sensor: Use pipe to interrupt loop

The `time.sleep` function cannot be stopped prematurely.  This means
that when the program receives a signal indicating it should stop, it
will not be able to do so until the running `sleep` completes.  This
means it could take up to 10 seconds for the process to stop.

A better way to handle the shutdown signal is to use a pipe.  When the
signal is received, the write end of the pipe is closed.  The event loop
will detect this immediately, as `select.select` returns as soon as any
event occurs on any of the polled file descriptors, or the timeout
expires.

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "thermostat"
-version = "0.2.0"
+version = "0.3.0dev1"
 description = ""
 authors = ["Dustin C. Hatch <dustin@hatch.name>"]
 

src/thermostat/sensor.py

@@ -1,6 +1,7 @@
 import json
 import logging
 import os
+import select
 import signal
 import time
 from contextlib import closing
@@ -52,12 +53,12 @@ SENSOR_CONFIG = {
 
 class Daemon:
     def __init__(self) -> None:
-        self.running = True
+        self.quitpipe = os.pipe()
 
     def on_signal(self, signum: int, frame: FrameType) -> None:
         log.debug("Got signal %d at %s", signum, frame)
         log.info("Stopping")
-        self.running = False
+        os.close(self.quitpipe[1])
 
     def run(self):
         signal.signal(signal.SIGINT, self.on_signal)
@@ -73,7 +74,7 @@ class Daemon:
         client.loop_start()
         with closing(smbus2.SMBus(I2CPORT)) as bus:
             params = bme280.load_calibration_params(bus, SENSOR_ADDR)
-            while self.running:
+            while 1:
                 data = bme280.sample(bus, SENSOR_ADDR, params)
                 values = {
                     "temperature": int(data.temperature),
@@ -81,7 +82,10 @@ class Daemon:
                     "humidity": int(data.humidity),
                 }
                 client.publish(TOPIC, json.dumps(values))
-                time.sleep(10)
+                ready = select.select((self.quitpipe[0],), (), (), 10)[0]
+                if self.quitpipe[0] in ready:
+                    os.close(self.quitpipe[0])
+                    break
         client.disconnect()
         client.loop_stop()