From 8fff2242ff53735255247a1b126727e374fe9159 Mon Sep 17 00:00:00 2001
From: Chenjun Shen <chenjun.shen@gmail.com>
Date: Tue, 19 Dec 2017 15:19:56 +0100
Subject: [PATCH] Improve get optimal count of max_worker for pool

In the upstream of futures library, the DEFAULT value max_worker
for ThreadPoolExecutor and ProcessPoolExecutor has been changed to:

ThreadPoolExecutor

max_worker = cpu_count() * 5

Reference:
https://github.com/agronholm/pythonfutures/blob/master/concurrent/futures/thread.py#L109

ProcessPoolExecutor

max_worker = cpu_count()

Reference:
https://github.com/agronholm/pythonfutures/blob/master/concurrent/futures/process.py#L278

So we should do it as well.

Change-Id: Id68e38a639c41426f125180ad335fb1fb97cba59
Closes-bug: #1739034
---
 futurist/_futures.py                              |  2 +-
 futurist/_utils.py                                | 15 ++++++++++-----
 ...-of-max_workers-for-pool-89368859d3b819e0.yaml |  8 ++++++++
 3 files changed, 19 insertions(+), 6 deletions(-)
 create mode 100644 releasenotes/notes/improve-get-optimal-count-of-max_workers-for-pool-89368859d3b819e0.yaml

diff --git a/futurist/_futures.py b/futurist/_futures.py
index 2de69e1..4181f6d 100644
--- a/futurist/_futures.py
+++ b/futurist/_futures.py
@@ -201,7 +201,7 @@ class ProcessPoolExecutor(_process.ProcessPoolExecutor):
 
     def __init__(self, max_workers=None):
         if max_workers is None:
-            max_workers = _utils.get_optimal_thread_count()
+            max_workers = _utils.get_optimal_process_count()
         super(ProcessPoolExecutor, self).__init__(max_workers=max_workers)
         if self._max_workers <= 0:
             raise ValueError("Max workers must be greater than zero")
diff --git a/futurist/_utils.py b/futurist/_utils.py
index bb30bd3..b200d90 100644
--- a/futurist/_utils.py
+++ b/futurist/_utils.py
@@ -128,14 +128,19 @@ def get_callback_name(cb):
         return ".".join(segments)
 
 
-def get_optimal_thread_count(default=2):
+def get_optimal_thread_count(default=5):
     """Try to guess optimal thread count for current system."""
     try:
-        return multiprocessing.cpu_count() + 1
+        return multiprocessing.cpu_count() * 5
+    except NotImplementedError:
+        return default
+
+
+def get_optimal_process_count(default=1):
+    """Try to guess optimal process count for current system."""
+    try:
+        return multiprocessing.cpu_count()
     except NotImplementedError:
-        # NOTE(harlowja): apparently may raise so in this case we will
-        # just setup two threads since it's hard to know what else we
-        # should do in this situation.
         return default
 
 
diff --git a/releasenotes/notes/improve-get-optimal-count-of-max_workers-for-pool-89368859d3b819e0.yaml b/releasenotes/notes/improve-get-optimal-count-of-max_workers-for-pool-89368859d3b819e0.yaml
new file mode 100644
index 0000000..c40799f
--- /dev/null
+++ b/releasenotes/notes/improve-get-optimal-count-of-max_workers-for-pool-89368859d3b819e0.yaml
@@ -0,0 +1,8 @@
+---
+features:
+  - Improve get_optimal_thread_count() function for
+    choosing a new default value which is 5 * cpu_count()
+    for max_workers used by ThreadPoolExecutor.
+  - Add a new get_optimal_process_count() function
+    for choosing default value which is same as
+    cpu_count() used by ProcessPoolExecutor.