Backport ThreadPoolExecutor thread name from upstream

Changes from python/cpython#2315

Author: sseg

concurrent/futures/thread.py

@@ -5,6 +5,7 @@
 
 import atexit
 from concurrent.futures import _base
+import itertools
 import Queue as queue
 import threading
 import weakref
@@ -90,6 +91,10 @@ def _worker(executor_reference, work_queue):
 
 
 class ThreadPoolExecutor(_base.Executor):
+
+    # Used to assign unique thread names when thread_name_prefix is not supplied.
+    _counter = itertools.count().next
+
     def __init__(self, max_workers=None, thread_name_prefix=''):
         """Initializes a new ThreadPoolExecutor instance.
 
@@ -110,7 +115,8 @@ def __init__(self, max_workers=None, thread_name_prefix=''):
         self._threads = set()
         self._shutdown = False
         self._shutdown_lock = threading.Lock()
-        self._thread_name_prefix = thread_name_prefix
+        self._thread_name_prefix = (thread_name_prefix or
+                                    ("ThreadPoolExecutor-%d" % self._counter()))
 
     def submit(self, fn, *args, **kwargs):
         with self._shutdown_lock:

test_futures.py

@@ -248,10 +248,9 @@ def test_thread_names_default(self):
         del executor
 
         for t in threads:
-            # We don't particularly care what the default name is, just that
-            # it has a default name implying that it is a ThreadPoolExecutor
-            # followed by what looks like a thread number.
-            self.assertRegexpMatches(t.name, r'^.*ThreadPoolExecutor.*_[0-4]$')
+            # Ensure that our default name is reasonably sane and unique when
+            # no thread_name_prefix was supplied.
+            self.assertRegex(t.name, r'ThreadPoolExecutor-\d+_[0-4]$')
             t.join()