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landscape/lib/lock.py

 

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import fcntl

 

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import time

 

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import os

 

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class LockError(Exception):

 

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    """Raised when unable to lock a file."""

 

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def lock_path(path, timeout=0):

 

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    fd = os.open(path, os.O_CREAT)

 

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    flags = fcntl.fcntl(fd, fcntl.F_GETFD, 0)

 

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    flags |= fcntl.FD_CLOEXEC

 

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    fcntl.fcntl(fd, fcntl.F_SETFD, flags)

 

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    started = time.time()

 

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    while True:

 

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        try:

 

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            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)

 

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        except IOError, e:

 

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            if started < time.time() - timeout:

 

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                raise LockError("Couldn't obtain lock")

 

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        else:

 

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            break

 

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        time.sleep(0.1)

 

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    def unlock_path():

 

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        fcntl.flock(fd, fcntl.LOCK_UN)

 

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        os.close(fd)

 

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    return unlock_path

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