Stuart Gathman
4c72135b0e
Test case for delayed DSN parsing. Fix plock when source missing or cannot set owner/group.
67 lines
1.7 KiB
Python
67 lines
1.7 KiB
Python
# Author: Stuart D. Gathman <stuart@bmsi.com>
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# Copyright 2001 Business Management Systems, Inc.
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# This code is under the GNU General Public License. See COPYING for details.
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import os
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from time import sleep
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class PLock(object):
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"A simple /etc/passwd style lock,update,rename protocol for updating files."
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def __init__(self,basename):
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self.basename = basename
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self.fp = None
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def lock(self,lockname=None,mode=0660,strict_perms=False):
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"Start an update transaction. Return FILE to write new version."
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self.unlock()
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if not lockname:
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lockname = self.basename + '.lock'
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self.lockname = lockname
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try:
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st = os.stat(self.basename)
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mode |= st.st_mode
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except OSError: pass
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u = os.umask(0002)
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try:
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fd = os.open(lockname,os.O_WRONLY+os.O_CREAT+os.O_EXCL,mode)
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finally:
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os.umask(u)
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self.fp = os.fdopen(fd,'w')
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try:
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os.chown(self.lockname,-1,st.st_gid)
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except:
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if strict_perms:
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self.unlock()
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raise
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return self.fp
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def wlock(self,lockname=None):
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"Wait until lock is free, then start an update transaction."
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while True:
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try:
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return self.lock(lockname)
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except OSError:
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sleep(2)
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def commit(self,backname=None):
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"Commit update transaction with optional backup file."
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if not self.fp:
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raise IOError,"File not locked"
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self.fp.close()
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self.fp = None
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if backname:
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try:
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os.remove(backname)
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except OSError: pass
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os.link(self.basename,backname)
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os.rename(self.lockname,self.basename)
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def unlock(self):
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"Cancel update transaction."
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if self.fp:
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try:
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self.fp.close()
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except: pass
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self.fp = None
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os.remove(self.lockname)
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