rhi: Enable registering cleanup callbacks with a key

And the ability to deregister.

Going to be required by QRhiWidget.

Change-Id: If185cbed2faa042098ac1f6bb1d6daaffd834377
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

src/gui/rhi/qrhi.cpp

@@ -8445,6 +8445,33 @@ void QRhi::addCleanupCallback(const CleanupCallback &callback)
     d->addCleanupCallback(callback);
 }
 
+/*!
+    \overload
+
+    Registers \a callback to be invoked either when the QRhi is destroyed or
+    when runCleanup() is called. This overload takes an opaque pointer, \a key,
+    that is used to ensure that a given callback is registered (and so called)
+    only once.
+
+    \sa removeCleanupCallback()
+ */
+void QRhi::addCleanupCallback(const void *key, const CleanupCallback &callback)
+{
+    d->addCleanupCallback(key, callback);
+}
+
+/*!
+    Deregisters the callback with \a key. If no cleanup callback was registered
+    with \a key, the function does nothing. Callbacks registered without a key
+    cannot be removed.
+
+    \sa addCleanupCallback()
+ */
+void QRhi::removeCleanupCallback(const void *key)
+{
+    d->removeCleanupCallback(key);
+}
+
 /*!
     Invokes all registered cleanup functions. The list of cleanup callbacks it
     then cleared. Normally destroying the QRhi does this automatically, but
@@ -8459,6 +8486,11 @@ void QRhi::runCleanup()
         f(this);
 
     d->cleanupCallbacks.clear();
+
+    for (auto it = d->keyedCleanupCallbacks.cbegin(), end = d->keyedCleanupCallbacks.cend(); it != end; ++it)
+        it.value()(this);
+
+    d->keyedCleanupCallbacks.clear();
 }
 
 /*!

src/gui/rhi/qrhi.h

@@ -1876,6 +1876,8 @@ public:
 
     using CleanupCallback = std::function<void(QRhi *)>;
     void addCleanupCallback(const CleanupCallback &callback);
+    void addCleanupCallback(const void *key, const CleanupCallback &callback);
+    void removeCleanupCallback(const void *key);
     void runCleanup();
 
     QRhiGraphicsPipeline *newGraphicsPipeline();

src/gui/rhi/qrhi_p.h

@@ -179,6 +179,16 @@ public:
         cleanupCallbacks.append(callback);
     }
 
+    void addCleanupCallback(const void *key, const QRhi::CleanupCallback &callback)
+    {
+        keyedCleanupCallbacks[key] = callback;
+    }
+
+    void removeCleanupCallback(const void *key)
+    {
+        keyedCleanupCallbacks.remove(key);
+    }
+
     bool sanityCheckGraphicsPipeline(QRhiGraphicsPipeline *ps);
     bool sanityCheckShaderResourceBindings(QRhiShaderResourceBindings *srb);
     void updateLayoutDesc(QRhiShaderResourceBindings *srb);
@@ -239,6 +249,7 @@ private:
     QHash<QRhiResource *, bool> resources;
     QSet<QRhiResource *> pendingDeleteResources;
     QVarLengthArray<QRhi::CleanupCallback, 4> cleanupCallbacks;
+    QHash<const void *, QRhi::CleanupCallback> keyedCleanupCallbacks;
     QElapsedTimer pipelineCreationTimer;
     qint64 accumulatedPipelineCreationTime = 0;