From 04d6c407af561b5a0fc9cc24ada15677d59582db Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Agel?= <bjoern.agel@janitza.de>
Date: Tue, 21 Jan 2025 18:28:00 +0100
Subject: [PATCH] cache link status method to reduce CPU time

---
 dbus-serialbattery/utils_can.py | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/dbus-serialbattery/utils_can.py b/dbus-serialbattery/utils_can.py
index 0b2ef1e..505b98c 100644
--- a/dbus-serialbattery/utils_can.py
+++ b/dbus-serialbattery/utils_can.py
@@ -30,8 +30,9 @@ def __init__(self, channel, bustype):
         self.daemon = True
         self._running = True  # flag to control the running state
         self.can_bus = None
-        self.initial_interface_state = self.get_link_status(self.channel)
+        self.initial_interface_state = self.get_link_status
         self.can_initialised = threading.Event()
+        self._link_status_cache = {"timestamp": 0, "result": None}
 
     @classmethod
     def get_instance(cls, channel, bustype) -> "CanReceiverThread":
@@ -66,7 +67,7 @@ def run(self) -> None:
         self.can_initialised.set()
 
         while self._running:
-            link_status = self.get_link_status(self.channel)
+            link_status = self.get_link_status
             if link_status:
                 try:
                     message = self.can_bus.recv(timeout=1.0)  # wait for max 1 second to receive message
@@ -132,19 +133,27 @@ def get_message_cache(self) -> dict:
             # return a copy of the current cache
             return dict(self.message_cache)
 
-    @staticmethod
-    def get_link_status(channel: str) -> bool:
+    def get_link_status(self) -> bool:
         """
         Check if the CAN interface is up
 
         :param channel: CAN interface name
         :return: True if interface is up, False otherwise
         """
-        result = subprocess.run(["ip", "link", "show", channel], capture_output=True, text=True, check=True)
-        if "UP" in result.stdout:
-            return True
-        else:
-            return False
+
+        current_time = time.time()
+        # Check if cached result is still valid
+        if self._link_status_cache["timestamp"] + 1 > current_time:
+            return self._link_status_cache["result"]
+
+        result = subprocess.run(["ip", "link", "show", self.channel], capture_output=True, text=True, check=True)
+        status = "UP" in result.stdout
+
+        # Update the cache
+        self._link_status_cache["timestamp"] = current_time
+        self._link_status_cache["result"] = status
+
+        return status
 
     @staticmethod
     def get_bitrate(channel: str) -> int: