[RLlib] Solve PyTorch/TF-eager A3C async race condition between calling model and its value function. (#13467)

rllib/utils/threading.py

@@ -0,0 +1,27 @@
+from typing import Callable
+
+
+def with_lock(func: Callable):
+    """Use as decorator (@withlock) around object methods that need locking.
+
+    Note: The object must have a self._lock = threading.Lock() property.
+    Locking thus works on the object level (no two locked methods of the same
+    object can be called asynchronously).
+
+    Args:
+        func (Callable): The function to decorate/wrap.
+
+    Returns:
+        Callable: The wrapped (object-level locked) function.
+    """
+
+    def wrapper(self, *a, **k):
+        try:
+            with self._lock:
+                return func(self, *a, **k)
+        except AttributeError:
+            raise AttributeError(
+                "Object {} must have a `self._lock` property (assigned to a "
+                "threading.Lock() object in its constructor)!".format(self))
+
+    return wrapper