From 5111f73da157233df0c8ed17ec89b666aef8f30f Mon Sep 17 00:00:00 2001
From: Wiebe Cazemier <wiebe@halfgaar.net>
Date: Mon, 6 Sep 2021 21:51:41 +0200
Subject: [PATCH] Reduce blocking of threads when saving state

---
 mainapp.cpp           | 30 +++++++++++++++++++++++++++++-
 mainapp.h             |  4 ++++
 subscriptionstore.cpp |  2 +-
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/mainapp.cpp b/mainapp.cpp
index 19c8b52..197f3dc 100644
--- a/mainapp.cpp
+++ b/mainapp.cpp
@@ -210,7 +210,7 @@ MainApp::MainApp(const std::string &configFilePath) :
         subscriptionStore->loadSessionsAndSubscriptions(settings->getSessionsDBFile());
     }
 
-    auto fSaveState = std::bind(&MainApp::saveState, this);
+    auto fSaveState = std::bind(&MainApp::saveStateInThread, this);
     timer.addCallback(fSaveState, 900000, "Save state.");
 }
 
@@ -355,8 +355,31 @@ void MainApp::queuePublishStatsOnDollarTopic()
     }
 }
 
+/**
+ * @brief MainApp::saveStateInThread starts a thread for disk IO, because file IO is not async.
+ */
+void MainApp::saveStateInThread()
+{
+    // Prevent queueing it again when it's still running.
+    std::unique_lock<std::mutex> locker(saveStateMutex, std::try_to_lock);
+    if (!locker.owns_lock())
+        return;
+
+    // Join previous instances.
+    if (saveStateThread.joinable())
+        saveStateThread.join();
+
+    auto f = std::bind(&MainApp::saveState, this);
+    saveStateThread = std::thread(f);
+
+    pthread_t native = saveStateThread.native_handle();
+    pthread_setname_np(native, "SaveState");
+}
+
 void MainApp::saveState()
 {
+    std::lock_guard<std::mutex> lg(saveStateMutex);
+
     try
     {
         if (!settings->storageDir.empty())
@@ -366,6 +389,8 @@ void MainApp::saveState()
 
             const std::string sessionsDBPath = settings->getSessionsDBFile();
             subscriptionStore->saveSessionsAndSubscriptions(sessionsDBPath);
+
+            logger->logf(LOG_INFO, "Saving states done");
         }
     }
     catch(std::exception &ex)
@@ -669,6 +694,9 @@ void MainApp::start()
     }
 
     saveState();
+
+    if (saveStateThread.joinable())
+        saveStateThread.join();
 }
 
 void MainApp::quit()
diff --git a/mainapp.h b/mainapp.h
index 1cb053c..1bd3406 100644
--- a/mainapp.h
+++ b/mainapp.h
@@ -71,6 +71,9 @@ class MainApp
 
     Logger *logger = Logger::getInstance();
 
+    std::thread saveStateThread;
+    std::mutex saveStateMutex;
+
     void setlimits();
     void loadConfig();
     void reloadConfig();
@@ -84,6 +87,7 @@ class MainApp
     void setFuzzFile(const std::string &fuzzFilePath);
     void queuePublishStatsOnDollarTopic();
     void saveState();
+    void saveStateInThread();
 
     MainApp(const std::string &configFilePath);
 public:
diff --git a/subscriptionstore.cpp b/subscriptionstore.cpp
index 6f62d4b..0fbbde5 100644
--- a/subscriptionstore.cpp
+++ b/subscriptionstore.cpp
@@ -634,7 +634,7 @@ void SubscriptionStore::saveSessionsAndSubscriptions(const std::string &filePath
     logger->logf(LOG_INFO, "Saving sessions and subscriptions to '%s'", filePath.c_str());
 
     RWLockGuard lock_guard(&subscriptionsRwlock);
-    lock_guard.wrlock();
+    lock_guard.rdlock();
 
     // First copy the sessions...
 
--
libgit2 0.21.4