From 09685e8b37519820cc9750ea5c2eca3e1d03a4f6 Mon Sep 17 00:00:00 2001
From: Mathew Sutcliffe <oktal3700@gmail.com>
Date: Sun, 12 Oct 2014 20:25:35 +0100
Subject: [PATCH] refs #336 Delete CLogCategoryHandler when it is no longer
 used, and thread safety.

---
 src/blackmisc/loghandler.cpp | 10 ++++++++++
 src/blackmisc/loghandler.h   | 22 +++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/blackmisc/loghandler.cpp b/src/blackmisc/loghandler.cpp
index bfb36eb7c..7b7887200 100644
--- a/src/blackmisc/loghandler.cpp
+++ b/src/blackmisc/loghandler.cpp
@@ -48,9 +48,17 @@ namespace BlackMisc
 
     CLogCategoryHandler *CLogHandler::handlerForCategoryPrefix(const QString &category)
     {
+        Q_ASSERT(thread() == QThread::currentThread());
+
         if (! m_categoryPrefixHandlers.contains(category))
         {
             m_categoryPrefixHandlers[category] = new CLogCategoryHandler(this, m_enableFallThrough);
+
+            connect(m_categoryPrefixHandlers[category], &CLogCategoryHandler::ps_canBeDeleted, [this](CLogCategoryHandler *handler)
+            {
+                m_categoryPrefixHandlers.remove(m_categoryPrefixHandlers.key(handler));
+                QMetaObject::invokeMethod(handler, "deleteLater");
+            });
         }
 
         return m_categoryPrefixHandlers[category];
@@ -71,6 +79,8 @@ namespace BlackMisc
 
     void CLogHandler::enableConsoleOutput(bool enable)
     {
+        Q_ASSERT(thread() == QThread::currentThread());
+
         m_enableFallThrough = enable;
         for (auto *handler : m_categoryPrefixHandlers.values())
         {
diff --git a/src/blackmisc/loghandler.h b/src/blackmisc/loghandler.h
index ecb4c15d6..8c335de13 100644
--- a/src/blackmisc/loghandler.h
+++ b/src/blackmisc/loghandler.h
@@ -42,9 +42,11 @@ namespace BlackMisc
         void install();
 
         //! Return a category handler for subscribing to all messages with a category starting with the given prefix.
+        //! \warning This must only be called from the main thread.
         CLogCategoryHandler *handlerForCategoryPrefix(const QString &prefix);
 
         //! Enable or disable the default Qt handler.
+        //! \warning This must only be called from the main thread.
         void enableConsoleOutput(bool enable);
 
     signals:
@@ -82,15 +84,33 @@ namespace BlackMisc
         /*!
          * Enable or disable the default Qt handler for messages in relevant categories.
          * This can override the setting of the parent CLogHandler.
+         * \warning This must only be called from the main thread.
          */
-        void enableConsoleOutput(bool enable) { m_enableFallThrough = enable; }
+        void enableConsoleOutput(bool enable) { Q_ASSERT(thread() == QThread::currentThread()); m_enableFallThrough = enable; }
 
     signals:
         /*!
          * Emitted when a message is logged in a relevant category.
+         *
+         * When all slots are disconnected from this signal, the CLogCategoryHandler is allowed to delete itself.
          */
         void messageLogged(const CStatusMessage &message);
 
+        /*!
+         * Emitted when there are no more slots connected to the messageLogged signal.
+         */
+        void ps_canBeDeleted(CLogCategoryHandler *handler);
+
+    protected:
+        /*!
+         * \copydoc QObject::disconnectNotify
+         */
+        virtual void disconnectNotify(const QMetaMethod &) override
+        {
+            static const QMetaMethod signal = QMetaMethod::fromSignal(&CLogCategoryHandler::messageLogged);
+            if (! isSignalConnected(signal)) { emit ps_canBeDeleted(this); }
+        }
+
     private:
         friend class CLogHandler;
         CLogCategoryHandler(QObject *parent, bool enableFallThrough) : QObject(parent), m_enableFallThrough(enableFallThrough) {}