gh-133485: Use interpreters.Interpreter in InterpreterPoolExecutor (gh-133957)

Most importantly, this resolves the issues with functions and types defined in __main__.
It also expands the number of supported objects and simplifies the implementation.

Doc/library/concurrent.futures.rst

@@ -265,7 +265,7 @@ Each worker's interpreter is isolated from all the other interpreters.
 "Isolated" means each interpreter has its own runtime state and
 operates completely independently.  For example, if you redirect
 :data:`sys.stdout` in one interpreter, it will not be automatically
-redirected any other interpreter.  If you import a module in one
+redirected to any other interpreter.  If you import a module in one
 interpreter, it is not automatically imported in any other.  You
 would need to import the module separately in interpreter where
 you need it.  In fact, each module imported in an interpreter is
@@ -287,7 +287,7 @@ efficient alternative is to serialize with :mod:`pickle` and then send
 the bytes over a shared :mod:`socket <socket>` or
 :func:`pipe <os.pipe>`.
 
-.. class:: InterpreterPoolExecutor(max_workers=None, thread_name_prefix='', initializer=None, initargs=(), shared=None)
+.. class:: InterpreterPoolExecutor(max_workers=None, thread_name_prefix='', initializer=None, initargs=())
 
    A :class:`ThreadPoolExecutor` subclass that executes calls asynchronously
    using a pool of at most *max_workers* threads.  Each thread runs
@@ -304,21 +304,10 @@ the bytes over a shared :mod:`socket <socket>` or
    and *initargs* using :mod:`pickle` when sending them to the worker's
    interpreter.
 
-   .. note::
-      Functions defined in the ``__main__`` module cannot be pickled
-      and thus cannot be used.
-
    .. note::
       The executor may replace uncaught exceptions from *initializer*
       with :class:`~concurrent.futures.interpreter.ExecutionFailed`.
 
-   The optional *shared* argument is a :class:`dict` of objects that all
-   interpreters in the pool share.  The *shared* items are added to each
-   interpreter's ``__main__`` module.  Not all objects are shareable.
-   Shareable objects include the builtin singletons, :class:`str`
-   and :class:`bytes`, and :class:`memoryview`.  See :pep:`734`
-   for more info.
-
    Other caveats from parent :class:`ThreadPoolExecutor` apply here.
 
 :meth:`~Executor.submit` and :meth:`~Executor.map` work like normal,
@@ -326,10 +315,6 @@ except the worker serializes the callable and arguments using
 :mod:`pickle` when sending them to its interpreter.  The worker
 likewise serializes the return value when sending it back.
 
-.. note::
-   Functions defined in the ``__main__`` module cannot be pickled
-   and thus cannot be used.
-
 When a worker's current task raises an uncaught exception, the worker
 always tries to preserve the exception as-is.  If that is successful
 then it also sets the ``__cause__`` to a corresponding

Lib/concurrent/futures/interpreter.py

@@ -1,56 +1,39 @@
 """Implements InterpreterPoolExecutor."""
 
-import contextlib
+from concurrent import interpreters
-import pickle
+import sys
 import textwrap
 from . import thread as _thread
-import _interpreters
+import traceback
-import _interpqueues
 
 
-class ExecutionFailed(_interpreters.InterpreterError):
+def do_call(results, func, args, kwargs):
-    """An unhandled exception happened during execution."""
+    try:
-
+        return func(*args, **kwargs)
-    def __init__(self, excinfo):
+    except BaseException as exc:
-        msg = excinfo.formatted
+        # Send the captured exception out on the results queue,
-        if not msg:
+        # but still leave it unhandled for the interpreter to handle.
-            if excinfo.type and excinfo.msg:
-                msg = f'{excinfo.type.__name__}: {excinfo.msg}'
-            else:
-                msg = excinfo.type.__name__ or excinfo.msg
-        super().__init__(msg)
-        self.excinfo = excinfo
-
-    def __str__(self):
         try:
-            formatted = self.excinfo.errdisplay
+            results.put(exc)
-        except Exception:
+        except interpreters.NotShareableError:
-            return super().__str__()
+            # The exception is not shareable.
-        else:
+            print('exception is not shareable:', file=sys.stderr)
-            return textwrap.dedent(f"""
+            traceback.print_exception(exc)
-{super().__str__()}
+            results.put(None)
-
+        raise  # re-raise
-Uncaught in the interpreter:
-
-{formatted}
-                """.strip())
 
 
 class WorkerContext(_thread.WorkerContext):
 
     @classmethod
-    def prepare(cls, initializer, initargs, shared):
+    def prepare(cls, initializer, initargs):
         def resolve_task(fn, args, kwargs):
             if isinstance(fn, str):
                 # XXX Circle back to this later.
                 raise TypeError('scripts not supported')
             else:
-                # Functions defined in the __main__ module can't be pickled,
-                # so they can't be used here.  In the future, we could possibly
-                # borrow from multiprocessing to work around this.
                 task = (fn, args, kwargs)
-                data = pickle.dumps(task)
+            return task
-            return data
 
         if initializer is not None:
             try:
@@ -62,68 +45,24 @@ class WorkerContext(_thread.WorkerContext):
         else:
             initdata = None
         def create_context():
-            return cls(initdata, shared)
+            return cls(initdata)
         return create_context, resolve_task
 
-    @classmethod
+    def __init__(self, initdata):
-    @contextlib.contextmanager
-    def _capture_exc(cls, resultsid):
-        try:
-            yield
-        except BaseException as exc:
-            # Send the captured exception out on the results queue,
-            # but still leave it unhandled for the interpreter to handle.
-            _interpqueues.put(resultsid, (None, exc))
-            raise  # re-raise
-
-    @classmethod
-    def _send_script_result(cls, resultsid):
-        _interpqueues.put(resultsid, (None, None))
-
-    @classmethod
-    def _call(cls, func, args, kwargs, resultsid):
-        with cls._capture_exc(resultsid):
-            res = func(*args or (), **kwargs or {})
-        # Send the result back.
-        with cls._capture_exc(resultsid):
-            _interpqueues.put(resultsid, (res, None))
-
-    @classmethod
-    def _call_pickled(cls, pickled, resultsid):
-        with cls._capture_exc(resultsid):
-            fn, args, kwargs = pickle.loads(pickled)
-        cls._call(fn, args, kwargs, resultsid)
-
-    def __init__(self, initdata, shared=None):
         self.initdata = initdata
-        self.shared = dict(shared) if shared else None
+        self.interp = None
-        self.interpid = None
+        self.results = None
-        self.resultsid = None
 
     def __del__(self):
-        if self.interpid is not None:
+        if self.interp is not None:
             self.finalize()
 
-    def _exec(self, script):
-        assert self.interpid is not None
-        excinfo = _interpreters.exec(self.interpid, script, restrict=True)
-        if excinfo is not None:
-            raise ExecutionFailed(excinfo)
-
     def initialize(self):
-        assert self.interpid is None, self.interpid
+        assert self.interp is None, self.interp
-        self.interpid = _interpreters.create(reqrefs=True)
+        self.interp = interpreters.create()
         try:
-            _interpreters.incref(self.interpid)
-
             maxsize = 0
-            self.resultsid = _interpqueues.create(maxsize)
+            self.results = interpreters.create_queue(maxsize)
-
-            self._exec(f'from {__name__} import WorkerContext')
-
-            if self.shared:
-                _interpreters.set___main___attrs(
-                                    self.interpid, self.shared, restrict=True)
 
             if self.initdata:
                 self.run(self.initdata)
@@ -132,53 +71,25 @@ class WorkerContext(_thread.WorkerContext):
             raise  # re-raise
 
     def finalize(self):
-        interpid = self.interpid
+        interp = self.interp
-        resultsid = self.resultsid
+        results = self.results
-        self.resultsid = None
+        self.results = None
-        self.interpid = None
+        self.interp = None
-        if resultsid is not None:
+        if results is not None:
-            try:
+            del results
-                _interpqueues.destroy(resultsid)
+        if interp is not None:
-            except _interpqueues.QueueNotFoundError:
+            interp.close()
-                pass
-        if interpid is not None:
-            try:
-                _interpreters.decref(interpid)
-            except _interpreters.InterpreterNotFoundError:
-                pass
 
     def run(self, task):
-        data = task
-        script = f'WorkerContext._call_pickled({data!r}, {self.resultsid})'
-
         try:
-            self._exec(script)
+            return self.interp.call(do_call, self.results, *task)
-        except ExecutionFailed as exc:
+        except interpreters.ExecutionFailed as wrapper:
-            exc_wrapper = exc
+            # Wait for the exception data to show up.
-        else:
+            exc = self.results.get()
-            exc_wrapper = None
+            if exc is None:
-
+                # The exception must have been not shareable.
-        # Return the result, or raise the exception.
-        while True:
-            try:
-                obj = _interpqueues.get(self.resultsid)
-            except _interpqueues.QueueNotFoundError:
                 raise  # re-raise
-            except _interpqueues.QueueError:
+            raise exc from wrapper
-                continue
-            except ModuleNotFoundError:
-                # interpreters._queues doesn't exist, which means
-                # QueueEmpty doesn't.  Act as though it does.
-                continue
-            else:
-                break
-        (res, exc), unboundop = obj
-        assert unboundop is None, unboundop
-        if exc is not None:
-            assert res is None, res
-            assert exc_wrapper is not None
-            raise exc from exc_wrapper
-        return res
 
 
 class BrokenInterpreterPool(_thread.BrokenThreadPool):
@@ -192,11 +103,11 @@ class InterpreterPoolExecutor(_thread.ThreadPoolExecutor):
     BROKEN = BrokenInterpreterPool
 
     @classmethod
-    def prepare_context(cls, initializer, initargs, shared):
+    def prepare_context(cls, initializer, initargs):
-        return WorkerContext.prepare(initializer, initargs, shared)
+        return WorkerContext.prepare(initializer, initargs)
 
     def __init__(self, max_workers=None, thread_name_prefix='',
-                 initializer=None, initargs=(), shared=None):
+                 initializer=None, initargs=()):
         """Initializes a new InterpreterPoolExecutor instance.
 
         Args:
@@ -206,8 +117,6 @@ class InterpreterPoolExecutor(_thread.ThreadPoolExecutor):
             initializer: A callable or script used to initialize
                 each worker interpreter.
             initargs: A tuple of arguments to pass to the initializer.
-            shared: A mapping of shareabled objects to be inserted into
-                each worker interpreter.
         """
         super().__init__(max_workers, thread_name_prefix,
-                         initializer, initargs, shared=shared)
+                         initializer, initargs)

Lib/test/test_concurrent_futures/test_init.py

@@ -20,6 +20,10 @@ INITIALIZER_STATUS = 'uninitialized'
 def init(x):
     global INITIALIZER_STATUS
     INITIALIZER_STATUS = x
+    # InterpreterPoolInitializerTest.test_initializer fails
+    # if we don't have a LOAD_GLOBAL.  (It could be any global.)
+    # We will address this separately.
+    INITIALIZER_STATUS
 
 def get_init_status():
     return INITIALIZER_STATUS

Lib/test/test_concurrent_futures/test_interpreter_pool.py

@@ -2,35 +2,78 @@ import asyncio
 import contextlib
 import io
 import os
-import pickle
+import sys
 import time
 import unittest
-from concurrent.futures.interpreter import (
+from concurrent.futures.interpreter import BrokenInterpreterPool
-    ExecutionFailed, BrokenInterpreterPool,
+from concurrent import interpreters
-)
 from concurrent.interpreters import _queues as queues
 import _interpreters
 from test import support
+from test.support import os_helper
+from test.support import script_helper
 import test.test_asyncio.utils as testasyncio_utils
 
 from .executor import ExecutorTest, mul
 from .util import BaseTestCase, InterpreterPoolMixin, setup_module
 
 
+WINDOWS = sys.platform.startswith('win')
+
+
+@contextlib.contextmanager
+def nonblocking(fd):
+    blocking = os.get_blocking(fd)
+    if blocking:
+        os.set_blocking(fd, False)
+    try:
+        yield
+    finally:
+        if blocking:
+            os.set_blocking(fd, blocking)
+
+
+def read_file_with_timeout(fd, nbytes, timeout):
+    with nonblocking(fd):
+        end = time.time() + timeout
+        try:
+            return os.read(fd, nbytes)
+        except BlockingIOError:
+            pass
+        while time.time() < end:
+            try:
+                return os.read(fd, nbytes)
+            except BlockingIOError:
+                continue
+        else:
+            raise TimeoutError('nothing to read')
+
+
+if not WINDOWS:
+    import select
+    def read_file_with_timeout(fd, nbytes, timeout):
+        r, _, _ = select.select([fd], [], [], timeout)
+        if fd not in r:
+            raise TimeoutError('nothing to read')
+        return os.read(fd, nbytes)
+
+
 def noop():
     pass
 
 
 def write_msg(fd, msg):
+    import os
     os.write(fd, msg + b'\0')
 
 
-def read_msg(fd):
+def read_msg(fd, timeout=10.0):
     msg = b''
-    while ch := os.read(fd, 1):
+    ch = read_file_with_timeout(fd, 1, timeout)
-        if ch == b'\0':
+    while ch != b'\0':
-            return msg
         msg += ch
+        ch = os.read(fd, 1)
+    return msg
 
 
 def get_current_name():
@@ -113,6 +156,38 @@ class InterpreterPoolExecutorTest(
         self.assertEqual(before, b'\0')
         self.assertEqual(after, msg)
 
+    def test_init_with___main___global(self):
+        # See https://github.com/python/cpython/pull/133957#issuecomment-2927415311.
+        text = """if True:
+            from concurrent.futures import InterpreterPoolExecutor
+
+            INITIALIZER_STATUS = 'uninitialized'
+
+            def init(x):
+                global INITIALIZER_STATUS
+                INITIALIZER_STATUS = x
+                INITIALIZER_STATUS
+
+            def get_init_status():
+                return INITIALIZER_STATUS
+
+            if __name__ == "__main__":
+                exe = InterpreterPoolExecutor(initializer=init,
+                                              initargs=('initialized',))
+                fut = exe.submit(get_init_status)
+                print(fut.result())  # 'initialized'
+                exe.shutdown(wait=True)
+                print(INITIALIZER_STATUS)  # 'uninitialized'
+           """
+        with os_helper.temp_dir() as tempdir:
+            filename = script_helper.make_script(tempdir, 'my-script', text)
+            res = script_helper.assert_python_ok(filename)
+        stdout = res.out.decode('utf-8').strip()
+        self.assertEqual(stdout.splitlines(), [
+            'initialized',
+            'uninitialized',
+        ])
+
     def test_init_closure(self):
         count = 0
         def init1():
@@ -121,10 +196,19 @@ class InterpreterPoolExecutorTest(
             nonlocal count
             count += 1
 
-        with self.assertRaises(pickle.PicklingError):
+        with contextlib.redirect_stderr(io.StringIO()) as stderr:
-            self.executor_type(initializer=init1)
+            with self.executor_type(initializer=init1) as executor:
-        with self.assertRaises(pickle.PicklingError):
+                fut = executor.submit(lambda: None)
-            self.executor_type(initializer=init2)
+        self.assertIn('NotShareableError', stderr.getvalue())
+        with self.assertRaises(BrokenInterpreterPool):
+            fut.result()
+
+        with contextlib.redirect_stderr(io.StringIO()) as stderr:
+            with self.executor_type(initializer=init2) as executor:
+                fut = executor.submit(lambda: None)
+        self.assertIn('NotShareableError', stderr.getvalue())
+        with self.assertRaises(BrokenInterpreterPool):
+            fut.result()
 
     def test_init_instance_method(self):
         class Spam:
@@ -132,26 +216,12 @@ class InterpreterPoolExecutorTest(
                 raise NotImplementedError
         spam = Spam()
 
-        with self.assertRaises(pickle.PicklingError):
+        with contextlib.redirect_stderr(io.StringIO()) as stderr:
-            self.executor_type(initializer=spam.initializer)
+            with self.executor_type(initializer=spam.initializer) as executor:
-
+                fut = executor.submit(lambda: None)
-    def test_init_shared(self):
+        self.assertIn('NotShareableError', stderr.getvalue())
-        msg = b'eggs'
+        with self.assertRaises(BrokenInterpreterPool):
-        r, w = self.pipe()
+            fut.result()
-        script = f"""if True:
-            import os
-            if __name__ != '__main__':
-                import __main__
-                spam = __main__.spam
-            os.write({w}, spam + b'\\0')
-            """
-
-        executor = self.executor_type(shared={'spam': msg})
-        fut = executor.submit(exec, script)
-        fut.result()
-        after = read_msg(r)
-
-        self.assertEqual(after, msg)
 
     @unittest.expectedFailure
     def test_init_exception_in_script(self):
@@ -178,8 +248,6 @@ class InterpreterPoolExecutorTest(
         stderr = stderr.getvalue()
         self.assertIn('ExecutionFailed: Exception: spam', stderr)
         self.assertIn('Uncaught in the interpreter:', stderr)
-        self.assertIn('The above exception was the direct cause of the following exception:',
-                      stderr)
 
     @unittest.expectedFailure
     def test_submit_script(self):
@@ -208,10 +276,14 @@ class InterpreterPoolExecutorTest(
             return spam
 
         executor = self.executor_type()
-        with self.assertRaises(pickle.PicklingError):
+
-            executor.submit(task1)
+        fut = executor.submit(task1)
-        with self.assertRaises(pickle.PicklingError):
+        with self.assertRaises(_interpreters.NotShareableError):
-            executor.submit(task2)
+            fut.result()
+
+        fut = executor.submit(task2)
+        with self.assertRaises(_interpreters.NotShareableError):
+            fut.result()
 
     def test_submit_local_instance(self):
         class Spam:
@@ -219,8 +291,9 @@ class InterpreterPoolExecutorTest(
                 self.value = True
 
         executor = self.executor_type()
-        with self.assertRaises(pickle.PicklingError):
+        fut = executor.submit(Spam)
-            executor.submit(Spam)
+        with self.assertRaises(_interpreters.NotShareableError):
+            fut.result()
 
     def test_submit_instance_method(self):
         class Spam:
@@ -229,8 +302,9 @@ class InterpreterPoolExecutorTest(
         spam = Spam()
 
         executor = self.executor_type()
-        with self.assertRaises(pickle.PicklingError):
+        fut = executor.submit(spam.run)
-            executor.submit(spam.run)
+        with self.assertRaises(_interpreters.NotShareableError):
+            fut.result()
 
     def test_submit_func_globals(self):
         executor = self.executor_type()
@@ -242,13 +316,14 @@ class InterpreterPoolExecutorTest(
 
     @unittest.expectedFailure
     def test_submit_exception_in_script(self):
+        # Scripts are not supported currently.
         fut = self.executor.submit('raise Exception("spam")')
         with self.assertRaises(Exception) as captured:
             fut.result()
         self.assertIs(type(captured.exception), Exception)
         self.assertEqual(str(captured.exception), 'spam')
         cause = captured.exception.__cause__
-        self.assertIs(type(cause), ExecutionFailed)
+        self.assertIs(type(cause), interpreters.ExecutionFailed)
         for attr in ('__name__', '__qualname__', '__module__'):
             self.assertEqual(getattr(cause.excinfo.type, attr),
                              getattr(Exception, attr))
@@ -261,7 +336,7 @@ class InterpreterPoolExecutorTest(
         self.assertIs(type(captured.exception), Exception)
         self.assertEqual(str(captured.exception), 'spam')
         cause = captured.exception.__cause__
-        self.assertIs(type(cause), ExecutionFailed)
+        self.assertIs(type(cause), interpreters.ExecutionFailed)
         for attr in ('__name__', '__qualname__', '__module__'):
             self.assertEqual(getattr(cause.excinfo.type, attr),
                              getattr(Exception, attr))
@@ -269,16 +344,93 @@ class InterpreterPoolExecutorTest(
 
     def test_saturation(self):
         blocker = queues.create()
-        executor = self.executor_type(4, shared=dict(blocker=blocker))
+        executor = self.executor_type(4)
 
         for i in range(15 * executor._max_workers):
-            executor.submit(exec, 'import __main__; __main__.blocker.get()')
+            executor.submit(blocker.get)
-            #executor.submit('blocker.get()')
         self.assertEqual(len(executor._threads), executor._max_workers)
         for i in range(15 * executor._max_workers):
             blocker.put_nowait(None)
         executor.shutdown(wait=True)
 
+    def test_blocking(self):
+        # There is no guarantee that a worker will be created for every
+        # submitted task.  That's because there's a race between:
+        #
+        # * a new worker thread, created when task A was just submitted,
+        #   becoming non-idle when it picks up task A
+        # * after task B is added to the queue, a new worker thread
+        #   is started only if there are no idle workers
+        #   (the check in ThreadPoolExecutor._adjust_thread_count())
+        #
+        # That means we must not block waiting for *all* tasks to report
+        # "ready" before we unblock the known-ready workers.
+        ready = queues.create()
+        blocker = queues.create()
+
+        def run(taskid, ready, blocker):
+            # There can't be any globals here.
+            ready.put_nowait(taskid)
+            blocker.get()  # blocking
+
+        numtasks = 10
+        futures = []
+        with self.executor_type() as executor:
+            # Request the jobs.
+            for i in range(numtasks):
+                fut = executor.submit(run, i, ready, blocker)
+                futures.append(fut)
+            pending = numtasks
+            while pending > 0:
+                # Wait for any to be ready.
+                done = 0
+                for _ in range(pending):
+                    try:
+                        ready.get(timeout=1)  # blocking
+                    except interpreters.QueueEmpty:
+                        pass
+                    else:
+                        done += 1
+                pending -= done
+                # Unblock the workers.
+                for _ in range(done):
+                    blocker.put_nowait(None)
+
+    def test_blocking_with_limited_workers(self):
+        # This is essentially the same as test_blocking,
+        # but we explicitly force a limited number of workers,
+        # instead of it happening implicitly sometimes due to a race.
+        ready = queues.create()
+        blocker = queues.create()
+
+        def run(taskid, ready, blocker):
+            # There can't be any globals here.
+            ready.put_nowait(taskid)
+            blocker.get()  # blocking
+
+        numtasks = 10
+        futures = []
+        with self.executor_type(4) as executor:
+            # Request the jobs.
+            for i in range(numtasks):
+                fut = executor.submit(run, i, ready, blocker)
+                futures.append(fut)
+            pending = numtasks
+            while pending > 0:
+                # Wait for any to be ready.
+                done = 0
+                for _ in range(pending):
+                    try:
+                        ready.get(timeout=1)  # blocking
+                    except interpreters.QueueEmpty:
+                        pass
+                    else:
+                        done += 1
+                pending -= done
+                # Unblock the workers.
+                for _ in range(done):
+                    blocker.put_nowait(None)
+
     @support.requires_gil_enabled("gh-117344: test is flaky without the GIL")
     def test_idle_thread_reuse(self):
         executor = self.executor_type()
@@ -289,12 +441,21 @@ class InterpreterPoolExecutorTest(
         executor.shutdown(wait=True)
 
     def test_pickle_errors_propagate(self):
-        # GH-125864: Pickle errors happen before the script tries to execute, so the
+        # GH-125864: Pickle errors happen before the script tries to execute,
-        # queue used to wait infinitely.
+        # so the queue used to wait infinitely.
-
         fut = self.executor.submit(PickleShenanigans(0))
-        with self.assertRaisesRegex(RuntimeError, "gotcha"):
+        expected = interpreters.NotShareableError
+        with self.assertRaisesRegex(expected, 'args not shareable') as cm:
             fut.result()
+        self.assertRegex(str(cm.exception.__cause__), 'unpickled')
+
+    def test_no_stale_references(self):
+        # Weak references don't cross between interpreters.
+        raise unittest.SkipTest('not applicable')
+
+    def test_free_reference(self):
+        # Weak references don't cross between interpreters.
+        raise unittest.SkipTest('not applicable')
 
 
 class AsyncioTest(InterpretersMixin, testasyncio_utils.TestCase):

Python/crossinterp.c

@@ -674,7 +674,9 @@ _PyPickle_Loads(struct _unpickle_context *ctx, PyObject *pickled)
 
 finally:
     if (exc != NULL) {
-        sync_module_capture_exc(tstate, &ctx->main);
+        if (_PyErr_Occurred(tstate)) {
+            sync_module_capture_exc(tstate, &ctx->main);
+        }
         // We restore the original exception.
         // It might make sense to chain it (__context__).
         _PyErr_SetRaisedException(tstate, exc);