From c30bf9f61ee0ea67269121d99c5de48261232167 Mon Sep 17 00:00:00 2001
From: Mathew Sutcliffe <oktal3700@gmail.com>
Date: Thu, 16 Oct 2014 16:36:53 +0100
Subject: [PATCH] refs #336 Fixed CLogHandler thread safety in swiftcore.

---
 src/blackmisc/loghandler.cpp |  5 +----
 src/blackmisc/loghandler.h   | 10 ++++------
 src/blackmisc/worker.h       | 21 +++++++++++++++++++++
 src/swiftcore/tool.cpp       | 10 +++++++---
 4 files changed, 33 insertions(+), 13 deletions(-)

diff --git a/src/blackmisc/loghandler.cpp b/src/blackmisc/loghandler.cpp
index 56e4e7612..a764e5f9c 100644
--- a/src/blackmisc/loghandler.cpp
+++ b/src/blackmisc/loghandler.cpp
@@ -40,10 +40,7 @@ namespace BlackMisc
 
     CLogHandler::~CLogHandler()
     {
-        if (m_oldHandler)
-        {
-            qInstallMessageHandler(m_oldHandler);
-        }
+        qInstallMessageHandler(m_oldHandler);
     }
 
     CLogCategoryHandler *CLogHandler::handlerForCategoryPrefix(const QString &category)
diff --git a/src/blackmisc/loghandler.h b/src/blackmisc/loghandler.h
index f0645ddc4..a7537c452 100644
--- a/src/blackmisc/loghandler.h
+++ b/src/blackmisc/loghandler.h
@@ -45,10 +45,6 @@ namespace BlackMisc
         //! \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:
         //! Emitted when a message is logged in this process.
         void localMessageLogged(const BlackMisc::CStatusMessage &message);
@@ -63,6 +59,9 @@ namespace BlackMisc
         //! Called by the context to relay a message.
         void logRemoteMessage(const BlackMisc::CStatusMessage &message);
 
+        //! Enable or disable the default Qt handler.
+        void enableConsoleOutput(bool enable);
+
     private:
         void logMessage(const BlackMisc::CStatusMessage &message);
         QtMessageHandler m_oldHandler = nullptr;
@@ -80,11 +79,10 @@ namespace BlackMisc
     {
         Q_OBJECT
 
-    public:
+    public slots:
         /*!
          * 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) { Q_ASSERT(thread() == QThread::currentThread()); m_enableFallThrough = enable; }
 
diff --git a/src/blackmisc/worker.h b/src/blackmisc/worker.h
index 9f4bf5417..ee1b92931 100644
--- a/src/blackmisc/worker.h
+++ b/src/blackmisc/worker.h
@@ -14,12 +14,33 @@
 
 #include <QThread>
 #include <QMutex>
+#include <QTimer>
 #include <functional>
 #include <atomic>
 
 namespace BlackMisc
 {
 
+    /*!
+     * Starts a single-shot timer which will run in an existing thread and call a task when it times out.
+     *
+     * Useful when a worker thread wants to push small sub-tasks back to the thread which spawned it.
+     * \see QTimer::singleShot()
+     */
+    template <typename F>
+    void singleShot(int msec, QThread *target, F task)
+    {
+        auto *timer = new QTimer;
+        timer->setSingleShot(true);
+        timer->moveToThread(target);
+        QObject::connect(timer, &QTimer::timeout, [ = ]()
+        {
+            task();
+            timer->deleteLater();
+        });
+        QMetaObject::invokeMethod(timer, "start", Q_ARG(int, msec));
+    }
+
     /*!
      * Just a subclass of QThread whose destructor waits for the thread to finish.
      */
diff --git a/src/swiftcore/tool.cpp b/src/swiftcore/tool.cpp
index a8c00a1f2..5413009bb 100644
--- a/src/swiftcore/tool.cpp
+++ b/src/swiftcore/tool.cpp
@@ -4,6 +4,7 @@
 #include "blackmisc/avallclasses.h"
 #include "blackmisc/pqallquantities.h"
 #include "blackmisc/loghandler.h"
+#include "blackmisc/worker.h"
 #include "blacksound/soundgenerator.h"
 
 #include <QTextStream>
@@ -37,7 +38,7 @@ namespace BlackMiscTest
      */
     void Tool::serverLoop(BlackCore::CRuntime *runtime)
     {
-        CLogHandler::instance()->enableConsoleOutput(false);
+        QMetaObject::invokeMethod(CLogHandler::instance(), "enableConsoleOutput", Q_ARG(bool, false));
 
         Q_ASSERT(runtime);
         QThread::sleep(3); // let the DBus server startup
@@ -164,7 +165,7 @@ namespace BlackMiscTest
                 bool enable = line.endsWith("e");
                 if (line.startsWith("all"))
                 {
-                    BlackMisc::CLogHandler::instance()->enableConsoleOutput(enable);
+                    QMetaObject::invokeMethod(CLogHandler::instance(), "enableConsoleOutput", Q_ARG(bool, enable));
                 }
                 else
                 {
@@ -177,7 +178,10 @@ namespace BlackMiscTest
                     else if (line.startsWith("sim")) category = CLogCategoryList(simulatorContext).back().toQString();
                     if (! category.isEmpty())
                     {
-                        BlackMisc::CLogHandler::instance()->handlerForCategoryPrefix(category)->enableConsoleOutput(enable);
+                        BlackMisc::singleShot(0, BlackMisc::CLogHandler::instance()->thread(), [ = ]()
+                        {
+                            BlackMisc::CLogHandler::instance()->handlerForCategoryPrefix(category)->enableConsoleOutput(enable);
+                        });
                     }
                 }
             }