyone.

   lockedByMe( key )
        Returns true if the key is locked by this client or 
        anyone with the name of this client. The name was given in the constructor.

   lock( key )
        Attempt to get the lock for the given key. Returns true if the lock
        was obtained.

   unlock( key )
        Attempt to get unlock the given key. Returns true if the
        key was locked to this client ( or someting with the same name ).

AUTHOR
           Eric Wolf        coyocanid@gmail.com

COPYRIGHT AND LICENSE
           Copyright (c) 2015 Eric Wolf. All rights reserved.  This program is free software; you can redistribute it and/or modify it
           under the same terms as Perl itself.

