Save session only when there is change since the last serialization

This is a slight optimization not to cause useless disk access.  This
only applies to saving session automatically (see
--save-session-interval).  aria2.saveSession and serialization at the
end of the session are always performed as before.

1 files changed, 13 insertions, 2 deletions

diff --git a/src/SaveSessionCommand.cc b/src/SaveSessionCommand.cc
index d94815ad..7e557f27 100644
--- a/src/SaveSessionCommand.cc
+++ b/src/SaveSessionCommand.cc
@@ -60,12 +60,23 @@ void SaveSessionCommand::preProcess()
 
 void SaveSessionCommand::process()
 {
+  auto& rgman = getDownloadEngine()->getRequestGroupMan();
+
+  if(!rgman->getRequireSaveSession()) {
+    A2_LOG_INFO("No change in queues since last serialization or startup. "
+                "No serialization is necessary this time.");
+    return;
+  }
+
   const std::string& filename = getDownloadEngine()->getOption()
     ->get(PREF_SAVE_SESSION);
+
   if(!filename.empty()) {
-    SessionSerializer sessionSerializer(getDownloadEngine()->
-                                        getRequestGroupMan().get());
+    SessionSerializer sessionSerializer(rgman.get());
+
     if(sessionSerializer.save(filename)) {
+      rgman->clearRequireSaveSession();
+
       A2_LOG_NOTICE(fmt(_("Serialized session to '%s' successfully."),
                         filename.c_str()));
     } else {