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# lock.py - simple locking scheme for mercurial
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#
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# Copyright 2005, 2006 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 errno, os, socket, time, util, error
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class lock(object):
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# lock is symlink on platforms that support it, file on others.
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# symlink is used because create of directory entry and contents
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# are atomic even over nfs.
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# old-style lock: symlink to pid
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# new-style lock: symlink to hostname:pid
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_host = None
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def __init__(self, file, timeout=-1, releasefn=None, desc=None):
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self.f = file
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self.held = 0
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self.timeout = timeout
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self.releasefn = releasefn
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self.desc = desc
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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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timeout = self.timeout
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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 error.LockHeld, inst:
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if timeout != 0:
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time.sleep(1)
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if timeout > 0:
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timeout -= 1
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continue
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raise error.LockHeld(errno.ETIMEDOUT, inst.filename, self.desc,
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inst.locker)
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def trylock(self):
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if lock._host is None:
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lock._host = socket.gethostname()
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lockname = '%s:%s' % (lock._host, os.getpid())
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while not self.held:
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try:
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util.makelock(lockname, self.f)
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self.held = 1
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except (OSError, IOError), why:
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if why.errno == errno.EEXIST:
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locker = self.testlock()
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if locker is not None:
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raise error.LockHeld(errno.EAGAIN, self.f, self.desc,
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locker)
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else:
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raise error.LockUnavailable(why.errno, why.strerror,
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why.filename, self.desc)
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def testlock(self):
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"""return id of locker if lock is valid, else None.
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If old-style lock, we cannot tell what machine locker is on.
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with new-style lock, if locker is on this machine, we can
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see if locker is alive. If locker is on this machine but
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not alive, we can safely break lock.
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The lock file is only deleted when None is returned.
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"""
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locker = util.readlock(self.f)
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try:
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host, pid = locker.split(":", 1)
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except ValueError:
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return locker
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if host != lock._host:
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return locker
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try:
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pid = int(pid)
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except:
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return locker
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if util.testpid(pid):
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return locker
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# if locker dead, break lock. must do this with another lock
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# held, or can race and break valid lock.
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try:
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l = lock(self.f + '.break')
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l.trylock()
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os.unlink(self.f)
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l.release()
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except error.LockError:
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return locker
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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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if self.releasefn:
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self.releasefn()
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try:
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os.unlink(self.f)
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except: pass
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