Merge pull request #1408 from PySimpleGUI/Dev-latest

Lots of comments

DemoPrograms/Demo_Threaded_Work.py

@@ -2,26 +2,47 @@
 import queue
 import threading
 import time
-
 import PySimpleGUI as sg
 
-# Put your long-running code in here
+"""
+    Demo on how to add a long-running item to your PySimpleGUI Event Loop
+    If you want to do something that takes a long time, and you do it in the 
+    main event loop, you'll quickly begin to see messages from windows that your
+    program has hung, asking if you want to kill it.
+    
+    The problem is not that your problem is hung, the problem is that you are 
+    not calling Read or Refresh often enough.
+    
+    One way through this, shown here, is to put your long work into a thread that
+    is spun off, allowed to work, and then gets back to the GUI when it's done working
+    on that task.
+    
+    If you have multiple long tasks to run, then you'll want a more sophisticated
+    format to your messages going back to the GUI so you'll know which task finished
+"""
+
+
+# ---------------------------------------
+# Put your long-running code in here    #
+# ---------------------------------------
 def worker_thread(thread_name, gui_queue):
     print('Starting thread - {} '.format(thread_name))
     # this is our "long running function call"
     time.sleep(5)  # sleep for a while
+    print('Ending thread - {} '.format(thread_name))
 
     # at the end of the work, before exiting, send a message back to the GUI indicating end
+    # in this case, we're using a simple string
     gui_queue.put('{} - done'.format(thread_name))  # put a message into queue for GUI
 
 
-######   ##     ## ####
+########  ##     ## ####
 ##    ##  ##     ##  ##
 ##        ##     ##  ##
 ##   #### ##     ##  ##
 ##    ##  ##     ##  ##
 ##    ##  ##     ##  ##
-######    #######  ####
+########  ######### ####
 
 def the_gui(gui_queue):
 
@@ -32,29 +53,27 @@ def the_gui(gui_queue):
 
     window = sg.Window('Multithreaded Window').Layout(layout)
     # --------------------- EVENT LOOP ---------------------
-    message = None
     count = 0
     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
-        if event == 'Go':
+        if event == 'Go':           # clicking "Go" starts a long running work item by starting thread
             window.Element('_OUTPUT_').Update('Starting long work %s'%count)
-            # simulate STARTING long run by starting a thread
+            # STARTING long run by starting a thread
             threading.Thread(target=worker_thread, args=('Thread %s'%count, gui_queue,), daemon=True).start()
             count += 1
-        # --------------- Loop through all messages coming in from threads ---------------
+        # --------------- Read next message coming in from threads ---------------
-        try:  # see if something has been posted to Queue
+        try:
-            message = gui_queue.get_nowait()
+            message = gui_queue.get_nowait()   # see if something has been posted to Queue
-        except queue.Empty:  # get_nowait() will get exception when Queue is empty
+        except queue.Empty:             # get_nowait() will get exception when Queue is empty
-            pass             # nothing in queue so do nothing
+            message = None              # nothing in queue so do nothing
 
         # if message received from queue, display the message in the Window
         if message is not None:
             # this is the place you would execute code at ENDING of long running task
             window.Element('_OUTPUT_').Update(message)
             window.Refresh()  # do a refresh because could be showing multiple messages before next Read
-            message = None
 
     # if user exits the window, then close the window and exit the GUI func
     window.Close()