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Make `maybe_open_context()` re-entrant safe, use per factory locks

debug_event_guard
Tyler Goodlet 2022-08-24 12:03:13 -04:00
parent 5ad540c417
commit bafd10a260
1 changed files with 18 additions and 11 deletions
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29
tractor/trionics/_mngrs.py
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@ -81,7 +81,7 @@ async def gather_contexts(
This function is somewhat similar to common usage of This function is somewhat similar to common usage of
``contextlib.AsyncExitStack.enter_async_context()`` (in a loop) in ``contextlib.AsyncExitStack.enter_async_context()`` (in a loop) in
combo with ``asyncio.gather()`` except the managers are concurrently combo with ``asyncio.gather()`` except the managers are concurrently
entered and exited cancellation just works. entered and exited, and cancellation just works.
''' '''
unwrapped: dict[int, Optional[T]] = {}.fromkeys(id(mngr) for mngr in mngrs) unwrapped: dict[int, Optional[T]] = {}.fromkeys(id(mngr) for mngr in mngrs)
@ -119,7 +119,7 @@ class _Cache:
a kept-alive-while-in-use async resource. a kept-alive-while-in-use async resource.
''' '''
lock = trio.Lock() locks: dict[Hashable, trio.Lock] = {}
users: int = 0 users: int = 0
values: dict[Any, Any] = {} values: dict[Any, Any] = {}
resources: dict[ resources: dict[
@ -165,13 +165,18 @@ async def maybe_open_context(
_Cached instance on a _Cache hit. _Cached instance on a _Cache hit.
''' '''
# lock resource acquisition around task racing / ``trio``'s fid = id(acm_func)
# scheduler protocol ctx_key = (fid, key or tuple(kwargs.items()))
await _Cache.lock.acquire()
ctx_key = (id(acm_func), key or tuple(kwargs.items()))
value = None value = None
# Lock resource acquisition around task racing / ``trio``'s
# scheduler protocol.
# NOTE: the lock is target context manager func specific in order
# to allow re-entrant use cases where one `maybe_open_context()`
# wrapped factor may want to call into another.
lock = _Cache.locks.setdefault(fid, trio.Lock())
await lock.acquire()
try: try:
# **critical section** that should prevent other tasks from # **critical section** that should prevent other tasks from
# checking the _Cache until complete otherwise the scheduler # checking the _Cache until complete otherwise the scheduler
@ -189,21 +194,21 @@ async def maybe_open_context(
# TODO: does this need to be a tractor "root nursery"? # TODO: does this need to be a tractor "root nursery"?
resources = _Cache.resources resources = _Cache.resources
assert not resources.get(ctx_key), f'Resource exists? {ctx_key}' assert not resources.get(ctx_key), f'Resource exists? {ctx_key}'
ln, _ = resources[ctx_key] = (service_n, trio.Event()) resources[ctx_key] = (service_n, trio.Event())
value = await ln.start( value = await service_n.start(
_Cache.run_ctx, _Cache.run_ctx,
mngr, mngr,
ctx_key, ctx_key,
) )
_Cache.users += 1 _Cache.users += 1
_Cache.lock.release() lock.release()
yield False, value yield False, value
else: else:
log.info(f'Reusing _Cached resource for {ctx_key}') log.info(f'Reusing _Cached resource for {ctx_key}')
_Cache.users += 1 _Cache.users += 1
_Cache.lock.release() lock.release()
yield True, value yield True, value
finally: finally:
@ -221,3 +226,5 @@ async def maybe_open_context(
if entry: if entry:
_, no_more_users = entry _, no_more_users = entry
no_more_users.set() no_more_users.set()
_Cache.locks.pop(fid)