Structural cleanup and improvements for the compositor.

Many parts of the compositor are unnecessarily complicated. This patch
aims at reducing the complexity of writing nodes and making the code
more transparent.

== Separating Nodes and Operations ==

Currently these are both mixed in the same graph, even though they have
very different purposes and are used at distinct stages in the
compositing process. The patch introduces dedicated graph classes for
nodes and for operations.

This removes the need for a lot of special case checks (isOperation etc.)
and explicit type casts. It simplifies the code since it becomes clear
at every stage what type of node we are dealing with. The compiler can
use static typing to avoid common bugs from mixing up these types and
fewer runtime sanity checks are needed.

== Simplified Node Conversion ==

Converting nodes to operations was previously based on "relinking", i.e.
nodes would start with by mirroring links in the Blender DNA node trees,
then add operations and redirect these links to them. This was very hard
to follow in many cases and required a lot of attention to avoid invalid
states.

Now there is a helper class called the NodeConverter, which is passed to
nodes and implements a much simpler API for this process. Nodes can add
operations and explicit connections as before, but defining "external"
links to the inputs/outputs of the original node now uses mapping
instead of directly modifying link data. Input data (node graph) and
result (operations graph) are cleanly separated.

== Removed Redundant Data Structures ==

A few redundant data structures have been removed, notably the
SocketConnection. These are only needed temporarily during graph
construction. For executing the compositor operations it is perfectly
sufficient to store only the direct input link pointers. A common
pointer indirection is avoided this way (which might also give a little
performance improvement).

== Avoid virtual recursive functions ==

Recursive virtual functions are evil. They are very hard to follow
during debugging. At least in the parts this patch is concerned with
these functions have been replaced by a non-virtual recursive core
function (which might then call virtual non-recursive functions if
needed). See for example NodeOperationBuilder::group_operations.

1 files changed, 661 insertions, 0 deletions

diff --git a/source/blender/compositor/intern/COM_NodeOperationBuilder.cpp b/source/blender/compositor/intern/COM_NodeOperationBuilder.cpp
new file mode 100644
index 00000000000..2807c25d7f5
--- /dev/null
+++ b/source/blender/compositor/intern/COM_NodeOperationBuilder.cpp
@@ -0,0 +1,661 @@
+/*
+ * Copyright 2013, Blender Foundation.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * Contributor: 
+ *		Lukas Toenne
+ */
+
+extern "C" {
+#include "BLI_utildefines.h"
+}
+
+#include "COM_NodeConverter.h"
+#include "COM_Converter.h"
+#include "COM_Debug.h"
+#include "COM_ExecutionSystem.h"
+#include "COM_Node.h"
+#include "COM_SocketProxyNode.h"
+
+#include "COM_NodeOperation.h"
+#include "COM_PreviewOperation.h"
+#include "COM_SetValueOperation.h"
+#include "COM_SetVectorOperation.h"
+#include "COM_SetColorOperation.h"
+#include "COM_SocketProxyOperation.h"
+#include "COM_ReadBufferOperation.h"
+#include "COM_WriteBufferOperation.h"
+
+#include "COM_NodeOperationBuilder.h" /* own include */
+
+NodeOperationBuilder::NodeOperationBuilder(const CompositorContext *context, bNodeTree *b_nodetree) :
+    m_context(context),
+    m_current_node(NULL)
+{
+	m_graph.from_bNodeTree(*context, b_nodetree);
+}
+
+NodeOperationBuilder::~NodeOperationBuilder()
+{
+}
+
+void NodeOperationBuilder::convertToOperations(ExecutionSystem *system)
+{
+	/* interface handle for nodes */
+	NodeConverter converter(this);
+	
+	for (int index = 0; index < m_graph.nodes().size(); index++) {
+		Node *node = (Node *)m_graph.nodes()[index];
+		
+		m_current_node = node;
+		
+		DebugInfo::node_to_operations(node);
+		node->convertToOperations(converter, *m_context);
+	}
+	
+	m_current_node = NULL;
+	
+	/* The input map constructed by nodes maps operation inputs to node inputs.
+	 * Inverting yields a map of node inputs to all connected operation inputs,
+	 * so multiple operations can use the same node input.
+	 */
+	OpInputInverseMap inverse_input_map;
+	for (InputSocketMap::const_iterator it = m_input_map.begin(); it != m_input_map.end(); ++it)
+		inverse_input_map[it->second].push_back(it->first);
+	
+	for (NodeGraph::Links::const_iterator it = m_graph.links().begin(); it != m_graph.links().end(); ++it) {
+		const NodeGraph::Link &link = *it;
+		NodeOutput *from = link.getFromSocket();
+		NodeInput *to = link.getToSocket();
+		
+		NodeOperationOutput *op_from = find_operation_output(m_output_map, from);
+		const OpInputs &op_to_list = find_operation_inputs(inverse_input_map, to);
+		if (!op_from || op_to_list.empty()) {
+			/* XXX allow this? error/debug message? */
+			BLI_assert(false);
+			continue;
+		}
+		
+		for (OpInputs::const_iterator it = op_to_list.begin(); it != op_to_list.end(); ++it) {
+			NodeOperationInput *op_to = *it;
+			addLink(op_from, op_to);
+		}
+	}
+	
+	add_datatype_conversions();
+	
+	add_operation_input_constants();
+	
+	resolve_proxies();
+	
+	determineResolutions();
+	
+	/* surround complex ops with read/write buffer */
+	add_complex_operation_buffers();
+	
+	/* links not available from here on */
+	/* XXX make m_links a local variable to avoid confusion! */
+	m_links.clear();
+	
+	prune_operations();
+	
+	/* ensure topological (link-based) order of nodes */
+	/*sort_operations();*/ /* not needed yet */
+	
+	/* create execution groups */
+	group_operations();
+	
+	/* transfer resulting operations to the system */
+	system->set_operations(m_operations, m_groups);
+}
+
+void NodeOperationBuilder::addOperation(NodeOperation *operation)
+{
+	m_operations.push_back(operation);
+}
+
+void NodeOperationBuilder::mapInputSocket(NodeInput *node_socket, NodeOperationInput *operation_socket)
+{
+	BLI_assert(m_current_node);
+	BLI_assert(node_socket->getNode() == m_current_node);
+	
+	/* note: this maps operation sockets to node sockets.
+	 * for resolving links the map will be inverted first in convertToOperations,
+	 * to get a list of links for each node input socket.
+	 */
+	m_input_map[operation_socket] = node_socket;
+}
+
+void NodeOperationBuilder::mapOutputSocket(NodeOutput *node_socket, NodeOperationOutput *operation_socket)
+{
+	BLI_assert(m_current_node);
+	BLI_assert(node_socket->getNode() == m_current_node);
+	
+	m_output_map[node_socket] = operation_socket;
+}
+
+void NodeOperationBuilder::addLink(NodeOperationOutput *from, NodeOperationInput *to)
+{
+	if (to->isConnected())
+		return;
+	
+	m_links.push_back(Link(from, to));
+	
+	/* register with the input */
+	to->setLink(from);
+}
+
+void NodeOperationBuilder::removeInputLink(NodeOperationInput *to)
+{
+	for (Links::iterator it = m_links.begin(); it != m_links.end(); ++it) {
+		Link &link = *it;
+		if (link.to() == to) {
+			/* unregister with the input */
+			to->setLink(NULL);
+			
+			m_links.erase(it);
+			return;
+		}
+	}
+}
+
+NodeInput *NodeOperationBuilder::find_node_input(const InputSocketMap &map, NodeOperationInput *op_input)
+{
+	InputSocketMap::const_iterator it = map.find(op_input);
+	return (it != map.end() ? it->second : NULL);
+}
+
+const NodeOperationBuilder::OpInputs &NodeOperationBuilder::find_operation_inputs(const OpInputInverseMap &map, NodeInput *node_input)
+{
+	static const OpInputs empty_list;
+	OpInputInverseMap::const_iterator it = map.find(node_input);
+	return (it != map.end() ? it->second : empty_list);
+}
+
+NodeOperationOutput *NodeOperationBuilder::find_operation_output(const OutputSocketMap &map, NodeOutput *node_output)
+{
+	OutputSocketMap::const_iterator it = map.find(node_output);
+	return (it != map.end() ? it->second : NULL);
+}
+
+PreviewOperation *NodeOperationBuilder::make_preview_operation() const
+{
+	BLI_assert(m_current_node);
+	
+	if (!(m_current_node->getbNode()->flag & NODE_PREVIEW))
+		return NULL;
+	/* previews only in the active group */
+	if (!m_current_node->isInActiveGroup())
+		return NULL;
+	/* do not calculate previews of hidden nodes */
+	if (m_current_node->getbNode()->flag & NODE_HIDDEN)
+		return NULL;
+	
+	bNodeInstanceHash *previews = m_context->getPreviewHash();
+	if (previews) {
+		PreviewOperation *operation = new PreviewOperation(m_context->getViewSettings(), m_context->getDisplaySettings());
+		operation->setbNodeTree(m_context->getbNodeTree());
+		operation->verifyPreview(previews, m_current_node->getInstanceKey());
+		return operation;
+	}
+	
+	return NULL;
+}
+
+void NodeOperationBuilder::addPreview(NodeOperationOutput *output)
+{
+	PreviewOperation *operation = make_preview_operation();
+	if (operation) {
+		addOperation(operation);
+		
+		addLink(output, operation->getInputSocket(0));
+	}
+}
+
+void NodeOperationBuilder::addNodeInputPreview(NodeInput *input)
+{
+	PreviewOperation *operation = make_preview_operation();
+	if (operation) {
+		addOperation(operation);
+		
+		mapInputSocket(input, operation->getInputSocket(0));
+	}
+}
+
+/****************************
+ **** Optimization Steps ****
+ ****************************/
+
+void NodeOperationBuilder::add_datatype_conversions()
+{
+	Links convert_links;
+	for (Links::const_iterator it = m_links.begin(); it != m_links.end(); ++it) {
+		const Link &link = *it;
+		if (link.from()->getDataType() != link.to()->getDataType())
+			convert_links.push_back(link);
+	}
+	for (Links::const_iterator it = convert_links.begin(); it != convert_links.end(); ++it) {
+		const Link &link = *it;
+		NodeOperation *converter = Converter::convertDataType(link.from(), link.to());
+		if (converter) {
+			addOperation(converter);
+			
+			removeInputLink(link.to());
+			addLink(link.from(), converter->getInputSocket(0));
+			addLink(converter->getOutputSocket(0), link.to());
+		}
+	}
+}
+
+void NodeOperationBuilder::add_operation_input_constants()
+{
+	/* Note: unconnected inputs cached first to avoid modifying
+	 *       m_operations while iterating over it
+	 */
+	typedef std::vector<NodeOperationInput*> Inputs;
+	Inputs pending_inputs;
+	for (Operations::const_iterator it = m_operations.begin(); it != m_operations.end(); ++it) {
+		NodeOperation *op = *it;
+		for (int k = 0; k < op->getNumberOfInputSockets(); ++k) {
+			NodeOperationInput *input = op->getInputSocket(k);
+			if (!input->isConnected())
+				pending_inputs.push_back(input);
+		}
+	}
+	for (Inputs::const_iterator it = pending_inputs.begin(); it != pending_inputs.end(); ++it) {
+		NodeOperationInput *input = *it;
+		add_input_constant_value(input, find_node_input(m_input_map, input));
+	}
+}
+
+void NodeOperationBuilder::add_input_constant_value(NodeOperationInput *input, NodeInput *node_input)
+{
+	switch (input->getDataType()) {
+		case COM_DT_VALUE: {
+			float value;
+			if (node_input && node_input->getbNodeSocket())
+				value = node_input->getEditorValueFloat();
+			else
+				value = 0.0f;
+			
+			SetValueOperation *op = new SetValueOperation();
+			op->setValue(value);
+			addOperation(op);
+			addLink(op->getOutputSocket(), input);
+			break;
+		}
+		case COM_DT_COLOR: {
+			float value[4];
+			if (node_input && node_input->getbNodeSocket())
+				node_input->getEditorValueColor(value);
+			else
+				zero_v4(value);
+			
+			SetColorOperation *op = new SetColorOperation();
+			op->setChannels(value);
+			addOperation(op);
+			addLink(op->getOutputSocket(), input);
+			break;
+		}
+		case COM_DT_VECTOR: {
+			float value[3];
+			if (node_input && node_input->getbNodeSocket())
+				node_input->getEditorValueVector(value);
+			else
+				zero_v3(value);
+			
+			SetVectorOperation *op = new SetVectorOperation();
+			op->setVector(value);
+			addOperation(op);
+			addLink(op->getOutputSocket(), input);
+			break;
+		}
+	}
+}
+
+void NodeOperationBuilder::resolve_proxies()
+{
+	Links proxy_links;
+	for (Links::const_iterator it = m_links.begin(); it != m_links.end(); ++it) {
+		const Link &link = *it;
+		/* don't replace links from proxy to proxy, since we may need them for replacing others! */
+		if (link.from()->getOperation().isProxyOperation() &&
+		    !link.to()->getOperation().isProxyOperation()) {
+			proxy_links.push_back(link);
+		}
+	}
+	
+	for (Links::const_iterator it = proxy_links.begin(); it != proxy_links.end(); ++it) {
+		const Link &link = *it;
+		
+		NodeOperationInput *to = link.to();
+		NodeOperationOutput *from = link.from();
+		do {
+			/* walk upstream bypassing the proxy operation */
+			from = from->getOperation().getInputSocket(0)->getLink();
+		} while (from && from->getOperation().isProxyOperation());
+		
+		removeInputLink(to);
+		/* we may not have a final proxy input link,
+		 * in that case it just gets dropped
+		 */
+		if (from)
+			addLink(from, to);
+	}
+}
+
+void NodeOperationBuilder::determineResolutions()
+{
+	/* determine all resolutions of the operations (Width/Height) */
+	for (Operations::const_iterator it = m_operations.begin(); it != m_operations.end(); ++it) {
+		NodeOperation *op = *it;
+		
+		if (op->isOutputOperation(m_context->isRendering()) && !op->isPreviewOperation()) {
+			unsigned int resolution[2] = {0, 0};
+			unsigned int preferredResolution[2] = {0, 0};
+			op->determineResolution(resolution, preferredResolution);
+			op->setResolution(resolution);
+		}
+	}
+	
+	for (Operations::const_iterator it = m_operations.begin(); it != m_operations.end(); ++it) {
+		NodeOperation *op = *it;
+		
+		if (op->isOutputOperation(m_context->isRendering()) && op->isPreviewOperation()) {
+			unsigned int resolution[2] = {0, 0};
+			unsigned int preferredResolution[2] = {0, 0};
+			op->determineResolution(resolution, preferredResolution);
+			op->setResolution(resolution);
+		}
+	}
+	
+	/* add convert resolution operations when needed */
+	{
+		Links convert_links;
+		for (Links::const_iterator it = m_links.begin(); it != m_links.end(); ++it) {
+			const Link &link = *it;
+			
+			if (link.to()->getResizeMode() != COM_SC_NO_RESIZE) {
+				NodeOperation &from_op = link.from()->getOperation();
+				NodeOperation &to_op = link.to()->getOperation();
+				if (from_op.getWidth() != to_op.getWidth() || from_op.getHeight() != to_op.getHeight())
+					convert_links.push_back(link);
+			}
+		}
+		for (Links::const_iterator it = convert_links.begin(); it != convert_links.end(); ++it) {
+			const Link &link = *it;
+			Converter::convertResolution(*this, link.from(), link.to());
+		}
+	}
+}
+
+NodeOperationBuilder::OpInputs NodeOperationBuilder::cache_output_links(NodeOperationOutput *output) const
+{
+	OpInputs inputs;
+	for (Links::const_iterator it = m_links.begin(); it != m_links.end(); ++it) {
+		const Link &link = *it;
+		if (link.from() == output)
+			inputs.push_back(link.to());
+	}
+	return inputs;
+}
+
+WriteBufferOperation *NodeOperationBuilder::find_attached_write_buffer_operation(NodeOperationOutput *output) const
+{
+	for (Links::const_iterator it = m_links.begin(); it != m_links.end(); ++it) {
+		const Link &link = *it;
+		if (link.from() == output) {
+			NodeOperation &op = link.to()->getOperation();
+			if (op.isWriteBufferOperation())
+				return (WriteBufferOperation *)(&op);
+		}
+	}
+	return NULL;
+}
+
+void NodeOperationBuilder::add_input_buffers(NodeOperation *operation, NodeOperationInput *input)
+{
+	if (!input->isConnected())
+		return;
+	
+	NodeOperationOutput *output = input->getLink();
+	if (output->getOperation().isReadBufferOperation()) {
+		/* input is already buffered, no need to add another */
+		return;
+	}
+	
+	/* this link will be replaced below */
+	removeInputLink(input);
+	
+	/* check of other end already has write operation, otherwise add a new one */
+	WriteBufferOperation *writeoperation = find_attached_write_buffer_operation(output);
+	if (!writeoperation) {
+		writeoperation = new WriteBufferOperation();
+		writeoperation->setbNodeTree(m_context->getbNodeTree());
+		addOperation(writeoperation);
+		
+		addLink(output, writeoperation->getInputSocket(0));
+		
+		writeoperation->readResolutionFromInputSocket();
+	}
+	
+	/* add readbuffer op for the input */
+	ReadBufferOperation *readoperation = new ReadBufferOperation();
+	readoperation->setMemoryProxy(writeoperation->getMemoryProxy());
+	this->addOperation(readoperation);
+	
+	addLink(readoperation->getOutputSocket(), input);
+	
+	readoperation->readResolutionFromWriteBuffer();
+}
+
+void NodeOperationBuilder::add_output_buffers(NodeOperation *operation, NodeOperationOutput *output)
+{
+	/* cache connected sockets, so we can safely remove links first before replacing them */
+	OpInputs targets = cache_output_links(output);
+	if (targets.empty())
+		return;
+	
+	WriteBufferOperation *writeOperation = NULL;
+	for (OpInputs::const_iterator it = targets.begin(); it != targets.end(); ++it) {
+		NodeOperationInput *target = *it;
+		
+		/* try to find existing write buffer operation */
+		if (target->getOperation().isWriteBufferOperation()) {
+			BLI_assert(writeOperation == NULL); /* there should only be one write op connected */
+			writeOperation = (WriteBufferOperation *)(&target->getOperation());
+		}
+		else {
+			/* remove all links to other nodes */
+			removeInputLink(target);
+		}
+	}
+	
+	/* if no write buffer operation exists yet, create a new one */
+	if (!writeOperation) {
+		writeOperation = new WriteBufferOperation();
+		writeOperation->setbNodeTree(m_context->getbNodeTree());
+		addOperation(writeOperation);
+		
+		addLink(output, writeOperation->getInputSocket(0));
+	}
+	
+	writeOperation->readResolutionFromInputSocket();
+	
+	/* add readbuffer op for every former connected input */
+	for (OpInputs::const_iterator it = targets.begin(); it != targets.end(); ++it) {
+		NodeOperationInput *target = *it;
+		if (&target->getOperation() == writeOperation)
+			continue; /* skip existing write op links */
+		
+		ReadBufferOperation *readoperation = new ReadBufferOperation();
+		readoperation->setMemoryProxy(writeOperation->getMemoryProxy());
+		addOperation(readoperation);
+		
+		addLink(readoperation->getOutputSocket(), target);
+	
+		readoperation->readResolutionFromWriteBuffer();
+	}
+}
+
+void NodeOperationBuilder::add_complex_operation_buffers()
+{
+	/* note: complex ops and get cached here first, since adding operations
+	 * will invalidate iterators over the main m_operations
+	 */
+	Operations complex_ops;
+	for (Operations::const_iterator it = m_operations.begin(); it != m_operations.end(); ++it)
+		if ((*it)->isComplex())
+			complex_ops.push_back(*it);
+	
+	for (Operations::const_iterator it = complex_ops.begin(); it != complex_ops.end(); ++it) {
+		NodeOperation *op = *it;
+		
+		DebugInfo::operation_read_write_buffer(op);
+		
+		for (int index = 0; index < op->getNumberOfInputSockets(); index++)
+			add_input_buffers(op, op->getInputSocket(index));
+		
+		for (int index = 0; index < op->getNumberOfOutputSockets(); index++)
+			add_output_buffers(op, op->getOutputSocket(index));
+	}
+}
+
+typedef std::set<NodeOperation*> Tags;
+
+static void find_reachable_operations_recursive(Tags &reachable, NodeOperation *op)
+{
+	if (reachable.find(op) != reachable.end())
+		return;
+	reachable.insert(op);
+	
+	for (int i = 0; i < op->getNumberOfInputSockets(); ++i) {
+		NodeOperationInput *input = op->getInputSocket(i);
+		if (input->isConnected())
+			find_reachable_operations_recursive(reachable, &input->getLink()->getOperation());
+	}
+	
+	/* associated write-buffer operations are executed as well */
+	if (op->isReadBufferOperation()) {
+		ReadBufferOperation *read_op = (ReadBufferOperation *)op;
+		MemoryProxy *memproxy = read_op->getMemoryProxy();
+		find_reachable_operations_recursive(reachable, memproxy->getWriteBufferOperation());
+	}
+}
+
+void NodeOperationBuilder::prune_operations()
+{
+	Tags reachable;
+	for (Operations::const_iterator it = m_operations.begin(); it != m_operations.end(); ++it) {
+		NodeOperation *op = *it;
+		
+		/* output operations are primary executed operations */
+		if (op->isOutputOperation(m_context->isRendering()))
+			find_reachable_operations_recursive(reachable, op);
+	}
+	
+	/* delete unreachable operations */
+	Operations reachable_ops;
+	for (Operations::const_iterator it = m_operations.begin(); it != m_operations.end(); ++it) {
+		NodeOperation *op = *it;
+		
+		if (reachable.find(op) != reachable.end())
+			reachable_ops.push_back(op);
+		else
+			delete op;
+	}
+	/* finally replace the operations list with the pruned list */
+	m_operations = reachable_ops;
+}
+
+/* topological (depth-first) sorting of operations */
+static void sort_operations_recursive(NodeOperationBuilder::Operations &sorted, Tags &visited, NodeOperation *op)
+{
+	if (visited.find(op) != visited.end())
+		return;
+	visited.insert(op);
+	
+	for (int i = 0; i < op->getNumberOfInputSockets(); ++i) {
+		NodeOperationInput *input = op->getInputSocket(i);
+		if (input->isConnected())
+			sort_operations_recursive(sorted, visited, &input->getLink()->getOperation());
+	}
+	
+	sorted.push_back(op);
+}
+
+void NodeOperationBuilder::sort_operations()
+{
+	Operations sorted;
+	sorted.reserve(m_operations.size());
+	Tags visited;
+	
+	for (Operations::const_iterator it = m_operations.begin(); it != m_operations.end(); ++it)
+		sort_operations_recursive(sorted, visited, *it);
+	
+	m_operations = sorted;
+}
+
+static void add_group_operations_recursive(Tags &visited, NodeOperation *op, ExecutionGroup *group)
+{
+	if (visited.find(op) != visited.end())
+		return;
+	visited.insert(op);
+	
+	if (!group->addOperation(op))
+		return;
+	
+	/* add all eligible input ops to the group */
+	for (int i = 0; i < op->getNumberOfInputSockets(); ++i) {
+		NodeOperationInput *input = op->getInputSocket(i);
+		if (input->isConnected())
+			add_group_operations_recursive(visited, &input->getLink()->getOperation(), group);
+	}
+}
+
+ExecutionGroup *NodeOperationBuilder::make_group(NodeOperation *op)
+{
+	ExecutionGroup *group = new ExecutionGroup();
+	m_groups.push_back(group);
+	
+	Tags visited;
+	add_group_operations_recursive(visited, op, group);
+	
+	return group;
+}
+
+void NodeOperationBuilder::group_operations()
+{
+	for (Operations::const_iterator it = m_operations.begin(); it != m_operations.end(); ++it) {
+		NodeOperation *op = *it;
+		
+		if (op->isOutputOperation(m_context->isRendering())) {
+			ExecutionGroup *group = make_group(op);
+			group->setOutputExecutionGroup(true);
+		}
+		
+		/* add new groups for associated memory proxies where needed */
+		if (op->isReadBufferOperation()) {
+			ReadBufferOperation *read_op = (ReadBufferOperation *)op;
+			MemoryProxy *memproxy = read_op->getMemoryProxy();
+			
+			if (memproxy->getExecutor() == NULL) {
+				ExecutionGroup *group = make_group(memproxy->getWriteBufferOperation());
+				memproxy->setExecutor(group);
+			}
+		}
+	}
+}