4710c53dca
These files are a subset of the python-2.7.2.tgz distribution from python.org. Changed files from PyMod-2.7.2 have been copied into the corresponding directories of this tree, replacing the original files in the distribution. Signed-off-by: daryl.mcdaniel@intel.com git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13197 6f19259b-4bc3-4df7-8a09-765794883524
281 lines
6.9 KiB
Python
281 lines
6.9 KiB
Python
"""CVS locking algorithm.
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CVS locking strategy
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====================
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As reverse engineered from the CVS 1.3 sources (file lock.c):
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- Locking is done on a per repository basis (but a process can hold
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write locks for multiple directories); all lock files are placed in
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the repository and have names beginning with "#cvs.".
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- Before even attempting to lock, a file "#cvs.tfl.<pid>" is created
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(and removed again), to test that we can write the repository. [The
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algorithm can still be fooled (1) if the repository's mode is changed
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while attempting to lock; (2) if this file exists and is writable but
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the directory is not.]
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- While creating the actual read/write lock files (which may exist for
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a long time), a "meta-lock" is held. The meta-lock is a directory
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named "#cvs.lock" in the repository. The meta-lock is also held while
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a write lock is held.
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- To set a read lock:
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- acquire the meta-lock
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- create the file "#cvs.rfl.<pid>"
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- release the meta-lock
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- To set a write lock:
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- acquire the meta-lock
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- check that there are no files called "#cvs.rfl.*"
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- if there are, release the meta-lock, sleep, try again
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- create the file "#cvs.wfl.<pid>"
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- To release a write lock:
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- remove the file "#cvs.wfl.<pid>"
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- rmdir the meta-lock
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- To release a read lock:
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- remove the file "#cvs.rfl.<pid>"
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Additional notes
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----------------
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- A process should read-lock at most one repository at a time.
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- A process may write-lock as many repositories as it wishes (to avoid
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deadlocks, I presume it should always lock them top-down in the
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directory hierarchy).
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- A process should make sure it removes all its lock files and
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directories when it crashes.
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- Limitation: one user id should not be committing files into the same
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repository at the same time.
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Turn this into Python code
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--------------------------
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rl = ReadLock(repository, waittime)
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wl = WriteLock(repository, waittime)
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list = MultipleWriteLock([repository1, repository2, ...], waittime)
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"""
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import os
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import time
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import stat
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import pwd
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# Default wait time
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DELAY = 10
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# XXX This should be the same on all Unix versions
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EEXIST = 17
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# Files used for locking (must match cvs.h in the CVS sources)
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CVSLCK = "#cvs.lck"
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CVSRFL = "#cvs.rfl."
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CVSWFL = "#cvs.wfl."
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class Error:
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def __init__(self, msg):
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self.msg = msg
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def __repr__(self):
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return repr(self.msg)
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def __str__(self):
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return str(self.msg)
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class Locked(Error):
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pass
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class Lock:
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def __init__(self, repository = ".", delay = DELAY):
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self.repository = repository
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self.delay = delay
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self.lockdir = None
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self.lockfile = None
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pid = repr(os.getpid())
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self.cvslck = self.join(CVSLCK)
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self.cvsrfl = self.join(CVSRFL + pid)
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self.cvswfl = self.join(CVSWFL + pid)
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def __del__(self):
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print "__del__"
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self.unlock()
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def setlockdir(self):
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while 1:
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try:
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self.lockdir = self.cvslck
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os.mkdir(self.cvslck, 0777)
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return
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except os.error, msg:
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self.lockdir = None
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if msg[0] == EEXIST:
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try:
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st = os.stat(self.cvslck)
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except os.error:
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continue
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self.sleep(st)
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continue
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raise Error("failed to lock %s: %s" % (
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self.repository, msg))
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def unlock(self):
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self.unlockfile()
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self.unlockdir()
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def unlockfile(self):
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if self.lockfile:
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print "unlink", self.lockfile
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try:
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os.unlink(self.lockfile)
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except os.error:
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pass
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self.lockfile = None
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def unlockdir(self):
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if self.lockdir:
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print "rmdir", self.lockdir
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try:
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os.rmdir(self.lockdir)
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except os.error:
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pass
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self.lockdir = None
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def sleep(self, st):
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sleep(st, self.repository, self.delay)
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def join(self, name):
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return os.path.join(self.repository, name)
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def sleep(st, repository, delay):
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if delay <= 0:
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raise Locked(st)
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uid = st[stat.ST_UID]
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try:
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pwent = pwd.getpwuid(uid)
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user = pwent[0]
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except KeyError:
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user = "uid %d" % uid
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print "[%s]" % time.ctime(time.time())[11:19],
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print "Waiting for %s's lock in" % user, repository
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time.sleep(delay)
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class ReadLock(Lock):
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def __init__(self, repository, delay = DELAY):
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Lock.__init__(self, repository, delay)
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ok = 0
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try:
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self.setlockdir()
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self.lockfile = self.cvsrfl
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fp = open(self.lockfile, 'w')
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fp.close()
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ok = 1
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finally:
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if not ok:
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self.unlockfile()
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self.unlockdir()
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class WriteLock(Lock):
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def __init__(self, repository, delay = DELAY):
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Lock.__init__(self, repository, delay)
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self.setlockdir()
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while 1:
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uid = self.readers_exist()
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if not uid:
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break
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self.unlockdir()
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self.sleep(uid)
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self.lockfile = self.cvswfl
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fp = open(self.lockfile, 'w')
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fp.close()
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def readers_exist(self):
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n = len(CVSRFL)
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for name in os.listdir(self.repository):
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if name[:n] == CVSRFL:
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try:
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st = os.stat(self.join(name))
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except os.error:
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continue
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return st
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return None
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def MultipleWriteLock(repositories, delay = DELAY):
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while 1:
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locks = []
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for r in repositories:
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try:
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locks.append(WriteLock(r, 0))
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except Locked, instance:
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del locks
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break
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else:
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break
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sleep(instance.msg, r, delay)
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return list
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def test():
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import sys
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if sys.argv[1:]:
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repository = sys.argv[1]
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else:
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repository = "."
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rl = None
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wl = None
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try:
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print "attempting write lock ..."
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wl = WriteLock(repository)
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print "got it."
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wl.unlock()
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print "attempting read lock ..."
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rl = ReadLock(repository)
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print "got it."
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rl.unlock()
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finally:
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print [1]
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sys.exc_traceback = None
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print [2]
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if rl:
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rl.unlock()
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print [3]
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if wl:
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wl.unlock()
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print [4]
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rl = None
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print [5]
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wl = None
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print [6]
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if __name__ == '__main__':
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test()
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