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Avoid deadlock problems

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Explicitly use write locks, instead of read locks (that are later
upgraded) unless we know we will never modify the repository
This commit is contained in:
Jonas Borgström 2014-05-31 15:39:51 +02:00
parent af3e78e6b2
commit 64cd6632a1
5 changed files with 30 additions and 20 deletions
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14
attic/archiver.py
View file

@ -27,11 +27,11 @@ class Archiver:
def __init__(self):
self.exit_code = 0
def open_repository(self, location, create=False):
def open_repository(self, location, create=False, exclusive=False):
if location.proto == 'ssh':
repository = RemoteRepository(location, create=create)
else:
repository = Repository(location.path, create=create)
repository = Repository(location.path, create=create, exclusive=exclusive)
repository._location = location
return repository
@ -56,7 +56,7 @@ class Archiver:
def do_init(self, args):
"""Initialize an empty repository"""
print('Initializing repository at "%s"' % args.repository.orig)
repository = self.open_repository(args.repository, create=True)
repository = self.open_repository(args.repository, create=True, exclusive=True)
key = key_creator(repository, args)
manifest = Manifest(key, repository)
manifest.key = key
@ -66,7 +66,7 @@ class Archiver:
def do_check(self, args):
"""Check repository consistency"""
repository = self.open_repository(args.repository)
repository = self.open_repository(args.repository, exclusive=args.repair)
if args.repair:
while not os.environ.get('ATTIC_CHECK_I_KNOW_WHAT_I_AM_DOING'):
self.print_error("""Warning: 'check --repair' is an experimental feature that might result
@ -95,7 +95,7 @@ Type "Yes I am sure" if you understand this and want to continue.\n""")
def do_create(self, args):
"""Create new archive"""
t0 = datetime.now()
repository = self.open_repository(args.archive)
repository = self.open_repository(args.archive, exclusive=True)
manifest, key = Manifest.load(repository)
cache = Cache(repository, key, manifest)
archive = Archive(repository, key, manifest, args.archive.archive, cache=cache,
@ -216,7 +216,7 @@ Type "Yes I am sure" if you understand this and want to continue.\n""")
def do_delete(self, args):
"""Delete an existing archive"""
repository = self.open_repository(args.archive)
repository = self.open_repository(args.archive, exclusive=True)
manifest, key = Manifest.load(repository)
cache = Cache(repository, key, manifest)
archive = Archive(repository, key, manifest, args.archive.archive, cache=cache)
@ -308,7 +308,7 @@ Type "Yes I am sure" if you understand this and want to continue.\n""")
def do_prune(self, args):
"""Prune repository archives according to specified rules"""
repository = self.open_repository(args.repository)
repository = self.open_repository(args.repository, exclusive=True)
manifest, key = Manifest.load(repository)
cache = Cache(repository, key, manifest)
archives = list(sorted(Archive.list_archives(repository, key, manifest, cache),

22
attic/helpers.py
View file

@ -33,7 +33,10 @@ class ExtensionModuleError(Error):
class UpgradableLock:
class LockUpgradeFailed(Error):
class ReadLockFailed(Error):
"""Failed to acquire read lock on {}"""
class WriteLockFailed(Error):
"""Failed to acquire write lock on {}"""
def __init__(self, path, exclusive=False):
@ -42,10 +45,17 @@ class UpgradableLock:
self.fd = open(path, 'r+')
except IOError:
self.fd = open(path, 'r')
if exclusive:
fcntl.lockf(self.fd, fcntl.LOCK_EX)
else:
fcntl.lockf(self.fd, fcntl.LOCK_SH)
try:
if exclusive:
fcntl.lockf(self.fd, fcntl.LOCK_EX)
else:
fcntl.lockf(self.fd, fcntl.LOCK_SH)
# Python 3.2 raises IOError, Python3.3+ raises OSError
except (IOError, OSError):
if exclusive:
raise self.WriteLockFailed(self.path)
else:
raise self.ReadLockFailed(self.path)
self.is_exclusive = exclusive
def upgrade(self):
@ -53,7 +63,7 @@ class UpgradableLock:
fcntl.lockf(self.fd, fcntl.LOCK_EX)
# Python 3.2 raises IOError, Python3.3+ raises OSError
except (IOError, OSError):
raise self.LockUpgradeFailed(self.path)
raise self.WriteLockFailed(self.path)
self.is_exclusive = True
def release(self):

8
attic/repository.py
View file

@ -44,7 +44,7 @@ class Repository(object):
class CheckNeeded(Error):
'''Inconsistency detected. Please run "attic check {}"'''
def __init__(self, path, create=False):
def __init__(self, path, create=False, exclusive=False):
self.path = path
self.io = None
self.lock = None
@ -52,7 +52,7 @@ class Repository(object):
self._active_txn = False
if create:
self.create(path)
self.open(path)
self.open(path, exclusive)
def __del__(self):
self.close()
@ -98,7 +98,7 @@ class Repository(object):
self.replay_segments(replay_from, segments_transaction_id)
return self.get_index_transaction_id()
def open(self, path):
def open(self, path, exclusive):
self.path = path
if not os.path.isdir(path):
raise self.DoesNotExist(path)
@ -106,7 +106,7 @@ class Repository(object):
self.config.read(os.path.join(self.path, 'config'))
if not 'repository' in self.config.sections() or self.config.getint('repository', 'version') != 1:
raise self.InvalidRepository(path)
self.lock = UpgradableLock(os.path.join(path, 'config'))
self.lock = UpgradableLock(os.path.join(path, 'config'), exclusive)
self.max_segment_size = self.config.getint('repository', 'max_segment_size')
self.segments_per_dir = self.config.getint('repository', 'segments_per_dir')
self.id = unhexlify(self.config.get('repository', 'id').strip())

2
attic/testsuite/helpers.py
View file

@ -120,7 +120,7 @@ class UpgradableLockTestCase(AtticTestCase):
file = tempfile.NamedTemporaryFile()
os.chmod(file.name, 0o444)
lock = UpgradableLock(file.name)
self.assert_raises(UpgradableLock.LockUpgradeFailed, lock.upgrade)
self.assert_raises(UpgradableLock.WriteLockFailed, lock.upgrade)
lock.release()

4
attic/testsuite/repository.py
View file

@ -154,9 +154,9 @@ class RepositoryCommitTestCase(RepositoryTestCaseBase):
for name in os.listdir(self.repository.path):
if name.startswith('index.'):
os.unlink(os.path.join(self.repository.path, name))
with patch.object(UpgradableLock, 'upgrade', side_effect=UpgradableLock.LockUpgradeFailed) as upgrade:
with patch.object(UpgradableLock, 'upgrade', side_effect=UpgradableLock.WriteLockFailed) as upgrade:
self.reopen()
self.assert_raises(UpgradableLock.LockUpgradeFailed, lambda: len(self.repository))
self.assert_raises(UpgradableLock.WriteLockFailed, lambda: len(self.repository))
upgrade.assert_called_once()