From 66f1d915410a079dbb462f08f85edd2c342a8b8f Mon Sep 17 00:00:00 2001
From: Tyler Goodlet <jgbt@protonmail.com>
Date: Mon, 9 Aug 2021 19:27:42 -0400
Subject: [PATCH] Let's abstractify:  ->

---
 piker/_cacheables.py   | 46 +++++++++++++++++++-----------------------
 piker/clearing/_ems.py | 14 ++++++++-----
 2 files changed, 30 insertions(+), 30 deletions(-)

diff --git a/piker/_cacheables.py b/piker/_cacheables.py
index 1b756f8f..be1934ca 100644
--- a/piker/_cacheables.py
+++ b/piker/_cacheables.py
@@ -19,7 +19,7 @@ Cacheing apis and toolz.
 
 """
 from collections import OrderedDict
-from typing import Optional
+from typing import Optional, Hashable, TypeVar, AsyncContextManager
 from contextlib import (
     asynccontextmanager,
     AsyncExitStack,
@@ -30,10 +30,10 @@ import trio
 
 from .brokers import get_brokermod
 from .log import get_logger
-from . import data
 from .data.feed import Feed
 
 
+T = TypeVar('T')
 log = get_logger(__name__)
 
 
@@ -69,16 +69,17 @@ def async_lifo_cache(maxsize=128):
 _cache: dict[str, 'Client'] = {}  # noqa
 
 
+# XXX: this mis mostly an alt-implementation of
+# maybe_open_ctx() below except it uses an async exit statck.
+# ideally wer pick one or the other.
 @asynccontextmanager
 async def open_cached_client(
     brokername: str,
-    *args,
-    **kwargs,
 ) -> 'Client':  # noqa
-    """Get a cached broker client from the current actor's local vars.
+    '''Get a cached broker client from the current actor's local vars.
 
     If one has not been setup do it and cache it.
-    """
+    '''
     global _cache
 
     clients = _cache.setdefault('clients', {'_lock': trio.Lock()})
@@ -128,25 +129,27 @@ class cache:
     '''
     lock = trio.Lock()
     users: int = 0
-    feeds: dict[tuple[str, str], Feed] = {}
+    ctxs: dict[tuple[str, str], Feed] = {}
     no_more_users: Optional[trio.Event] = None
 
 
 @asynccontextmanager
-async def maybe_open_feed(
+async def maybe_open_ctx(
 
-    broker: str,
-    symbol: str,
+    key: Hashable,
+    mngr: AsyncContextManager[T],
     loglevel: str,
 
-) -> Feed:
-
-    key = (broker, symbol)
+) -> T:
+    '''Maybe open a context manager if there is not already a cached
+    version for the provided ``key``. Return the cached instance on
+    a cache hit.
 
+    '''
     @contextmanager
     def get_and_use() -> Feed:
         # key error must bubble here
-        feed = cache.feeds[key]
+        feed = cache.ctxs[key]
         log.info(f'Reusing cached feed for {key}')
         try:
             cache.users += 1
@@ -174,22 +177,15 @@ async def maybe_open_feed(
             # **critical section** that should prevent other tasks from
             # checking the cache until complete otherwise the scheduler
             # may switch and by accident we create more then one feed.
-
             cache.no_more_users = trio.Event()
 
             log.info(f'Allocating new feed for {key}')
             # TODO: eventually support N-brokers
-            async with (
-                data.open_feed(
-                    broker,
-                    [symbol],
-                    loglevel=loglevel,
-                ) as feed,
-            ):
-                cache.feeds[key] = feed
+            async with mngr as value:
+                cache.ctxs[key] = value
                 cache.lock.release()
                 try:
-                    yield feed
+                    yield value
                 finally:
                     # don't tear down the feed until there are zero
                     # users of it left.
@@ -197,4 +193,4 @@ async def maybe_open_feed(
                         await cache.no_more_users.wait()
 
                     log.warning('De-allocating feed for {key}')
-                    cache.feeds.pop(key)
+                    cache.ctxs.pop(key)
diff --git a/piker/clearing/_ems.py b/piker/clearing/_ems.py
index ad5c6cf4..06536859 100644
--- a/piker/clearing/_ems.py
+++ b/piker/clearing/_ems.py
@@ -32,9 +32,9 @@ import tractor
 
 from ..log import get_logger
 from ..data._normalize import iterticks
-from ..data.feed import Feed
+from ..data.feed import Feed, open_feed
 from .._daemon import maybe_spawn_brokerd
-from .._cacheables import maybe_open_feed
+from .._cacheables import maybe_open_ctx
 from . import _paper_engine as paper
 from ._messages import (
     Status, Order,
@@ -959,9 +959,13 @@ async def _emsd_main(
 
     # spawn one task per broker feed
     async with (
-        maybe_open_feed(
-            broker,
-            symbol,
+        maybe_open_ctx(
+            key=(broker, symbol),
+            mngr=open_feed(
+                broker,
+                [symbol],
+                loglevel=loglevel,
+            ),
             loglevel=loglevel,
         ) as feed,
     ):