#! python:
#w#VIC vic_mutex.py module
#
# Copyright 2002, 2003 by Timothy Rue <3seas@threeseas.net>
#
# VIC vic_mutex.py module: version 0.5.1.python (BETA)
#
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation version 2
# of the License. http://www.gnu.org/copyleft/gpl.html
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
# Or access http://www.gnu.org/copyleft/gpl.html
##########################################################################
#August 29, 2003 made file IQ parseable 0.5.1
#July 24, 2003 initial release 0.5
#
##########################################################################
#! /usr/bin/python
###
### Cross platform Mutex class.
###
### Implements an OS level mutually-exclusive lock on systems that
### support it, and a dodgey probably-work version if not.
###
### Functions:
###    VicMutex.lock()      -- to to acheive mutex
###    VicMutex.release()   -- if mutex is acheived, deactivate the lock
###    VicMutex.isLocked()  -- what is the current status
###

#s#system modules
import time
import os
import os.path

#w#class VicMutex
class VicMutex:
    "VIC Mutex:"

#s#def __init__
    def __init__(self):
        self.fake_mutexes = 0
        try:
            import mutex
            self.the_mutex = mutex.mutex()
            self.time_delay = 0.05
        except:
            self.fake_mutexes = 1
            self.the_mutex_dirname = (os.path).abspath(os.tmpnam())
            self.have_lock = 0
            self.time_delay = 0.5

#s#def __del__
    def __del__(self):
        if (self.fake_mutexes == 1):
            try:
                os.rmdir(self.the_mutex_dirname)
            except:
                pass

#s#def lock
    def lock(self):
        if (self.fake_mutexes):
            ### The mutex principle here is that only one process can successsfully
            ### make a single directory at once.  So if two processes try to both
            ### create the same directory at one, only one will succeed.
            ### Use the act of successful directory creation as the deceiding factor.
            while (1):
                if (os.path.isdir(self.the_mutex_dirname)):
                    self.wait()  # someone else has the mutex
                else:
                    try:
                        ### if <this process> succeeds in making the dir, then we have lock
                        os.mkdir(self.the_mutex_dirname) ### os.mkdir will except if the dir already exists
                        self.have_lock = 1
                        break;
                    except:
                        pass
        else:
            while (not self.the_mutex.testandset()):
                self.wait()

#s#def release
    def release(self):
        if (self.fake_mutexes):
            if (self.have_lock):
                self.have_lock = 0
                os.rmdir(self.the_mutex_dirname)
        else:
            self.the_mutex.unlock()

#s#def isLocked
    def isLocked(self):
        if (self.fake_mutexes):
            return (self.have_lock == 1)
        else:
            return self.the_mutex.test()

#s#def wait
    ### Do not call this function
    def wait(self):
        #print "mutex sleeping..."
        time.sleep(self.time_delay)