From 06ad77ee9df1556b143777352a1b63fa93524901 Mon Sep 17 00:00:00 2001
From: Mathew Sutcliffe <oktal3700@gmail.com>
Date: Wed, 9 Mar 2016 20:46:39 +0000
Subject: [PATCH] refs #601 CDataCache overrides connectPage to provide a queue
 that is more flexible than the usual Qt::QueuedConnection.

---
 src/blackmisc/datacache.cpp | 37 +++++++++++++++++++++++++++++++++++++
 src/blackmisc/datacache.h   | 30 ++++++++++++++++++++++++++++++
 src/blackmisc/valuecache.h  |  3 ++-
 3 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/src/blackmisc/datacache.cpp b/src/blackmisc/datacache.cpp
index d2091fb93..ea8bd5c2a 100644
--- a/src/blackmisc/datacache.cpp
+++ b/src/blackmisc/datacache.cpp
@@ -14,11 +14,15 @@
 #include "blackmisc/identifier.h"
 #include "blackmisc/atomicfile.h"
 #include <QStandardPaths>
+#include <QTimer>
 #include <utility>
 
 namespace BlackMisc
 {
 
+    using Private::CValuePage;
+    using Private::CDataPageQueue;
+
     class CDataCacheRevision::LockGuard
     {
     public:
@@ -149,6 +153,39 @@ namespace BlackMisc
         });
     }
 
+    void CDataCache::connectPage(CValuePage *page)
+    {
+        auto *queue = new CDataPageQueue(page);
+        connect(page, &CValuePage::valuesWantToCache, this, &CDataCache::changeValues);
+        connect(this, &CDataCache::valuesChanged, queue, &CDataPageQueue::queueValuesFromCache, Qt::DirectConnection);
+
+        auto *timer = new QTimer(page);
+        connect(timer, &QTimer::timeout, queue, &CDataPageQueue::trySetQueuedValuesFromCache);
+        timer->start(0);
+    }
+
+    void CDataPageQueue::queueValuesFromCache(const CValueCachePacket &values, QObject *changedBy)
+    {
+        QMutexLocker lock(&m_mutex);
+        m_queue.push_back(std::make_pair(values, changedBy));
+    }
+
+    void CDataPageQueue::trySetQueuedValuesFromCache()
+    {
+        bool locked = m_mutex.tryLock(0);
+        if (locked)
+        {
+            decltype(m_queue) queue;
+            qSwap(m_queue, queue);
+            m_mutex.unlock();
+
+            for (const auto &pair : queue)
+            {
+                m_page->setValuesFromCache(pair.first, pair.second);
+            }
+        }
+    }
+
     CDataCacheSerializer::CDataCacheSerializer(CDataCache *owner, const QString &revisionFileName) :
         CContinuousWorker(owner),
         m_cache(owner),
diff --git a/src/blackmisc/datacache.h b/src/blackmisc/datacache.h
index 9c1304fd2..3a8a9b487 100644
--- a/src/blackmisc/datacache.h
+++ b/src/blackmisc/datacache.h
@@ -22,6 +22,34 @@
 
 namespace BlackMisc
 {
+    namespace Private
+    {
+        /*!
+         * Decorator for CValuePage which allows incoming remote changes to be queued to allow for more
+         * flexibility to control how the queue is popped compared to the usual Qt::QueuedConnection.
+         */
+        class BLACKMISC_EXPORT CDataPageQueue : public QObject
+        {
+            Q_OBJECT
+
+        public:
+            //! Constructor.
+            CDataPageQueue(CValuePage *parent) : QObject(parent), m_page(parent) {}
+
+            //! Add to the queue to synchronize with a change caused by another page.
+            //! \threadsafe
+            void queueValuesFromCache(const BlackMisc::CValueCachePacket &values, QObject *changedBy);
+
+            //! Synchronize with changes queued by queueValuesFromCache, if the mutex is not currently locked.
+            void trySetQueuedValuesFromCache();
+
+        private:
+            CValuePage *m_page = nullptr;
+            QList<std::pair<CValueCachePacket, QObject*>> m_queue;
+            QMutex m_mutex;
+        };
+    }
+
     class CDataCache;
 
     /*!
@@ -169,6 +197,8 @@ namespace BlackMisc
         void saveToStoreAsync(const BlackMisc::CValueCachePacket &values);
         void loadFromStoreAsync();
 
+        virtual void connectPage(Private::CValuePage *page) override;
+
         QFileSystemWatcher m_watcher;
         const QString m_revisionFileName { persistentStore() + "/.rev" };
 
diff --git a/src/blackmisc/valuecache.h b/src/blackmisc/valuecache.h
index 2645ec43c..98abee759 100644
--- a/src/blackmisc/valuecache.h
+++ b/src/blackmisc/valuecache.h
@@ -246,7 +246,8 @@ namespace BlackMisc
         //! \private
         void valuesChanged(const BlackMisc::CValueCachePacket &values, QObject *changedBy);
 
-    private slots:
+    protected slots:
+        //! \private
         void changeValues(const BlackMisc::CValueCachePacket &values);
     };