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113 lines
4.0 KiB
113 lines
4.0 KiB
# Copyright 2017 The Chromium OS Authors. All rights reserved.
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# Use of this source code is governed by a BSD-style license that can be
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# found in the LICENSE file.
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import contextlib
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import errno
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import common
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from autotest_lib.server.hosts import host_info
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from chromite.lib import locking
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from chromite.lib import retry_util
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_FILE_LOCK_TIMEOUT_SECONDS = 5
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class FileStore(host_info.CachingHostInfoStore):
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"""A CachingHostInfoStore backed by an on-disk file."""
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def __init__(self, store_file,
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file_lock_timeout_seconds=_FILE_LOCK_TIMEOUT_SECONDS):
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"""
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@param store_file: Absolute path to the backing file to use.
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@param info: Optional HostInfo to initialize the store. When not None,
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any data in store_file will be overwritten.
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@param file_lock_timeout_seconds: Timeout for aborting the attempt to
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lock the backing file in seconds. Set this to <= 0 to request
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just a single attempt.
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"""
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super(FileStore, self).__init__()
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self._store_file = store_file
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self._lock_path = '%s.lock' % store_file
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if file_lock_timeout_seconds <= 0:
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self._lock_max_retry = 0
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self._lock_sleep = 0
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else:
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# A total of 3 attempts at times (0 + sleep + 2*sleep).
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self._lock_max_retry = 2
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self._lock_sleep = file_lock_timeout_seconds / 3.0
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self._lock = locking.FileLock(
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self._lock_path,
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locktype=locking.FLOCK,
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description='Locking FileStore to read/write HostInfo.',
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blocking=False)
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def __str__(self):
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return '%s[%s]' % (type(self).__name__, self._store_file)
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def _refresh_impl(self):
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"""See parent class docstring."""
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with self._lock_backing_file():
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return self._refresh_impl_locked()
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def _commit_impl(self, info):
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"""See parent class docstring."""
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with self._lock_backing_file():
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return self._commit_impl_locked(info)
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def _refresh_impl_locked(self):
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"""Same as _refresh_impl, but assumes relevant files are locked."""
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try:
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with open(self._store_file, 'r') as fp:
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return host_info.json_deserialize(fp)
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except IOError as e:
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if e.errno == errno.ENOENT:
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raise host_info.StoreError(
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'No backing file. You must commit to the store before '
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'trying to read a value from it.')
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raise host_info.StoreError('Failed to read backing file (%s) : %r'
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% (self._store_file, e))
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except host_info.DeserializationError as e:
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raise host_info.StoreError(
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'Failed to desrialize backing file %s: %r' %
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(self._store_file, e))
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def _commit_impl_locked(self, info):
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"""Same as _commit_impl, but assumes relevant files are locked."""
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try:
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with open(self._store_file, 'w') as fp:
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host_info.json_serialize(info, fp)
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except IOError as e:
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raise host_info.StoreError('Failed to write backing file (%s) : %r'
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% (self._store_file, e))
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@contextlib.contextmanager
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def _lock_backing_file(self):
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"""Context to lock the backing store file.
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@raises StoreError if the backing file can not be locked.
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"""
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def _retry_locking_failures(exc):
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return isinstance(exc, locking.LockNotAcquiredError)
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try:
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retry_util.GenericRetry(
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handler=_retry_locking_failures,
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functor=self._lock.write_lock,
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max_retry=self._lock_max_retry,
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sleep=self._lock_sleep)
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# If self._lock fails to write the locking file, it'll leak an OSError
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except (locking.LockNotAcquiredError, OSError) as e:
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raise host_info.StoreError(e)
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with self._lock:
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yield
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