MAINT: Improve memory usage in PEP3118 format parsing

Previously a local `Stream` class would be defined every time a format needed parsing.
Classes in cpython create reference cycles, which create load on the GC.

This may or may not resolve gh-6511

1 files changed, 20 insertions, 0 deletions

diff --git a/numpy/tests/test_ctypeslib.py b/numpy/tests/test_ctypeslib.py
index 75ce9c8ca..62793a9d6 100644
--- a/numpy/tests/test_ctypeslib.py
+++ b/numpy/tests/test_ctypeslib.py
@@ -170,3 +170,23 @@ class TestAsArray(object):
         check(as_array(pointer(c_array), shape=()))
         check(as_array(pointer(c_array[0]), shape=(2,)))
         check(as_array(pointer(c_array[0][0]), shape=(2, 3)))
+
+    def test_reference_cycles(self):
+        # related to gh-6511
+        import ctypes
+
+        # create array to work with
+        # don't use int/long to avoid running into bpo-10746
+        N = 100
+        a = np.arange(N, dtype=np.short)
+
+        # get pointer to array
+        pnt = np.ctypeslib.as_ctypes(a)
+
+        with np.testing.assert_no_gc_cycles():
+            # decay the array above to a pointer to its first element
+            newpnt = ctypes.cast(pnt, ctypes.POINTER(ctypes.c_short))
+            # and construct an array using this data
+            b = np.ctypeslib.as_array(newpnt, (N,))
+            # now delete both, which should cleanup both objects
+            del newpnt, b