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Viewing changes to Imaginary/pottery/persistence.py

  • Committer: exarkun
  • Date: 2006-02-26 02:37:39 UTC
  • Revision ID: svn-v4:866e43f7-fbfc-0310-8f2a-ec88d1da2979:trunk:4991
Merge move-pottery-to-trunk

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Imaginary/pottery/persistence.py
 
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"""Persistence support for Pottery
 
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For now, this defines a service which holds a reference to the game's
 
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realm instance.  Periodically, the realm is pickled and written to
 
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disk.  When the service is created, if an existing pickled realm
 
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exists on disk, it is loaded and used instead of the realm passed in.
 
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"""
 
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import os, errno
 
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import cPickle as pickle
 
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from twisted.application import service
 
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from twisted.internet import task
 
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from twisted.python import log
 
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class PersistenceService(service.Service):
 
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    def __init__(self, fname, realm):
 
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        self.fname = fname
 
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        if os.path.exists(fname):
 
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            realm = self._unpersist()
 
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        self.realm = realm
 
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    def startService(self):
 
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        self.loop = task.LoopingCall(self._persist)
 
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        self.loop.start(60).addErrback(log.err)
 
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    def stopService(self):
 
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        self.loop.stop()
 
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        self._persist()
 
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    def _persist(self):
 
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        # Try to reap the previous persistence child.
 
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        try:
 
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            os.waitpid(-1, os.WNOHANG)
 
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        except OSError, e:
 
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            if e.errno != errno.ECHILD:
 
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                raise
 
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        # Fork and continue normal execution in the parent.  In the child,
 
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        # try to acquire the persist lock.  If it cannot be acquired,
 
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        # return.  Otherwise, pickle game state to a new file, move the
 
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        # entire result over the existing game state file, and release the
 
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        # lock.
 
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        pid = os.fork()
 
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        if pid == 0:
 
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            try:
 
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                try:
 
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                    os.mkdir(self.fname + '.lock')
 
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                except OSError, e:
 
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                    if e.errno != errno.EEXIST:
 
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                        raise
 
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                else:
 
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                    try:
 
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                        fObj = file(self.fname + '.tmp', 'wb')
 
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                        fObj.write(pickle.dumps(self.realm))
 
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                        fObj.close()
 
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                        os.rename(self.fname + '.tmp', self.fname)
 
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                    finally:
 
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                        os.rmdir(self.fname + '.lock')
 
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            finally:
 
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                os._exit(0)
 
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    def _unpersist(self):
 
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        fObj = file(self.fname, 'rb')
 
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        return pickle.loads(fObj.read())
 
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