156 lines
4.9 KiB
Python
156 lines
4.9 KiB
Python
##############################################################################
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# Copyright (c) 2013, 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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# Written 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://scalability-llnl.github.io/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 General Public License (as published by
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# the Free Software Foundation) version 2.1 dated 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 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 License
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# along with this program; if not, write to the Free Software Foundation,
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# Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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##############################################################################
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"""Lock implementation for shared filesystems."""
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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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# Default timeout for locks.
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DEFAULT_TIMEOUT = 60
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class _ReadLockContext(object):
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"""Context manager that takes and releases a read lock.
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Arguments are lock and timeout (default 5 minutes)
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"""
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def __init__(self, lock, timeout=DEFAULT_TIMEOUT):
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self._lock = lock
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self._timeout = timeout
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def __enter__(self):
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self._lock.acquire_read(self._timeout)
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def __exit__(self,type,value,traceback):
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self._lock.release_read()
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class _WriteLockContext(object):
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"""Context manager that takes and releases a write lock.
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Arguments are lock and timeout (default 5 minutes)
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"""
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def __init__(self, lock, timeout=DEFAULT_TIMEOUT):
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self._lock = lock
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self._timeout = timeout
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def __enter__(self):
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self._lock.acquire_write(self._timeout)
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def __exit__(self,type,value,traceback):
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self._lock.release_write()
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class Lock(object):
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"""Distributed file-based lock using ``flock``."""
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def __init__(self, file_path):
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self._file_path = file_path
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self._fd = os.open(file_path,os.O_RDWR)
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self._reads = 0
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self._writes = 0
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def write_lock(self, timeout=DEFAULT_TIMEOUT):
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"""Convenience method that returns a write lock context."""
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return _WriteLockContext(self, timeout)
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def read_lock(self, timeout=DEFAULT_TIMEOUT):
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"""Convenience method that returns a read lock context."""
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return _ReadLockContext(self, timeout)
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def acquire_read(self, timeout):
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"""
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Implements recursive lock. If held in both read and write mode,
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the write lock will be maintained until all locks are released
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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)
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self._reads += 1
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def acquire_write(self, timeout):
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"""
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Implements recursive lock
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"""
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if self._writes == 0:
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self._lock(fcntl.LOCK_EX, timeout)
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self._writes += 1
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def _lock(self, op, timeout):
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"""
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The timeout is implemented using nonblocking flock()
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to avoid using signals for timing
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Write locks store pid and host information to the lock file
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Read locks do not store data
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"""
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total_time = 0
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while total_time < timeout:
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try:
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fcntl.flock(self._fd, op | fcntl.LOCK_NB)
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if op == fcntl.LOCK_EX:
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with open(self._file_path, 'w') as f:
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f.write("pid = " + str(os.getpid()) + ", host = " + 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 == EACCES:
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pass
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else:
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raise
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time.sleep(0.1)
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total_time += 0.1
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def release_read(self):
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"""
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Assert there is a lock of the right type to release, recursive lock
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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()
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self._reads -= 1
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def release_write(self):
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"""
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Assert there is a lock of the right type to release, recursive lock
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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()
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self._writes -= 1
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def _unlock(self):
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"""
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Releases the lock regardless of mode. Note that read locks may be
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masquerading as write locks at times, but this removes either.
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"""
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fcntl.flock(self._fd, fcntl.LOCK_UN)
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