mercurial/lock.py
author mpm@selenic.com
Tue, 07 Jun 2005 08:53:05 -0800
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child 429 688d03d6997a
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# lock.py - simple locking scheme for mercurial
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#
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# Copyright 2005 Matt Mackall <mpm@selenic.com>
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#
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# This software may be used and distributed according to the terms
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# of the GNU General Public License, incorporated herein by reference.
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import os, time
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class LockHeld(Exception):
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    pass
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class lock:
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    def __init__(self, file, wait = 1):
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        self.f = file
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        self.held = 0
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        self.wait = wait
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        self.lock()
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    def __del__(self):
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        self.release()
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    def lock(self):
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        while 1:
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            try:
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                self.trylock()
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                return 1
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            except LockHeld, inst:
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                if self.wait:
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                    time.sleep(1)
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                    continue
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                raise inst
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    def trylock(self):
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        pid = os.getpid()
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        try:
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            os.symlink(str(pid), self.f)
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            self.held = 1
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        except:
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            raise LockHeld(os.readlink(self.f))
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    def release(self):
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        if self.held:
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            self.held = 0
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            os.unlink(self.f)
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