249 lines
8.1 KiB
Python
249 lines
8.1 KiB
Python
##############################################################################
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# Copyright (c) 2013-2016, Lawrence Livermore National Security, LLC.
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# Produced at the Lawrence Livermore National Laboratory.
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#
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# This file is part of Spack.
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# Created by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
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# LLNL-CODE-647188
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#
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# For details, see https://github.com/llnl/spack
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# Please also see the LICENSE file for our notice and the LGPL.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU Lesser General Public License (as
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# published by the Free Software Foundation) version 2.1, February 1999.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
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# conditions of the GNU Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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##############################################################################
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import os
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import fcntl
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import errno
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import time
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import socket
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__all__ = ['Lock', 'LockTransaction', 'WriteTransaction', 'ReadTransaction',
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'LockError']
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# Default timeout in seconds, after which locks will raise exceptions.
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_default_timeout = 60
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# Sleep time per iteration in spin loop (in seconds)
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_sleep_time = 1e-5
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class Lock(object):
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"""This is an implementation of a filesystem lock using Python's lockf.
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In Python, `lockf` actually calls `fcntl`, so this should work with any
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filesystem implementation that supports locking through the fcntl calls.
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This includes distributed filesystems like Lustre (when flock is enabled)
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and recent NFS versions.
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"""
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def __init__(self, file_path):
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self._file_path = file_path
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self._fd = None
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self._reads = 0
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self._writes = 0
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def _lock(self, op, timeout):
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"""This takes a lock using POSIX locks (``fnctl.lockf``).
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The lock is implemented as a spin lock using a nonblocking
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call to lockf().
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On acquiring an exclusive lock, the lock writes this process's
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pid and host to the lock file, in case the holding process
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needs to be killed later.
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If the lock times out, it raises a ``LockError``.
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"""
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start_time = time.time()
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while (time.time() - start_time) < timeout:
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try:
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if self._fd is None:
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mode = os.O_RDWR if op == fcntl.LOCK_EX else os.O_RDONLY
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self._fd = os.open(self._file_path, mode)
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fcntl.lockf(self._fd, op | fcntl.LOCK_NB)
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if op == fcntl.LOCK_EX:
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os.write(
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self._fd,
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"pid=%s,host=%s" % (os.getpid(), socket.getfqdn()))
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return
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except IOError as error:
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if error.errno == errno.EAGAIN or error.errno == errno.EACCES:
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pass
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else:
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raise
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time.sleep(_sleep_time)
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raise LockError("Timed out waiting for lock.")
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def _unlock(self):
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"""Releases a lock using POSIX locks (``fcntl.lockf``)
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Releases the lock regardless of mode. Note that read locks may
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be masquerading as write locks, but this removes either.
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"""
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fcntl.lockf(self._fd, fcntl.LOCK_UN)
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os.close(self._fd)
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self._fd = None
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def acquire_read(self, timeout=_default_timeout):
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"""Acquires a recursive, shared lock for reading.
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Read and write locks can be acquired and released in arbitrary
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order, but the POSIX lock is held until all local read and
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write locks are released.
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Returns True if it is the first acquire and actually acquires
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the POSIX lock, False if it is a nested transaction.
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"""
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if self._reads == 0 and self._writes == 0:
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self._lock(fcntl.LOCK_SH, timeout) # can raise LockError.
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self._reads += 1
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return True
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else:
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self._reads += 1
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return False
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def acquire_write(self, timeout=_default_timeout):
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"""Acquires a recursive, exclusive lock for writing.
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Read and write locks can be acquired and released in arbitrary
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order, but the POSIX lock is held until all local read and
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write locks are released.
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Returns True if it is the first acquire and actually acquires
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the POSIX lock, False if it is a nested transaction.
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"""
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if self._writes == 0:
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self._lock(fcntl.LOCK_EX, timeout) # can raise LockError.
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self._writes += 1
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return True
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else:
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self._writes += 1
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return False
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def release_read(self):
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"""Releases a read lock.
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Returns True if the last recursive lock was released, False if
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there are still outstanding locks.
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Does limited correctness checking: if a read lock is released
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when none are held, this will raise an assertion error.
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"""
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assert self._reads > 0
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if self._reads == 1 and self._writes == 0:
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self._unlock() # can raise LockError.
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self._reads -= 1
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return True
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else:
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self._reads -= 1
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return False
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def release_write(self):
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"""Releases a write lock.
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Returns True if the last recursive lock was released, False if
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there are still outstanding locks.
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Does limited correctness checking: if a read lock is released
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when none are held, this will raise an assertion error.
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"""
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assert self._writes > 0
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if self._writes == 1 and self._reads == 0:
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self._unlock() # can raise LockError.
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self._writes -= 1
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return True
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else:
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self._writes -= 1
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return False
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class LockTransaction(object):
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"""Simple nested transaction context manager that uses a file lock.
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This class can trigger actions when the lock is acquired for the
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first time and released for the last.
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If the acquire_fn returns a value, it is used as the return value for
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__enter__, allowing it to be passed as the `as` argument of a `with`
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statement.
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If acquire_fn returns a context manager, *its* `__enter__` function will be
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called in `__enter__` after acquire_fn, and its `__exit__` funciton will be
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called before `release_fn` in `__exit__`, allowing you to nest a context
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manager to be used along with the lock.
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Timeout for lock is customizable.
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"""
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def __init__(self, lock, acquire_fn=None, release_fn=None,
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timeout=_default_timeout):
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self._lock = lock
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self._timeout = timeout
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self._acquire_fn = acquire_fn
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self._release_fn = release_fn
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self._as = None
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def __enter__(self):
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if self._enter() and self._acquire_fn:
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self._as = self._acquire_fn()
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if hasattr(self._as, '__enter__'):
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return self._as.__enter__()
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else:
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return self._as
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def __exit__(self, type, value, traceback):
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suppress = False
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if self._exit():
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if self._as and hasattr(self._as, '__exit__'):
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if self._as.__exit__(type, value, traceback):
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suppress = True
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if self._release_fn:
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if self._release_fn(type, value, traceback):
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suppress = True
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return suppress
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class ReadTransaction(LockTransaction):
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def _enter(self):
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return self._lock.acquire_read(self._timeout)
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def _exit(self):
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return self._lock.release_read()
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class WriteTransaction(LockTransaction):
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def _enter(self):
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return self._lock.acquire_write(self._timeout)
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def _exit(self):
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return self._lock.release_write()
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class LockError(Exception):
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"""Raised when an attempt to acquire a lock times out."""
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