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Viewing changes to vendor/lockfile/lockfile/linklockfile.py

  • Committer: Jesse Andrews
  • Date: 2010-05-28 06:05:26 UTC
  • Revision ID: git-v1:bf6e6e718cdc7488e2da87b21e258ccc065fe499
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vendor/lockfile/lockfile/linklockfile.py
 
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from __future__ import absolute_import
 
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import time
 
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import os
 
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from . import (LockBase, LockFailed, NotLocked, NotMyLock, LockTimeout,
 
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               AlreadyLocked)
 
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class LinkLockFile(LockBase):
 
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    """Lock access to a file using atomic property of link(2).
 
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    >>> lock = LinkLockFile('somefile')
 
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    >>> lock = LinkLockFile('somefile', threaded=False)
 
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    """
 
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    def acquire(self, timeout=None):
 
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        try:
 
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            open(self.unique_name, "wb").close()
 
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        except IOError:
 
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            raise LockFailed("failed to create %s" % self.unique_name)
 
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        end_time = time.time()
 
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        if timeout is not None and timeout > 0:
 
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            end_time += timeout
 
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        while True:
 
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            # Try and create a hard link to it.
 
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            try:
 
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                print 'making a hard link %s to %s' % (self.unique_name,
 
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                                                       self.lock_file)
 
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                os.link(self.unique_name, self.lock_file)
 
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            except OSError:
 
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                # Link creation failed.  Maybe we've double-locked?
 
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                nlinks = os.stat(self.unique_name).st_nlink
 
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                if nlinks == 2:
 
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                    # The original link plus the one I created == 2.  We're
 
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                    # good to go.
 
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                    return
 
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                else:
 
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                    # Otherwise the lock creation failed.
 
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                    if timeout is not None and time.time() > end_time:
 
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                        os.unlink(self.unique_name)
 
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                        if timeout > 0:
 
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                            raise LockTimeout
 
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                        else:
 
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                            raise AlreadyLocked
 
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                    time.sleep(timeout is not None and timeout/10 or 0.1)
 
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            else:
 
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                # Link creation succeeded.  We're good to go.
 
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                return
 
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    def release(self):
 
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        if not self.is_locked():
 
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            raise NotLocked
 
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        elif not os.path.exists(self.unique_name):
 
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            raise NotMyLock
 
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        os.unlink(self.unique_name)
 
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        os.unlink(self.lock_file)
 
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    def is_locked(self):
 
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        return os.path.exists(self.lock_file)
 
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    def i_am_locking(self):
 
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        return (self.is_locked() and
 
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                os.path.exists(self.unique_name) and
 
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                os.stat(self.unique_name).st_nlink == 2)
 
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    def break_lock(self):
 
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        if os.path.exists(self.lock_file):
 
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            os.unlink(self.lock_file)
 
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