Fix a memory leak in the material shader cache.

There were multiple problems in the implementation of the shader cache:
 1) it was not thread-safe
 2) nothing was ever removed from the hash
 3) since the keys into the hash are the actual shader source code, problem
    #2 would lead to serious memory consumption over time

Change-Id: I20d1fb2074932e23f89edddba12e68ab8adcbff0
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

5 files changed, 39 insertions, 5 deletions

diff --git a/src/quick/items/qquickshadereffectnode.cpp b/src/quick/items/qquickshadereffectnode.cpp
index 3542fbb27f..e593112ef5 100644
--- a/src/quick/items/qquickshadereffectnode.cpp
+++ b/src/quick/items/qquickshadereffectnode.cpp
@@ -38,6 +38,7 @@
 #include <QtQuick/private/qsgrenderer_p.h>
 #include <QtQuick/private/qsgshadersourcebuilder_p.h>
 #include <QtQuick/private/qsgtexture_p.h>
+#include <QtCore/qmutex.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -348,7 +349,10 @@ uint qHash(const QQuickShaderEffectMaterialKey &key)
 }
 
 
-QHash<QQuickShaderEffectMaterialKey, QSharedPointer<QSGMaterialType> > QQuickShaderEffectMaterial::materialMap;
+typedef QHash<QQuickShaderEffectMaterialKey, QWeakPointer<QSGMaterialType> > MaterialHash;
+
+Q_GLOBAL_STATIC(MaterialHash, materialHash)
+Q_GLOBAL_STATIC(QMutex, materialHashMutex)
 
 QQuickShaderEffectMaterial::QQuickShaderEffectMaterial(QQuickShaderEffectNode *node)
     : cullMode(NoCulling)
@@ -403,12 +407,30 @@ int QQuickShaderEffectMaterial::compare(const QSGMaterial *o) const
 
 void QQuickShaderEffectMaterial::setProgramSource(const QQuickShaderEffectMaterialKey &source)
 {
+    QMutexLocker locker(materialHashMutex);
+    Q_UNUSED(locker);
+
     m_source = source;
     m_emittedLogChanged = false;
-    m_type = materialMap.value(m_source);
+    QWeakPointer<QSGMaterialType> weakPtr = materialHash->value(m_source);
+    m_type = weakPtr.toStrongRef();
+
     if (m_type.isNull()) {
         m_type = QSharedPointer<QSGMaterialType>(new QSGMaterialType);
-        materialMap.insert(m_source, m_type);
+        materialHash->insert(m_source, m_type.toWeakRef());
+    }
+}
+
+void QQuickShaderEffectMaterial::cleanupMaterialCache()
+{
+    QMutexLocker locker(materialHashMutex);
+    Q_UNUSED(locker);
+
+    for (MaterialHash::iterator it = materialHash->begin(); it != materialHash->end(); ) {
+        if (!it.value().toStrongRef())
+            it = materialHash->erase(it);
+        else
+            ++it;
     }
 }
 
diff --git a/src/quick/items/qquickshadereffectnode_p.h b/src/quick/items/qquickshadereffectnode_p.h
index 7e3cf74276..28382c483c 100644
--- a/src/quick/items/qquickshadereffectnode_p.h
+++ b/src/quick/items/qquickshadereffectnode_p.h
@@ -101,6 +101,8 @@ public:
     void updateTextures() const;
     void invalidateTextureProvider(QSGTextureProvider *provider);
 
+    static void cleanupMaterialCache();
+
 protected:
     friend class QQuickCustomMaterialShader;
 
@@ -115,8 +117,6 @@ protected:
 
     QQuickShaderEffectNode *m_node;
     bool m_emittedLogChanged;
-
-    static QHash<QQuickShaderEffectMaterialKey, QSharedPointer<QSGMaterialType> > materialMap;
 };
 
 
diff --git a/src/quick/scenegraph/qsgrenderloop.cpp b/src/quick/scenegraph/qsgrenderloop.cpp
index ce3bf7d61d..b7a6475c23 100644
--- a/src/quick/scenegraph/qsgrenderloop.cpp
+++ b/src/quick/scenegraph/qsgrenderloop.cpp
@@ -52,6 +52,8 @@
 #include <QtQuick/private/qsgcontext_p.h>
 #include <private/qquickprofiler_p.h>
 
+#include <private/qquickshadereffectnode_p.h>
+
 #ifdef Q_OS_WIN
 #  include <QtCore/qt_windows.h>
 #endif
@@ -293,6 +295,8 @@ void QSGGuiThreadRenderLoop::windowDestroyed(QQuickWindow *window)
     if (Q_UNLIKELY(!current))
         qCDebug(QSG_LOG_RENDERLOOP) << "cleanup without an OpenGL context";
 
+    QQuickShaderEffectMaterial::cleanupMaterialCache();
+
     d->cleanupNodesOnShutdown();
     if (m_windows.size() == 0) {
         rc->invalidate();
diff --git a/src/quick/scenegraph/qsgthreadedrenderloop.cpp b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
index 7b1e24246b..26a0e78254 100644
--- a/src/quick/scenegraph/qsgthreadedrenderloop.cpp
+++ b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
@@ -56,6 +56,8 @@
 #include <private/qquickprofiler_p.h>
 #include <private/qqmldebugservice_p.h>
 
+#include <private/qquickshadereffectnode_p.h>
+
 /*
    Overall design:
 
@@ -449,6 +451,8 @@ void QSGRenderThread::invalidateOpenGL(QQuickWindow *window, bool inDestructor,
         qCDebug(QSG_LOG_RENDERLOOP) << QSG_RT_PAD << "- cleanup without an OpenGL context";
     }
 
+    QQuickShaderEffectMaterial::cleanupMaterialCache();
+
     // The canvas nodes must be cleaned up regardless if we are in the destructor..
     if (wipeSG) {
         QQuickWindowPrivate *dd = QQuickWindowPrivate::get(window);
diff --git a/src/quick/scenegraph/qsgwindowsrenderloop.cpp b/src/quick/scenegraph/qsgwindowsrenderloop.cpp
index 0e22fa8b7b..309e877dae 100644
--- a/src/quick/scenegraph/qsgwindowsrenderloop.cpp
+++ b/src/quick/scenegraph/qsgwindowsrenderloop.cpp
@@ -48,6 +48,8 @@
 
 #include <private/qquickprofiler_p.h>
 
+#include <private/qquickshadereffectnode_p.h>
+
 QT_BEGIN_NAMESPACE
 
 extern Q_GUI_EXPORT QImage qt_gl_read_framebuffer(const QSize &size, bool alpha_format, bool include_alpha);
@@ -232,6 +234,8 @@ void QSGWindowsRenderLoop::windowDestroyed(QQuickWindow *window)
     if (Q_UNLIKELY(!current))
         qCDebug(QSG_LOG_RENDERLOOP) << "cleanup without an OpenGL context";
 
+    QQuickShaderEffectMaterial::cleanupMaterialCache();
+
     d->cleanupNodesOnShutdown();
     if (m_windows.size() == 0) {
         d->context->invalidate();