From 20efceb75790f2a40fad449fd92a6b3d8fe40c8b Mon Sep 17 00:00:00 2001
From: Brian Quinlan <brian@sweetapp.com>
Date: Sat, 17 May 2014 13:51:10 -0700
Subject: Issue #21362: concurrent.futures does not validate that max_workers
 is proper

---
 Doc/library/concurrent.futures.rst  | 2 ++
 Lib/concurrent/futures/process.py   | 3 +++
 Lib/concurrent/futures/thread.py    | 3 +++
 Lib/test/test_concurrent_futures.py | 7 +++++++
 4 files changed, 15 insertions(+)

diff --git a/Doc/library/concurrent.futures.rst b/Doc/library/concurrent.futures.rst
index 0495737..08c926a 100644
--- a/Doc/library/concurrent.futures.rst
+++ b/Doc/library/concurrent.futures.rst
@@ -175,6 +175,8 @@ to a :class:`ProcessPoolExecutor` will result in deadlock.
    An :class:`Executor` subclass that executes calls asynchronously using a pool
    of at most *max_workers* processes.  If *max_workers* is ``None`` or not
    given, it will default to the number of processors on the machine.
+   If *max_workers* is lower or equal to ``0``, then a :exc:`ValueError`
+   will be raised.
 
    .. versionchanged:: 3.3
       When one of the worker processes terminates abruptly, a
diff --git a/Lib/concurrent/futures/process.py b/Lib/concurrent/futures/process.py
index 07b5225..1299390 100644
--- a/Lib/concurrent/futures/process.py
+++ b/Lib/concurrent/futures/process.py
@@ -334,6 +334,9 @@ class ProcessPoolExecutor(_base.Executor):
         if max_workers is None:
             self._max_workers = os.cpu_count() or 1
         else:
+            if max_workers <= 0:
+                raise ValueError("max_workers must be greater than 0")
+
             self._max_workers = max_workers
 
         # Make the call queue slightly larger than the number of processes to
diff --git a/Lib/concurrent/futures/thread.py b/Lib/concurrent/futures/thread.py
index f9beb0f..8d6081c 100644
--- a/Lib/concurrent/futures/thread.py
+++ b/Lib/concurrent/futures/thread.py
@@ -87,6 +87,9 @@ class ThreadPoolExecutor(_base.Executor):
             max_workers: The maximum number of threads that can be used to
                 execute the given calls.
         """
+        if max_workers <= 0:
+            raise ValueError("max_workers must be greater than 0")
+
         self._max_workers = max_workers
         self._work_queue = queue.Queue()
         self._threads = set()
diff --git a/Lib/test/test_concurrent_futures.py b/Lib/test/test_concurrent_futures.py
index c74b2ca..55254b5 100644
--- a/Lib/test/test_concurrent_futures.py
+++ b/Lib/test/test_concurrent_futures.py
@@ -425,6 +425,13 @@ class ExecutorTest:
         self.assertTrue(collected,
                         "Stale reference not collected within timeout.")
 
+    def test_max_workers_negative(self):
+        for number in (0, -1):
+            with self.assertRaisesRegexp(ValueError,
+                                         "max_workers must be greater "
+                                         "than 0"):
+                self.executor_type(max_workers=number)
+
 
 class ThreadPoolExecutorTest(ThreadPoolMixin, ExecutorTest, unittest.TestCase):
     def test_map_submits_without_iteration(self):
-- 
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