PWMProbes: Add HeartbeatThread as a child of TimerThread

IBM#38
Signed-off-by: Gabe Goodhart <ghart@us.ibm.com>

oper8/watch_manager/python_watch_manager/threads/__init__.py

@@ -1,6 +1,7 @@
 """Import the ThreadBase and subclasses"""
 # Local
 from .base import ThreadBase
+from .heartbeat import HeartbeatThread
 from .reconcile import ReconcileThread
 from .timer import TimerThread
 from .watch import WatchThread

oper8/watch_manager/python_watch_manager/threads/heartbeat.py

@@ -0,0 +1,52 @@
+"""
+Thread class that will dump a heartbeat to a file periodically
+"""
+
+# Standard
+from datetime import datetime, timedelta
+
+# Local
+from ....exceptions import assert_config
+from ..utils import parse_time_delta
+from .timer import TimerThread
+
+
+class HeartbeatThread(TimerThread):
+    """The HeartbeatThread acts as a pulse for the PythonWatchManager.
+
+    This thread will periodically dump the value of "now" to a file which can be
+    read by an observer such as a liveness/readiness probe to ensure that the
+    manager is functioning well.
+    """
+
+    # This format is designed to be read using `date -d $(cat heartbeat.txt)`
+    # using the GNU date utility
+    # CITE: https://www.gnu.org/software/coreutils/manual/html_node/Examples-of-date.html
+    _DATE_FORMAT = "%Y-%m-%d %H:%M:%S"
+
+    def __init__(self, heartbeat_file: str, heartbeat_period: str):
+        """Initialize with the file location for the heartbeat output
+
+        Args:
+            heartbeat_file: str
+                The fully-qualified path to the heartbeat file
+            heartbeat_period: str
+                Time delta string representing period delay between beats.
+                NOTE: The GNU `date` utility cannot parse sub-seconds easily, so
+                    the expected configuration for this is to be >= 1s
+        """
+        self._heartbeat_file = heartbeat_file
+        self._offset = parse_time_delta(heartbeat_period)
+        assert_config(
+            self._offset >= timedelta(seconds=1),
+            "heartbeat_period must be >= 1s",
+        )
+        super().__init__(name="heartbeat_thread")
+        self.put_event(datetime.now(), self._run_heartbeat)
+
+    def _run_heartbeat(self):
+        """Run the heartbeat dump to the heartbeat file and put the next beat"""
+        now = datetime.now()
+        with open(self._heartbeat_file, "w") as handle:
+            handle.write(now.strftime(self._DATE_FORMAT))
+        self.put_event(now + self._offset, self._run_heartbeat)

oper8/watch_manager/python_watch_manager/threads/timer.py

@@ -24,9 +24,9 @@ class TimerThread(ThreadBase, metaclass=Singleton):
     to threading.Timer stdlib class except that it uses one shared thread for all events
     instead of a thread per event."""
 
-    def __init__(self):
+    def __init__(self, name: Optional[str] = None):
         """Initialize a priorityqueue like object and a synchronization object"""
-        super().__init__(name="timer_thread", daemon=True)
+        super().__init__(name=name or "timer_thread", daemon=True)
 
         # Use a heap queue instead of a queue.PriorityQueue as we're already handling
         # synchronization with the notify condition