Merge pull request #1191 from PySimpleGUI/Dev-latest

Dev latest

DemoPrograms/Demo_Multithreaded_Queued.py

@@ -7,8 +7,17 @@ import PySimpleGUI as sg
 """
     DESIGN PATTERN - Multithreaded GUI
     One method for running multiple threads in a PySimpleGUI environment.
-    This design pattern works for all of the flavors of PySimpleGUI including the Web and also repl.it
+    The PySimpleGUI code, and thus the underlying GUI framework, runs as the primary, main thread
+    Other parts of the software are implemented as threads
     
+    A queue.Queue is used by the worker threads to communicate with code that calls PySimpleGUI directly.
+    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
 """
 
 
@@ -21,7 +30,7 @@ def worker_thread(thread_name, run_freq,  gui_queue):
     :param gui_queue: Queue used to communicate with the GUI
     :return:
     """
-    print('Strarting thread - ', thread_name)
+    print('Starting thread - ', thread_name)
     i = 0
     while True:
         sleep(run_freq/1000)
@@ -43,17 +52,19 @@ def the_gui(gui_queue):
     window = sg.Window('Window Title').Layout(layout)
 
     while True:             # Event Loop
-        event, values = window.Read(timeout=200)        # wait for up to 200 ms for a GUI event
+        event, values = window.Read(timeout=100)        # wait for up to 200 ms for a GUI event
         if event is None or event == 'Exit':
             break
         #--------------- Handle stuff coming in from threads ---------------
-        try:                    # see if something has been posted to Queue
+        while True:                 # loop executes until runs out of messages in Queue
-            message = gui_queue.get_nowait()
+            try:                    # see if something has been posted to Queue
-        except:
+                message = gui_queue.get_nowait()
-            message = None      # indicate nothing posted
+            except:                 # will get exception when Queue is empty
-        # if message received from queue, display the message in the Window
+                break               # break from the loop if no more messages are queued up
-        if message:
+            # if message received from queue, display the message in the Window
-            window.Element('_OUTPUT_').Update(message)
+            if message:
+                window.Element('_OUTPUT_').Update(message)
+                window.Refresh()
 
     # if user exits the window, then close the window and exit
     window.Close()
@@ -63,9 +74,7 @@ if __name__ == '__main__':
     #-- Create a Queue to communicate with GUI --
     gui_queue = Queue()             # queue used to communicate between the gui and the worker
     #-- Start worker threads, one runs twice as often as the other
-    thread = Thread(target=worker_thread, args=('Thread 1', 1000, gui_queue,),  daemon=True)
+    Thread(target=worker_thread, args=('Thread 1', 500, gui_queue,),  daemon=True).start()
-    thread.start()
+    Thread(target=worker_thread, args=('Thread 2', 200, gui_queue,),  daemon=True).start()
-    thread = Thread(target=worker_thread, args=('Thread 2', 500, gui_queue,),  daemon=True)
-    thread.start()
     #-- Start the GUI passing in the Queue --
     the_gui(gui_queue)