devices: wait until reader thread fully starts

On slow or highly loaded systems, the Reader thread may not be ready
by the time the _send_packet method is called, resulting in a XBeeException
("Packetlistener is not running").

In order to prevent this, block in the device open() method until the reader
thread is fully started.

This is reproducible in the IX14 XBee prototypes when they are under heavy
load (for example soon after boot).

Signed-off-by: Jose Diaz de Grenu <Jose.DiazdeGrenu@digi.com>

Author: jdepedro-digi

digi/xbee/devices.py

@@ -2021,6 +2021,7 @@ def open(self, force_settings=False):
         self._packet_listener.add_micropython_data_received_callback(mp_data_cbs)
 
         self._packet_listener.start()
+        self._packet_listener.wait_until_started()
 
         if force_settings:
             try:

digi/xbee/reader.py

@@ -14,6 +14,7 @@
 
 from concurrent.futures import ThreadPoolExecutor
 from queue import Queue, Empty
+from threading import Event
 import logging
 import threading
 import time
@@ -410,13 +411,25 @@ def __init__(self, comm_iface, xbee_device, queue_max_size=None):
         self.__xbee_device = xbee_device
         self.__comm_iface = comm_iface
         self.__stop = True
+        self.__started = Event()
 
         self.__queue_max_size = queue_max_size if queue_max_size is not None else self.__DEFAULT_QUEUE_MAX_SIZE
         self.__xbee_queue = XBeeQueue(self.__queue_max_size)
         self.__data_xbee_queue = XBeeQueue(self.__queue_max_size)
         self.__explicit_xbee_queue = XBeeQueue(self.__queue_max_size)
         self.__ip_xbee_queue = XBeeQueue(self.__queue_max_size)
 
+    def wait_until_started(self, timeout=None):
+        """
+        Blocks until the thread has fully started. If already started, returns
+        immediately.
+
+        Args:
+            timeout (Float): timeout for the operation in seconds.
+        """
+
+        self.__started.wait(timeout)
+
     def run(self):
         """
         This is the method that will be executing for listening packets.
@@ -425,6 +438,7 @@ def run(self):
         """
         try:
             self.__stop = False
+            self.__started.set()
             while not self.__stop:
                 # Try to read a packet. Read packet is unescaped.
                 raw_packet = self.__comm_iface.wait_for_frame(self.__xbee_device.operating_mode)