Docs: add an example using the multiprocessing module

Author: BoboTiG

CHANGELOG

@@ -5,10 +5,11 @@ History:
 5.0.0   2019/xx/xx
       - removed support for Python 2.7
       - MSS: improve type annotations and add CI check
+      - doc: add an example using the multiprocessing module (closes #82)
 
 4.0.2   2019/02/23
       - new contributor: foone
-      - Windows: ignore missing SetProcessDPIAware() on Window XP
+      - Windows: ignore missing SetProcessDPIAware() on Window XP (fixes #109)
 
 4.0.1   2019/01/26
       - Linux: fix several XLib functions signature (fixes #92)

docs/source/examples.rst

@@ -129,10 +129,21 @@ Benchmark
 Simple naive benchmark to compare with `Reading game frames in Python with OpenCV - Python Plays GTA V <https://pythonprogramming.net/game-frames-open-cv-python-plays-gta-v/>`_:
 
 .. literalinclude:: examples/fps.py
-    :lines: 12-
+    :lines: 9-
 
 .. versionadded:: 3.0.0
 
+Multiprocessing
+---------------
+
+Performances can be improved by delegating the PNG file creation to a specific worker.
+This is a simple example using the :py:mod:`multiprocessing` inspired by the `TensorFlow Object Detection Introduction <https://github.com/pythonlessons/TensorFlow-object-detection-tutorial>`_ project:
+
+.. literalinclude:: examples/fps_multiprocessing.py
+    :lines: 9-
+
+.. versionadded:: 5.0.0
+
 
 BGRA to RGB
 ===========

docs/source/examples/fps_multiprocessing.py

@@ -0,0 +1,50 @@
+"""
+This is part of the MSS Python's module.
+Source: https://github.com/BoboTiG/python-mss
+
+Example using the multiprocessing module to speed-up screen capture.
+    https://github.com/pythonlessons/TensorFlow-object-detection-tutorial
+"""
+
+from multiprocessing import Process, Queue
+
+import mss
+import mss.tools
+
+
+def grab(queue):
+    # type: (Queue) -> None
+
+    rect = {"top": 0, "left": 0, "width": 600, "height": 800}
+
+    with mss.mss() as sct:
+        for _ in range(1_000):
+            queue.put(sct.grab(rect))
+
+    # Tell the other worker to stop
+    queue.put(None)
+
+
+def save(queue):
+    # type: (Queue) -> None
+
+    number = 0
+    output = "screenshots/file_{}.png"
+    to_png = mss.tools.to_png
+
+    while "there are screenshots":
+        img = queue.get()
+        if img is None:
+            break
+
+        to_png(img.rgb, img.size, output=output.format(number))
+        number += 1
+
+
+if __name__ == "__main__":
+    # The screenshots queue
+    queue = Queue()  # type: Queue
+
+    # 2 processes: one for grabing and one for saving PNG files
+    Process(target=grab, args=(queue,)).start()
+    Process(target=save, args=(queue,)).start()