Avoid start multiple log watchdog threads

It is observed that `enableWatchDog` might be called after the manager
activity is resumed without user's interaction, due to some unknown
mechanism of preference refreshing.

Author: JingMatrix

daemon/src/main/jni/logcat.cpp

@@ -113,7 +113,7 @@ class Logcat {
 
     static size_t PrintLogLine(const AndroidLogEntry &entry, FILE *out);
 
-    void EnsureLogWatchDog();
+    void StartLogWatchDog();
 
     JNIEnv *env_;
     jobject thiz_;
@@ -243,9 +243,9 @@ void Logcat::ProcessBuffer(struct log_msg *buf) {
         } else if (msg == "!!refresh_verbose!!"sv) {
             RefreshFd(true);
         } else if (msg == "!!start_watchdog!!"sv) {
+            if (!enable_watchdog) StartLogWatchDog();
             enable_watchdog = true;
             enable_watchdog.notify_one();
-            EnsureLogWatchDog();
         } else if (msg == "!!stop_watchdog!!"sv) {
             enable_watchdog = false;
             enable_watchdog.notify_one();
@@ -260,20 +260,21 @@ void Logcat::ProcessBuffer(struct log_msg *buf) {
     }
 }
 
-void Logcat::EnsureLogWatchDog() {
+void Logcat::StartLogWatchDog() {
     constexpr static auto kLogdSizeProp = "persist.logd.size"sv;
     constexpr static auto kLogdTagProp = "persist.log.tag"sv;
     constexpr static auto kLogdMainSizeProp = "persist.logd.size.main"sv;
     constexpr static auto kLogdCrashSizeProp = "persist.logd.size.crash"sv;
     constexpr static long kErr = -1;
     std::thread watchdog([this] {
+        Log("[LogWatchDog started]\n");
         while (true) {
             enable_watchdog.wait(false);  // Blocking current thread until enable_watchdog is true;
             auto logd_size = GetByteProp(kLogdSizeProp);
             auto logd_tag = GetStrProp(kLogdTagProp);
             auto logd_main_size = GetByteProp(kLogdMainSizeProp);
             auto logd_crash_size = GetByteProp(kLogdCrashSizeProp);
-            Log("[LogWatchDog started] log.tag: " + logd_tag +
+            Log("[LogWatchDog running] log.tag: " + logd_tag +
                 "; logd.[default, main, crash].size: [" + std::to_string(logd_size) + "," +
                 std::to_string(logd_main_size) + "," + std::to_string(logd_crash_size) + "]\n");
             if (!logd_tag.empty() ||