refcount libsingular rings used in plural

src/sage/libs/singular/ring.pyx

@@ -446,12 +446,14 @@ cdef ring *singular_ring_reference(ring *existing_ring) except NULL:
 
     INPUT:
 
-    - ``existing_ring`` -- an existing Singular ring.
+    - ``existing_ring`` -- a Singular ring.
 
     OUTPUT:
 
-    The same ring with its refcount increased. After calling this
-    function `n` times, you need to call :func:`singular_ring_delete`
+    The same ring with its refcount increased. If ``existing_ring``
+    has not been refcounted yet, it will be after calling this function.
+    If initially ``existing_ring`` was refcounted once, then after
+    calling this function `n` times, you need to call :func:`singular_ring_delete`
     `n+1` times to actually deallocate the ring.
 
     EXAMPLE::
@@ -487,8 +489,7 @@ cdef ring *singular_ring_reference(ring *existing_ring) except NULL:
     if existing_ring==NULL:
         raise ValueError('singular_ring_reference(ring*) called with NULL pointer.')
     cdef object r = wrap_ring(existing_ring)
-    refcount = ring_refcount_dict.pop(r)
-    ring_refcount_dict[r] = refcount+1
+    ring_refcount_dict[r] = ring_refcount_dict.get(r,0)+1
     return existing_ring
 
 

src/sage/rings/polynomial/plural.pyx

@@ -114,7 +114,7 @@ from sage.libs.singular.function cimport RingWrap
 from sage.libs.singular.polynomial cimport (singular_polynomial_call, singular_polynomial_cmp, singular_polynomial_add, singular_polynomial_sub, singular_polynomial_neg, singular_polynomial_pow, singular_polynomial_mul, singular_polynomial_rmul, singular_polynomial_deg, singular_polynomial_str_with_changed_varnames, singular_polynomial_latex, singular_polynomial_str, singular_polynomial_div_coeff)
 
 import sage.libs.singular.ring
-from sage.libs.singular.ring cimport singular_ring_new, singular_ring_delete, wrap_ring
+from sage.libs.singular.ring cimport singular_ring_new, singular_ring_delete, wrap_ring, singular_ring_reference
 
 from sage.libs.singular.singular cimport si2sa, sa2si, overflow_check
 
@@ -327,7 +327,7 @@ cdef class NCPolynomialRing_plural(Ring):
         cdef RingWrap rw = ncalgebra(self._c, self._d, ring = P)
 
         #       rw._output()
-        self._ring = rw._ring
+        self._ring = singular_ring_reference(rw._ring)
         self._ring.ShortOut = 0
 
         self.__ngens = n