diff options
| -rw-r--r-- | bot/utils/lock.py | 62 |
1 files changed, 25 insertions, 37 deletions
diff --git a/bot/utils/lock.py b/bot/utils/lock.py index 7aaafbc88..e44776340 100644 --- a/bot/utils/lock.py +++ b/bot/utils/lock.py @@ -1,3 +1,4 @@ +import asyncio import inspect import logging from collections import defaultdict @@ -16,39 +17,21 @@ _IdCallable = Callable[[function.BoundArgs], _IdCallableReturn] ResourceId = Union[Hashable, _IdCallable] -class LockGuard: - """ - A context manager which acquires and releases a lock (mutex). - - Raise RuntimeError if trying to acquire a locked lock. - """ - - def __init__(self): - self._locked = False - - @property - def locked(self) -> bool: - """Return True if currently locked or False if unlocked.""" - return self._locked - - def __enter__(self): - if self._locked: - raise RuntimeError("Cannot acquire a locked lock.") - - self._locked = True - - def __exit__(self, _exc_type, _exc_value, _traceback): # noqa: ANN001 - self._locked = False - return False # Indicate any raised exception shouldn't be suppressed. - - -def lock(namespace: Hashable, resource_id: ResourceId, *, raise_error: bool = False) -> Callable: +def lock( + namespace: Hashable, + resource_id: ResourceId, + *, + raise_error: bool = False, + wait: bool = False, +) -> Callable: """ Turn the decorated coroutine function into a mutually exclusive operation on a `resource_id`. - If any other mutually exclusive function currently holds the lock for a resource, do not run the - decorated function and return None. If `raise_error` is True, raise `LockedResourceError` if - the lock cannot be acquired. + If `wait` is True, wait until the lock becomes available. Otherwise, if any other mutually + exclusive function currently holds the lock for a resource, do not run the decorated function + and return None. + + If `raise_error` is True, raise `LockedResourceError` if the lock cannot be acquired. `namespace` is an identifier used to prevent collisions among resource IDs. @@ -78,15 +61,19 @@ def lock(namespace: Hashable, resource_id: ResourceId, *, raise_error: bool = Fa else: id_ = resource_id - log.trace(f"{name}: getting lock for resource {id_!r} under namespace {namespace!r}") + log.trace(f"{name}: getting the lock object for resource {namespace!r}:{id_!r}") # Get the lock for the ID. Create a lock if one doesn't exist yet. locks = __lock_dicts[namespace] - lock_guard = locks.setdefault(id_, LockGuard()) - - if not lock_guard.locked: - log.debug(f"{name}: resource {namespace!r}:{id_!r} is free; acquiring it...") - with lock_guard: + lock_ = locks.setdefault(id_, asyncio.Lock()) + + # It's safe to check an asyncio.Lock is free before acquiring it because: + # 1. Synchronous code like `if not lock_.locked()` does not yield execution + # 2. `asyncio.Lock.acquire()` does not internally await anything if the lock is free + # 3. awaits only yield execution to the event loop at actual I/O boundaries + if wait or not lock_.locked(): + log.debug(f"{name}: acquiring lock for resource {namespace!r}:{id_!r}...") + async with lock_: return await func(*args, **kwargs) else: log.info(f"{name}: aborted because resource {namespace!r}:{id_!r} is locked") @@ -103,6 +90,7 @@ def lock_arg( func: Callable[[Any], _IdCallableReturn] = None, *, raise_error: bool = False, + wait: bool = False, ) -> Callable: """ Apply the `lock` decorator using the value of the arg at the given name/position as the ID. @@ -110,5 +98,5 @@ def lock_arg( `func` is an optional callable or awaitable which will return the ID given the argument value. See `lock` docs for more information. """ - decorator_func = partial(lock, namespace, raise_error=raise_error) + decorator_func = partial(lock, namespace, raise_error=raise_error, wait=wait) return function.get_arg_value_wrapper(decorator_func, name_or_pos, func) |