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docs/eCookbook/demo-programs/multi-threaded-work.md

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+**Multi-Threaded Work - Running long tasks inside of a GUI**
+
+This program demonstrates one way of using a combination of Python's Thread
+and Queue objects to implement a GUI that performs work that takes too long
+to directly perform inside of the event loop.
+
+An example use would be if you have a button that you want to use to start
+some code that will take several seconds to run, then this technique is a
+good pattern to use.
+
+Take a moment to examine the code dealing with the Thread and the Queue.  These
+constructs are nothing to fear as the amount of code that uses them is only a 
+handul of lines of code are needed.  And they are simple enough that you'll
+be able to understand them.
+
+***"Thread-safe"*** - This is an important term to consider any time you are using threads in your program.  There are 2 things to check out:
+1. You must make sure that the calls you make from your thread are OK to call from a thread
+2. If you are running multiple threads, then the calls you make must be "thread-safe"
+
+The authors of libraries you are using often tell you if their code is "thread-safe".  
+
+PySimpleGUI code is not thread safe.  For the tkinter version (i.e. plain PySimpleGUI versus PySimpleGUIQt), you cannot run PySimpleGUI as a thread.  To put that in simpler terms, you cannot make any calls into the PySimpleGUI package from a thread.  For example, you cannot call `update` for any of your elements from a thread.  This is why you see the updates happening from the main thread only.
+
+Screenshot:
+
+![SNAG-0491.jpg](/api/files/5da0877e2299175412c57964/snag-0491.jpeg "SNAG-0491.jpg")
+
+
+<iframe src='https://trinket.io/embed/pygame/8f2aeea67b?start=result' width='100%' height='650' frameborder='0' marginwidth='0' marginheight='0' allowfullscreen></iframe>