Merge pull request #76 from freininghaus/fix-issue-75-out-of-memory

Use WeakKeyDictionary for caching types in is_future_like

promise/dataloader.py

@@ -73,7 +73,6 @@ def __init__(
             self.cache = cache
 
         self.get_cache_key = get_cache_key or (lambda x: x)
-
         self._promise_cache = cache_map or {}
         self._queue = []  # type: List[Loader]
         self._scheduler = scheduler

promise/promise.py

@@ -3,6 +3,7 @@
 from sys import version_info, exc_info
 from threading import RLock
 from types import TracebackType
+from weakref import WeakKeyDictionary
 
 from six import reraise  # type: ignore
 from .async_ import Async
@@ -34,6 +35,7 @@
         Union,
         Generic,
         Hashable,
+        MutableMapping,
     )
 
 
@@ -817,7 +819,7 @@ def is_thenable(cls, obj):
         )
 
 
-_type_done_callbacks = {}  # type: Dict[type, bool]
+_type_done_callbacks = WeakKeyDictionary()  # type: MutableMapping[type, bool]
 
 
 def is_future_like(_type):

tests/test_issues.py

@@ -2,6 +2,8 @@
 from concurrent.futures import ThreadPoolExecutor
 from promise import Promise
 import time
+import weakref
+import gc
 
 executor = ThreadPoolExecutor(max_workers=40000)
 
@@ -108,3 +110,23 @@ def do(x):
 
     p = Promise.resolve(None).then(do)
     assert p.get() == "ok"
+
+
+def test_issue_75():
+    def function_with_local_type():
+        class A:
+            pass
+
+        a = A()
+        assert a == Promise.resolve(a).get()
+
+        return weakref.ref(A)
+
+    weak_reference = function_with_local_type()
+
+    # The local type 'A' from the function is still kept alive by reference cycles.
+    gc.collect()
+
+    # Now the local type should have been garbage collected,
+    # such that the weak reference should be invalid.
+    assert not weak_reference()