Issue #11161: Update the documentation for ProcessPoolExecutor to note that it will not work in the interactive shell.
diff --git a/Doc/library/concurrent.futures.rst b/Doc/library/concurrent.futures.rst
index c2f92b3..93538e4 100644
--- a/Doc/library/concurrent.futures.rst
+++ b/Doc/library/concurrent.futures.rst
@@ -164,6 +164,9 @@
allows it to side-step the :term:`Global Interpreter Lock` but also means that
only picklable objects can be executed and returned.
+The ``__main__`` module must be importable by worker subprocesses. This means
+that :class:`ProcessPoolExecutor` will not work in the interactive interpreter.
+
Calling :class:`Executor` or :class:`Future` methods from a callable submitted
to a :class:`ProcessPoolExecutor` will result in deadlock.