StateFile: schedule timer only after a change

Save the state file 2 minutes after the last change.  This reduces the
disruptions by an idle MPD, and MPD can be paged out permanently until
it is used.

NEWS

@@ -13,7 +13,7 @@ ver 0.18 (2012/??/??)
   - new option "tags" may be used to disable sending tags to output
   - alsa: workaround for noise after manual song change
 * improved decoder/output error reporting
-
+* eliminate timer wakeup on idle MPD
 
 ver 0.17.4 (2013/??/??)
 * protocol:

src/Main.cxx

@@ -347,6 +347,9 @@ idle_event_emitted(void)
 	unsigned flags = idle_get();
 	if (flags != 0)
 		client_list->IdleAdd(flags);
+
+	if (flags & (IDLE_PLAYLIST|IDLE_PLAYER|IDLE_MIXER|IDLE_OUTPUT))
+		state_file->CheckModified();
 }
 
 /**

src/StateFile.cxx

@@ -41,7 +41,6 @@ StateFile::StateFile(Path &&_path, const char *_path_utf8,
 	 prev_volume_version(0), prev_output_version(0),
 	 prev_playlist_version(0)
 {
-	ScheduleSeconds(5 * 60);
 }
 
 void
@@ -110,24 +109,16 @@ StateFile::Read()
 	RememberVersions();
 }
 
-inline void
-StateFile::AutoWrite()
+void
+StateFile::CheckModified()
 {
-	if (!IsModified())
-		/* nothing has changed - don't save the state file,
-		   don't spin up the hard disk */
-		return;
-
-	Write();
+	if (!IsActive() && IsModified())
+		ScheduleSeconds(2 * 60);
 }
 
-/**
- * This function is called every 5 minutes by the GLib main loop, and
- * saves the state file.
- */
 bool
 StateFile::OnTimeout()
 {
-	AutoWrite();
-	return true;
+	Write();
+	return false;
 }

src/StateFile.hxx

@@ -48,6 +48,11 @@ public:
 	void Read();
 	void Write();
 
+	/**
+	 * Schedules a write if MPD's state was modified.
+	 */
+	void CheckModified();
+
 private:
 	/**
 	 * Save the current state versions for use with IsModified().
@@ -61,8 +66,6 @@ private:
 	gcc_pure
 	bool IsModified() const;
 
-	void AutoWrite();
-
 	/* virtual methods from TimeoutMonitor */
 	virtual bool OnTimeout() override;
 };