Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
Path lock using a read/write/ancestor lock on each ancestor path
import asyncio
import contextlib
import weakref
from fifolock import FifoLock
class ReadAncestor(asyncio.Future):
@staticmethod
def is_compatible(holds):
return not holds[Write]
class Read(asyncio.Future):
@staticmethod
def is_compatible(holds):
return not holds[WriteAncestor] and not holds[Write]
class WriteAncestor(asyncio.Future):
@staticmethod
def is_compatible(holds):
return not holds[Read] and not holds[Write]
class Write(asyncio.Future):
@staticmethod
def is_compatible(holds):
return (
not holds[ReadAncestor] and not holds[Read] and \
not holds[WriteAncestor] and not holds[Write]
)
class PathLock():
def __init__(self):
self._locks = weakref.WeakValueDictionary()
@staticmethod
def _sort_key(path_lock):
return len(path_lock[0].parents), path_lock[0].as_posix()
@staticmethod
def _flatten(to_flatten):
return [
item for sub_list in to_flatten for item in sub_list
]
def _with_locks(self, paths, mode):
return [
(path, self._locks.setdefault(path, default=FifoLock()), mode)
for path in paths
]
@contextlib.asynccontextmanager
async def __call__(self, read, write):
write_paths = set(write)
write_locks = self._with_locks(write_paths, Write)
write_ancestor_paths = set(self._flatten(path.parents for path in write_paths)) \
- write_paths
write_ancestor_locks = self._with_locks(write_ancestor_paths, WriteAncestor)
read_paths = set(read) \
- write_paths - write_ancestor_paths
read_locks = self._with_locks(read_paths, Read)
read_ancestor_paths = set(self._flatten(path.parents for path in read_paths)) \
- write_paths - write_ancestor_paths - read_paths
read_ancestor_locks = self._with_locks(read_ancestor_paths, ReadAncestor)
sorted_locks = sorted(
read_locks + read_ancestor_locks + write_locks + write_ancestor_locks,
key=self._sort_key)
async with contextlib.AsyncExitStack() as stack:
for _, lock, mode in sorted_locks:
await stack.enter_async_context(lock(mode))
yield
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.