Tidy up stable logic a little

Author: jonathanhogg

src/flitter/engine/control.py

@@ -13,7 +13,7 @@
 from .. import setproctitle
 from ..cache import SharedCache
 from ..clock import BeatCounter, system_clock
-from ..language.vm import log_vm_stats, ProgramInvalid
+from ..language.vm import log_vm_stats, StableChanged
 from ..model import Vector, StateDict, Context, null, numbers_cache_counts, empty_numbers_cache
 from ..plugins import get_plugin
 from ..render.window.models import Model
@@ -195,20 +195,27 @@ async def run(self):
                     run_program = current_program = program
                     self.handle_pragmas(program.pragmas, frame_time)
                     errors = logs = None
+                    stables = set()
+                    stable_cache = {}
 
                 now = system_clock()
                 housekeeping += now
                 execution -= now
 
                 if run_program is not None:
-                    context = Context(names={key: Vector.coerce(value) for key, value in dynamic.items()},
-                                      state=self.state, references=self._references, stables=stables, stable_cache=stable_cache)
-                    try:
-                        run_program.run(context, record_stats=self.vm_stats)
-                    except ProgramInvalid:
-                        logger.debug("Simplified program invalidated due to change of stable value")
-                        run_program = current_program
-                        run_program.run(context, record_stats=self.vm_stats)
+                    while True:
+                        context = Context(names={key: Vector.coerce(value) for key, value in dynamic.items()},
+                                          state=self.state, references=self._references, stables=stables, stable_cache=stable_cache)
+                        try:
+                            run_program.run(context, record_stats=self.vm_stats)
+                        except StableChanged as exc:
+                            if run_program is not current_program:
+                                logger.debug("Simplified program invalidated due to change of stable value")
+                                run_program = current_program
+                            else:
+                                raise RuntimeError("Compiled program contains unexpected StableAssert") from exc
+                        else:
+                            break
                 else:
                     context = Context()
 

src/flitter/language/vm.pyx

@@ -251,6 +251,10 @@ class ProgramInvalid(Exception):
     pass
 
 
+class StableChanged(ProgramInvalid):
+    pass
+
+
 cdef class VectorStack:
     def __cinit__(self, int64_t size=DEFAULT_STACK_SIZE, int64_t max_size=MAX_STACK_SIZE):
         self.vectors = <PyObject**>PyMem_Malloc(sizeof(PyObject*) * size)
@@ -1485,7 +1489,7 @@ cdef class Program:
                     if objptr == NULL or r1.eq(<Vector>objptr) is false_:
                         PyDict_SetItem(context.stable_cache, key, r1)
                         context.stables.remove(key)
-                        raise ProgramInvalid("Stable assertion failed")
+                        raise StableChanged(key)
 
                 elif instruction.code == OpCode.StableTest:
                     r1 = peek(stack)