Expand the R3PTAR example to show better threading practices

Author: ddemidov

demo/R3PTAR/r3ptar.py

@@ -2,23 +2,24 @@
 
 import time
 import threading
+import signal
 import ev3dev.ev3 as ev3
 
-def tail_waggler():
+def tail_waggler(done):
     """
     This is the first thread of execution that will be responsible for waggling
     r3ptar's tail every couple of seconds.
     """
     m = ev3.MediumMotor(); assert m.connected
 
-    while True:
+    while not done.is_set():
         m.run_timed(speed_sp=90, time_sp=1000, stop_action='coast')
         time.sleep(1)
         ev3.Sound.play('rattle-snake.wav').wait()
         m.run_timed(speed_sp=-90, time_sp=1000, stop_action='coast')
         time.sleep(2)
 
-def hand_biter():
+def hand_biter(done):
     """
     This is the second thread of execution. It will constantly poll the
     infrared sensor for proximity info and bite anything that gets too close.
@@ -28,9 +29,11 @@ def hand_biter():
 
     m.run_timed(speed_sp=-200, time_sp=1000, stop_action='brake')
 
-    while True:
+    while not done.is_set():
         # Wait until something (a hand?!) gets too close:
-        while s.proximity() > 30: time.sleep(0.1)
+        while s.proximity() > 30:
+            if done.is_set(): return
+            time.sleep(0.1)
 
         # Bite it! Also, don't forget to hiss:
         ev3.Sound.play('snake-hiss.wav')
@@ -39,10 +42,32 @@ def hand_biter():
         m.run_timed(speed_sp=-200, time_sp=500, stop_action='brake')
         time.sleep(1)
 
+# The 'done' event will be used to signal the threads to stop:
+done = threading.Event()
 
-# Now that we have the worker functions defined, lets start them both in
-# separate threads.
-# Actually, we could run just one of those in a separate thread, and call the
-# other from our own (master) thread, but this way seems to be more symmetric:
-threading.Thread(target=tail_waggler).start()
-threading.Thread(target=hand_biter).start()
+# We also need to catch SIGINT (keyboard interrup) and SIGTERM (termination
+# signal from brickman) and exit gracefully:
+def signal_handler(signal, frame):
+    done.set()
+
+signal.signal(signal.SIGINT,  signal_handler)
+signal.signal(signal.SIGTERM, signal_handler)
+
+# Now that we have the worker functions defined, lets run those in separate
+# threads.
+tail = threading.Thread(target=tail_waggler, args=(done,))
+head = threading.Thread(target=hand_biter,   args=(done,))
+
+tail.start()
+head.start()
+
+# The main thread will wait for the 'back' button to be pressed.  When that
+# happens, it will signal the worker threads to stop and wait for their
+# completion.
+btn = ev3.Button()
+while not btn.backspace and not done.is_set():
+    time.sleep(0.1)
+
+done.set()
+tail.join()
+head.join()