Change logic for resizing stack; top_of_stack is now a Gen

Author: jdemeyer

cypari2/handle_error.pyx

@@ -29,7 +29,7 @@ from cysignals.signals cimport sig_block, sig_unblock, sig_error
 
 from .paridecl cimport *
 from .paripriv cimport *
-from .stack cimport clone_gen_noclear, reset_avma
+from .stack cimport clone_gen_noclear, reset_avma, after_resize
 
 
 # We derive PariError from RuntimeError, for backward compatibility with
@@ -222,9 +222,10 @@ cdef void _pari_err_recover(long errnum):
     reset_avma()
 
     # Special case errnum == -1 corresponds to a reallocation of the
-    # PARI stack. This is not an error, so just proceed as if nothing
-    # happened.
+    # PARI stack. This is not an error, so call after_resize() and
+    # proceed as if nothing happened.
     if errnum < 0:
+        after_resize()
         return
 
     # An exception was raised.  Jump to the signal-handling code

cypari2/pari_instance.pyx

@@ -287,8 +287,8 @@ from .string_utils cimport to_string, to_bytes
 from .paridecl cimport *
 from .paripriv cimport *
 from .gen cimport Gen, objtogen
-from .stack cimport (new_gen, new_gen_noclear,
-                     clear_stack, move_gens_to_heap)
+from .stack cimport (new_gen, new_gen_noclear, clear_stack,
+                     set_pari_stack_size, before_resize, after_resize)
 from .handle_error cimport _pari_init_error_handling
 from .closure cimport _pari_init_closure
 
@@ -472,16 +472,6 @@ cdef void python_flush():
 include 'auto_instance.pxi'
 
 
-cdef int set_pari_stack_size(size_t size, size_t sizemax) except -1:
-    """
-    Safely set the PARI stack size
-    """
-    move_gens_to_heap(-1)
-    sig_on()
-    paristack_setsize(size, sizemax)
-    sig_off()
-
-
 cdef class Pari(Pari_auto):
     def __cinit__(self):
         r"""
@@ -502,6 +492,7 @@ cdef class Pari(Pari_auto):
         # Take 1MB as minimal stack. Use maxprime=0, which PARI will
         # internally increase to some small value like 65537.
         pari_init_opts(1000000, 0, INIT_DFTm)
+        after_resize()
 
         # Disable PARI's stack overflow checking which is incompatible
         # with multi-threading.
@@ -1413,21 +1404,19 @@ cdef long get_var(v) except -2:
     return varno
 
 
-# Monkey-patched versions of default(parisize) and default(parisizemax).
-# We need to call move_gens_to_heap(-1) before reallocating the PARI
-# stack. The monkey-patching is set up in PariInstance.__cinit__
+# Monkey-patched versions of default(parisize) and default(parisizemax)
+# which call before_resize() and after_resize().
+# The monkey-patching is set up in PariInstance.__cinit__
 cdef GEN patched_parisize(const char* v, long flag):
-    try:
-        move_gens_to_heap(-1)
-    except:
+    # Cast to int(*)() to avoid exception handling
+    if (<int(*)()>before_resize)():
         sig_error()
     return sd_parisize(v, flag)
 
 
 cdef GEN patched_parisizemax(const char* v, long flag):
-    try:
-        move_gens_to_heap(-1)
-    except:
+    # Cast to int(*)() to avoid exception handling
+    if (<int(*)()>before_resize)():
         sig_error()
     return sd_parisizemax(v, flag)
 

cypari2/stack.pxd

@@ -14,6 +14,10 @@ cdef void reset_avma()
 cdef void remove_from_pari_stack(Gen self)
 cdef int move_gens_to_heap(pari_sp lim) except -1
 
+cdef int before_resize() except -1
+cdef int set_pari_stack_size(size_t size, size_t sizemax) except -1
+cdef void after_resize()
+
 
 cdef class DetachGen:
     cdef source

cypari2/stack.pyx

@@ -27,7 +27,8 @@ from cysignals.memory cimport check_malloc, sig_free
 from .gen cimport Gen, Gen_new
 from .paridecl cimport (avma, pari_mainstack, gnil, gcopy,
                         is_universal_constant, is_on_stack,
-                        isclone, gclone, gclone_refc)
+                        isclone, gclone, gclone_refc,
+                        paristack_setsize)
 
 from warnings import warn
 
@@ -38,7 +39,7 @@ cdef extern from *:
 
 
 # Singleton object to denote the top of the PARI stack
-cdef object top_of_stack = object()
+cdef Gen top_of_stack = Gen_new(gnil, NULL)
 
 # Pointer to the Gen on the bottom of the PARI stack. This is the first
 # element of the Gen linked list. If the linked list is empty, this
@@ -84,11 +85,10 @@ cdef inline Gen Gen_stack_new(GEN x):
     z = Gen_new(x, <GEN>avma)
     z.next = n
     stackbottom = <PyObject*>z
-    if n is not top_of_stack:
-        sz = z.sp()
-        sn = n.sp()
-        if sz > sn:
-            raise SystemError(f"objects on PARI stack in invalid order (first: 0x{sz:x}; next: 0x{sn:x})")
+    sz = z.sp()
+    sn = n.sp()
+    if sz > sn:
+        raise SystemError(f"objects on PARI stack in invalid order (first: 0x{sz:x}; next: 0x{sn:x})")
     return z
 
 
@@ -102,10 +102,7 @@ cdef void reset_avma():
     # NOTE: this can be called with an exception set (the error handler
     # does that)!
     global avma
-    if stackbottom is <PyObject*>top_of_stack:
-        avma = pari_mainstack.top
-    else:
-        avma = (<Gen>stackbottom).sp()
+    avma = (<Gen>stackbottom).sp()
 
 
 cdef void clear_stack():
@@ -142,6 +139,35 @@ cdef int move_gens_to_heap(pari_sp lim) except -1:
         current.address = current.g
 
 
+cdef int before_resize() except -1:
+    """
+    Prepare for resizing the PARI stack
+
+    This must be called before reallocating the PARI stack
+    """
+    move_gens_to_heap(-1)
+    if top_of_stack.sp() != pari_mainstack.top:
+        raise RuntimeError("cannot resize PARI stack here")
+
+
+cdef int set_pari_stack_size(size_t size, size_t sizemax) except -1:
+    """
+    Safely set the PARI stack size
+    """
+    before_resize()
+    sig_on()
+    paristack_setsize(size, sizemax)
+    sig_off()
+    after_resize()
+
+
+cdef void after_resize():
+    """
+    This must be called after reallocating the PARI stack
+    """
+    top_of_stack.address = <GEN>pari_mainstack.top
+
+
 cdef Gen new_gen(GEN x):
     """
     Create a new ``Gen`` from a ``GEN``. Except if `x` is ``gnil``, then