use stopit to implement TimeConstrained (#1177)

If this works, maybe we can simplify the implementation of
`TimeConstrained

Author: mmatera

mathics/builtin/datentime.py

@@ -27,11 +27,7 @@
 from mathics.core.convert.expression import to_expression, to_mathics_list
 from mathics.core.convert.python import from_python
 from mathics.core.element import ImmutableValueMixin
-from mathics.core.evaluation import (
-    Evaluation,
-    TimeoutInterrupt,
-    run_with_timeout_and_stack,
-)
+from mathics.core.evaluation import Evaluation
 from mathics.core.expression import Expression
 from mathics.core.list import ListExpression
 from mathics.core.symbols import Symbol
@@ -1070,6 +1066,7 @@ def evaluate(self, evaluation):
 
 
 if sys.platform != "emscripten":
+    import stopit
 
     class TimeConstrained(Builtin):
         """
@@ -1111,18 +1108,22 @@ def eval_3(self, expr, t, failexpr, evaluation):
                 evaluation.message("TimeConstrained", "timc", t)
                 return
             try:
-                t = float(t.to_python())
-                evaluation.timeout_queue.append((t, datetime.now().timestamp()))
+                timeout = float(t.to_python())
+                evaluation.timeout_queue.append((timeout, datetime.now().timestamp()))
                 request = lambda: expr.evaluate(evaluation)
-                res = run_with_timeout_and_stack(request, t, evaluation)
-            except TimeoutInterrupt:
-                evaluation.timeout_queue.pop()
-                return failexpr.evaluate(evaluation)
+                done = False
+                with stopit.ThreadingTimeout(timeout) as to_ctx_mgr:
+                    assert to_ctx_mgr.state == to_ctx_mgr.EXECUTING
+                    result = request()
+                    done = True
+                if done:
+                    evaluation.timeout_queue.pop()
+                    return result
             except Exception:
                 evaluation.timeout_queue.pop()
                 raise
             evaluation.timeout_queue.pop()
-            return res
+            return failexpr.evaluate(evaluation)
 
 
 class TimeZone(Predefined):

mathics/core/evaluation.py

@@ -4,8 +4,6 @@
 import sys
 import time
 from abc import ABC
-from queue import Queue
-from threading import Thread, stack_size as set_thread_stack_size
 from typing import Any, Callable, Dict, List, Optional, Tuple, Union, overload
 
 from mathics_scanner import TranslateError
@@ -57,16 +55,6 @@
 SymbolPrePrint = Symbol("System`$PrePrint")
 SymbolPost = Symbol("System`$Post")
 
-
-def _thread_target(request, queue) -> None:
-    try:
-        result = request()
-        queue.put((True, result))
-    except BaseException:
-        exc_info = sys.exc_info()
-        queue.put((False, exc_info))
-
-
 # MAX_RECURSION_DEPTH gives the maximum value allowed for $RecursionLimit. it's usually set to its
 # default settings.DEFAULT_MAX_RECURSION_DEPTH.
 
@@ -96,54 +84,6 @@ def set_python_recursion_limit(n) -> None:
         raise OverflowError
 
 
-def run_with_timeout_and_stack(request, timeout, evaluation):
-    """
-    interrupts evaluation after a given time period. Provides a suitable stack environment.
-    """
-
-    # only use set_thread_stack_size if max recursion depth was changed via the environment variable
-    # MATHICS_MAX_RECURSION_DEPTH. if it is set, we always use a thread, even if timeout is None, in
-    # order to be able to set the thread stack size.
-
-    if MAX_RECURSION_DEPTH > settings.DEFAULT_MAX_RECURSION_DEPTH:
-        set_thread_stack_size(python_stack_size(MAX_RECURSION_DEPTH))
-    elif timeout is None:
-        return request()
-
-    queue = Queue(maxsize=1)  # stores the result or exception
-    thread = Thread(target=_thread_target, args=(request, queue))
-    thread.start()
-
-    # Thead join(timeout) can leave zombie threads (we are the parent)
-    # when a time out occurs, but the thread hasn't terminated.  See
-    # https://docs.python.org/3/library/multiprocessing.shared_memory.html
-    # for a detailed discussion of this.
-    #
-    # To reduce this problem, we make use of specific properties of
-    # the Mathics3 evaluator: if we set "evaluation.timeout", the
-    # next call to "Expression.evaluate" in the thread will finish it
-    # immediately.
-    #
-    # However this still will not terminate long-running processes
-    # in Sympy or or libraries called by Mathics3 that might hang or run
-    # for a long time.
-    thread.join(timeout)
-    if thread.is_alive():
-        evaluation.timeout = True
-        while thread.is_alive():
-            time.sleep(0.001)
-            pass
-        evaluation.timeout = False
-        evaluation.stopped = False
-        raise TimeoutInterrupt()
-
-    success, result = queue.get()
-    if success:
-        return result
-    else:
-        raise result[1].with_traceback(result[2])
-
-
 class _Out(KeyComparable):
     def __init__(self) -> None:
         self.is_message = False
@@ -296,7 +236,7 @@ def evaluate():
 
         try:
             try:
-                result = run_with_timeout_and_stack(evaluate, timeout, self)
+                result = evaluate()
             except KeyboardInterrupt:
                 if self.catch_interrupt:
                     self.exc_result = SymbolAborted

mathics/eval/sympy.py

@@ -2,9 +2,6 @@
 Evaluation of SymPy functions
 """
 
-import sys
-from queue import Queue
-from threading import Thread
 from typing import Optional
 
 import sympy
@@ -15,9 +12,7 @@
 from mathics.core.evaluation import Evaluation
 
 
-def eval_sympy_unconstrained(
-    self, z: BaseElement, evaluation: Evaluation
-) -> Optional[BaseElement]:
+def eval_sympy(self, z: BaseElement, evaluation: Evaluation) -> Optional[BaseElement]:
     """
     Evaluate element `z` converting it to SymPy and back to Mathics3.
     If an exception is raised we return None.
@@ -33,52 +28,3 @@ def eval_sympy_unconstrained(
         return from_sympy(tracing.run_sympy(sympy_fn, *sympy_args))
     except Exception:
         return
-
-
-def eval_sympy_with_timeout(
-    self, z: BaseElement, evaluation: Evaluation
-) -> Optional[BaseElement]:
-    """
-    Evaluate an element `z` converting it to SymPy,
-    and back to Mathics3.
-    If an exception is raised we return None.
-
-    This version is run in a thread, and checked for evaluation timeout.
-    """
-
-    if evaluation.timeout is None:
-        return eval_sympy_unconstrained(self, z, evaluation)
-
-    def _thread_target(queue) -> None:
-        try:
-            result = eval_sympy_unconstrained(self, z, evaluation)
-            queue.put((True, result))
-        except BaseException:
-            exc_info = sys.exc_info()
-            queue.put((False, exc_info))
-
-    queue = Queue(maxsize=1)  # stores the result or exception
-
-    thread = Thread(target=_thread_target, args=(queue,))
-    thread.start()
-    while thread.is_alive():
-        thread.join(0.001)
-        if evaluation.timeout:
-            # I can kill the thread.
-            # just leave it...
-            return None
-
-    # pick the result and return
-    success, result = queue.get()
-    if success:
-        return result
-    else:
-        raise result[1].with_traceback(result[2])
-
-
-# Common top-level evaluation SymPy "eval" function:
-eval_sympy = (
-    eval_sympy_unconstrained
-    if sys.platform in ("emscripten",)
-    else eval_sympy_with_timeout
-)

pyproject.toml

@@ -18,6 +18,7 @@ dependencies = [
     # Pillow 9.1.0 supports BigTIFF with big-endian byte order.
     # ExampleData image hedy.tif is in this format.
     # Pillow 9.2 handles sunflowers.jpg
+    "stopit; platform_system != 'Emscripten'",
     "pillow >= 9.2",
     "pint",
     "python-dateutil",