New Demo - indirectly call sg.popup from a thread

DemoPrograms/Demo_Multithreaded_popup.py

@@ -0,0 +1,83 @@
+import threading
+import time
+import PySimpleGUI as sg
+import queue
+
+"""
+    Threading Demo - "Call popup from a thread"
+
+    Can be extended to call any PySimpleGUI function by passing the function through the queue
+
+
+    Safest approach to threading is to use a Queue object to communicate
+    between threads and maintrhead.
+
+    The thread calls popup, a LOCAL function that should be called with the same
+    parameters that would be used to call opiup when called directly
+
+    The parameters passed to the local popup are passed through a queue to the main thread.
+    When a messages is received from the queue, sg.popup is called using the parms passed
+    through the queue
+    
+    Copyright 2021 PySimpleGUI.org
+"""
+
+mainthread_queue:queue.Queue = None
+
+def popup(*args, **kwargs):
+    if mainthread_queue:
+        mainthread_queue.put((args, kwargs))
+
+def the_thread():
+    """
+    The thread that communicates with the application through the window's events.
+
+    Once a second wakes and sends a new event and associated value to the window
+    """
+    i = 0
+    while True:
+        time.sleep(2)
+        popup('Hello, this is the thread', 'My counter value', i, text_color='white', background_color='red', non_blocking=True)
+        i += 1
+
+
+def process_popup():
+    try:
+        queued_value = mainthread_queue.get_nowait()
+        sg.popup_auto_close(*queued_value[0], **queued_value[1])
+    except queue.Empty:     # get_nowait() will get exception when Queue is empty
+        pass
+
+
+def main():
+    """
+    The demo will display in the multiline info about the event and values dictionary as it is being
+    returned from window.read()
+    Every time "Start" is clicked a new thread is started
+    Try clicking "Dummy" to see that the window is active while the thread stuff is happening in the background
+    """
+    global mainthread_queue
+
+    mainthread_queue = queue.Queue()
+
+    layout = [  [sg.Text('Output Area - cprint\'s route to here', font='Any 15')],
+                [sg.Multiline(size=(65,20), key='-ML-', autoscroll=True, reroute_stdout=True, write_only=True, reroute_cprint=True)],
+                [sg.T('Input so you can see data in your dictionary')],
+                [sg.Input(key='-IN-', size=(30,1))],
+                [sg.B('Start A Thread'), sg.B('Dummy'), sg.Button('Exit')]  ]
+
+    window = sg.Window('Window Title', layout, finalize=True)
+
+    while True:             # Event Loop
+        event, values = window.read(timeout=500)
+        sg.cprint(event, values) if event != sg.TIMEOUT_EVENT else None
+        if event == sg.WIN_CLOSED or event == 'Exit':
+            break
+        process_popup()
+        if event.startswith('Start'):
+            threading.Thread(target=the_thread, daemon=True).start()
+    window.close()
+
+
+if __name__ == '__main__':
+    main()