Avoid retaining evaluate out arrays

RELEASE_NOTES.rst

@@ -6,6 +6,7 @@ Changes from 2.14.1 to 2.14.2
 -----------------------------
 
 * **Under development.**
+* Avoid keeping arrays passed as ``out=`` alive in the ``re_evaluate`` cache.
 
 Changes from 2.14.0 to 2.14.1
 -----------------------------

numexpr/necompiler.py

@@ -14,6 +14,7 @@
 import re
 import sys
 import threading
+import weakref
 from typing import Dict, Optional
 
 import numpy
@@ -794,6 +795,26 @@ def getArguments(names, local_dict=None, global_dict=None, _frame_depth: int=2):
 evaluate_lock = threading.Lock()
 
 
+def _cache_last_kwargs(out: numpy.ndarray,
+                       order: str,
+                       casting: str,
+                       ex_uses_vml: bool) -> Dict:
+    return {
+        'out': None if out is None else weakref.ref(out),
+        'order': order,
+        'casting': casting,
+        'ex_uses_vml': ex_uses_vml,
+    }
+
+
+def _resolve_last_kwargs(kwargs: Dict) -> Dict:
+    kwargs = kwargs.copy()
+    out = kwargs.get('out')
+    if isinstance(out, weakref.ReferenceType):
+        kwargs['out'] = out()
+    return kwargs
+
+
 def validate(ex: str,
              local_dict: Optional[Dict] = None,
              global_dict: Optional[Dict] = None,
@@ -905,8 +926,7 @@ def validate(ex: str,
             compiled_ex = _numexpr_cache.c[numexpr_key]
         except KeyError:
             compiled_ex = _numexpr_cache.c[numexpr_key] = NumExpr(ex, signature, sanitize=sanitize, **context)
-        kwargs = {'out': out, 'order': order, 'casting': casting,
-                  'ex_uses_vml': ex_uses_vml}
+        kwargs = _cache_last_kwargs(out, order, casting, ex_uses_vml)
         _numexpr_last.l.set(ex=compiled_ex, argnames=names, kwargs=kwargs)
     except Exception as e:
         return e
@@ -1049,6 +1069,6 @@ def re_evaluate(local_dict: Optional[Dict] = None,
         raise RuntimeError("A previous evaluate() execution was not found, please call `validate` or `evaluate` once before `re_evaluate`")
     argnames = _numexpr_last.l['argnames']
     args = getArguments(argnames, local_dict, global_dict, _frame_depth=_frame_depth)
-    kwargs = _numexpr_last.l['kwargs']
+    kwargs = _resolve_last_kwargs(_numexpr_last.l['kwargs'])
     # with evaluate_lock:
     return compiled_ex(*args, **kwargs)

numexpr/tests/test_numexpr.py

@@ -9,13 +9,14 @@
 #  rights to use.
 ####################################################################
 
-
+import gc
 import os
 import platform
 import subprocess
 import sys
 import unittest
 import warnings
+import weakref
 from contextlib import contextmanager
 from unittest.mock import MagicMock
 
@@ -412,6 +413,30 @@ def test_re_evaluate_dict(self):
         x = re_evaluate(local_dict=local_dict)
         assert_array_equal(x, array([86., 124., 168.]))
 
+    def test_evaluate_out_is_not_kept_alive(self):
+        a = arange(1000.0)
+        out = zeros(a.shape)
+        out_ref = weakref.ref(out)
+
+        evaluate("a + 1", local_dict={"a": a}, out=out)
+        del out
+        gc.collect()
+
+        assert out_ref() is None
+
+    def test_re_evaluate_reuses_live_out(self):
+        a = array([1., 2., 3.])
+        out = zeros(a.shape)
+
+        x = evaluate("a + 1", local_dict={"a": a}, out=out)
+        assert x is out
+        assert_array_equal(out, array([2., 3., 4.]))
+
+        a = array([4., 5., 6.])
+        x = re_evaluate(local_dict={"a": a})
+        assert x is out
+        assert_array_equal(out, array([5., 6., 7.]))
+
     def test_validate(self):
         a = array([1., 2., 3.])
         b = array([4., 5., 6.])