watchdog_kick: non-allocating (#22892)

* non-allocating

* unpack

* call kick every second

* cleanup include

selfdrive/common/watchdog.cc

@@ -1,19 +1,12 @@
 #include "selfdrive/common/watchdog.h"
-
-#include <unistd.h>
-
-#include <cstdint>
-#include <string>
-
 #include "selfdrive/common/timing.h"
 #include "selfdrive/common/util.h"
 
 const std::string watchdog_fn_prefix = "/dev/shm/wd_";  // + <pid>
 
 bool watchdog_kick() {
-  std::string fn = watchdog_fn_prefix + std::to_string(getpid());
-  std::string cur_t = std::to_string(nanos_since_boot());
+  static std::string fn = watchdog_fn_prefix + std::to_string(getpid());
 
-  int r = util::write_file(fn.c_str(), cur_t.data(), cur_t.length(), O_WRONLY | O_CREAT);
-  return r == 0;
+  uint64_t ts = nanos_since_boot();
+  return util::write_file(fn.c_str(), &ts, sizeof(ts), O_WRONLY | O_CREAT) > 0;
 }

selfdrive/manager/process.py

@@ -1,6 +1,7 @@
 import importlib
 import os
 import signal
+import struct
 import time
 import subprocess
 from abc import ABC, abstractmethod
@@ -88,7 +89,7 @@ class ManagerProcess(ABC):
 
     try:
       fn = WATCHDOG_FN + str(self.proc.pid)
-      self.last_watchdog_time = int(open(fn).read())
+      self.last_watchdog_time = struct.unpack('Q', open(fn, "rb").read())[0]
     except Exception:
       pass
 

selfdrive/ui/ui.cc

@@ -245,7 +245,9 @@ void QUIState::update() {
     emit offroadTransition(!ui_state.scene.started);
   }
 
-  watchdog_kick();
+  if (ui_state.sm->frame % UI_FREQ == 0) {
+    watchdog_kick();
+  }
   emit uiUpdate(ui_state);
 }