New Demo - Multithreaded using global memory

DemoPrograms/Demo_Multithreaded_Long_Task_Simple.py

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+#!/usr/bin/python3
+import queue
+import threading
+import time
+import PySimpleGUI as sg
+
+# This program has been tested on all flavors of PySimpleGUI and it works with no problems at all
+
+"""
+    DESIGN PATTERN - Multithreaded Long Tasks GUI using shared global variables
+    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.
+
+    The PySimpleGUI code is structured just like a typical PySimpleGUI program.  A layout defined,
+        a Window is created, and an event loop is executed.
+"""
+
+
+thread_done = 1
+message = ''
+thread_counter = 0
+
+def long_operation_thread(seconds):
+    """
+    A worker thread that communicates with the GUI through a global variable
+    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
+    :return:
+    """
+
+    global thread_done, message, thread_counter
+
+    print('Starting thread - will sleep for {} seconds'.format(seconds))
+    thread_counter += 1
+    time.sleep(seconds)                  # sleep for a while
+    message = f'***This is a message from the thread {thread_counter} ***'
+    thread_done = True
+
+
+def the_gui():
+    """
+    Starts and executes the GUI
+    Reads data from a global variable and displays
+    Returns when the user exits / closes the window
+    """
+    global thread_done, message
+
+    sg.change_look_and_feel('Light Brown 3')
+
+    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)
+
+    # --------------------- EVENT LOOP ---------------------
+    while True:
+        event, values = window.read(timeout=100)
+        if event in (None, 'Exit'):
+            break
+        elif event.startswith('Do'):
+            seconds = float(values['-SECONDS-'])
+            print('Thread ALIVE! Long work....sending value of {} seconds'.format(seconds))
+            threading.Thread(target=long_operation_thread, args=(seconds, ), daemon=True).start()
+        elif event == 'Click Me':
+            print('Your GUI is alive and well')
+        # --------------- Check for incoming messages from threads  ---------------
+        if thread_done is True:
+            print('The thread has finished!')
+            print(f'message = {message}')
+            thread_done = False
+            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')