From 474917b50b07f2167873d244f05715e986f47659 Mon Sep 17 00:00:00 2001
From: MikeTheWatchGuy <mike_barnett@hotmail.com>
Date: Tue, 9 Jul 2019 13:09:25 -0400
Subject: [PATCH] Multithreaded for doing long tasks Demo

---
 DemoPrograms/Demo_Multithreaded_Long_Tasks.py | 106 ++++++++++++++++++
 1 file changed, 106 insertions(+)
 create mode 100644 DemoPrograms/Demo_Multithreaded_Long_Tasks.py

diff --git a/DemoPrograms/Demo_Multithreaded_Long_Tasks.py b/DemoPrograms/Demo_Multithreaded_Long_Tasks.py
new file mode 100644
index 00000000..f74bee00
--- /dev/null
+++ b/DemoPrograms/Demo_Multithreaded_Long_Tasks.py
@@ -0,0 +1,106 @@
+#!/usr/bin/python3
+
+import queue
+import threading
+import time
+
+# This program has been tested on all flavors of PySimpleGUI and it works with no problems at all
+# To try something other than tkinter version, just comment out the first import and uncomment the one you want
+import PySimpleGUI as sg
+# import PySimpleGUIQt as sg
+# import PySimpleGUIWx as sg
+# import PySimpleGUIWeb as sg
+
+"""
+    DESIGN PATTERN - Multithreaded Long Tasks GUI
+    Presents one method for running long-running operations in a PySimpleGUI environment.
+    The PySimpleGUI code, and thus the underlying GUI framework, runs as the primary, main thread
+    The "long work" is contained in the thread that is being started.
+
+    A queue.Queue is used by the threads to communicate with main GUI code
+    The PySimpleGUI code is structured just like a typical PySimpleGUI program.  A layout defined,
+        a Window is created, and an event loop is executed.
+    What's different is that within this otherwise normal PySimpleGUI Event Loop, there is a check for items
+        in the Queue.  If there are items found, process them by making GUI changes, and continue.
+
+    This design pattern works for all of the flavors of PySimpleGUI including the Web and also repl.it
+    You'll find a repl.it version here: https://repl.it/@PySimpleGUI/Async-With-Queue-Communicationspy
+"""
+
+
+def long_operation_thread(seconds, gui_queue):
+    """
+    A worker thread that communicates with the GUI through a queue
+    This thread can block for as long as it wants and the GUI will not be affected
+    :param seconds: (int) How long to sleep, the ultimate blocking call
+    :param gui_queue: (queue.Queue) Queue to communicate back to GUI that task is completed
+    :return:
+    """
+    print('Starting thread - will sleep for {} seconds'.format(seconds))
+    time.sleep(seconds)                  # sleep for a while
+    gui_queue.put('** Done **')  # put a message into queue for GUI
+
+
+######   ##     ## ####
+##    ##  ##     ##  ##
+##        ##     ##  ##
+##   #### ##     ##  ##
+##    ##  ##     ##  ##
+##    ##  ##     ##  ##
+######    #######  ####
+
+def the_gui():
+    """
+    Starts and executes the GUI
+    Reads data from a Queue and displays the data to the window
+    Returns when the user exits / closes the window
+    """
+
+    gui_queue = queue.Queue()  # queue used to communicate between the gui and the threads
+
+    layout = [[sg.Text('Long task to perform example')],
+              [sg.Output(size=(70, 12))],
+              [sg.Text('Number of seconds your task will take'),sg.Input(key='_SECONDS_', size=(5,1)), sg.Button('Do Long Task', bind_return_key=True)],
+              [sg.Button('Click Me'), sg.Button('Exit')], ]
+
+    window = sg.Window('Multithreaded Window').Layout(layout)
+
+    # --------------------- EVENT LOOP ---------------------
+    while True:
+        event, values = window.Read(timeout=100)       # wait for up to 100 ms for a GUI event
+        if event is None or event == 'Exit':
+            break
+        elif event.startswith('Do'):
+            try:
+                seconds = int(values['_SECONDS_'])
+                print('Starting thread to do long work....sending value of {} seconds'.format(seconds))
+                threading.Thread(target=long_operation_thread, args=(seconds , gui_queue,), daemon=True).start()
+            except Exception as e:
+                print('Error starting work thread. Did you input a valid # of seconds? You entered: %s' % values['_SECONDS_'])
+        elif event == 'Click Me':
+            print('Your GUI is alive and well')
+        # --------------- Check for incoming messages from threads  ---------------
+        try:
+            message = gui_queue.get_nowait()
+        except queue.Empty:             # get_nowait() will get exception when Queue is empty
+            message = None              # break from the loop if no more messages are queued up
+
+        # if message received from queue, display the message in the Window
+        if message:
+            print('Got a message back from the thread: ', message)
+
+    # if user exits the window, then close the window and exit the GUI func
+    window.Close()
+
+
+##     ##    ###    #### ##    ##
+###   ###   ## ##    ##  ###   ##
+#### ####  ##   ##   ##  ####  ##
+## ### ## ##     ##  ##  ## ## ##
+##     ## #########  ##  ##  ####
+##     ## ##     ##  ##  ##   ###
+##     ## ##     ## #### ##    ##
+
+if __name__ == '__main__':
+    the_gui()
+    print('Exiting Program')
\ No newline at end of file