MeshUpdateQueue: Add a MapBlock cache that minimizes the amount of MapBlock copying done in the main thread

Cache size is configurable by the meshgen_block_cache_size (default 20 MB).

New profiler stats:
- MeshUpdateQueue MapBlock cache hit %
- MeshUpdateQueue MapBlock cache size kB

Removes one type of stutter that was seen on the client when received MapBlocks
were being handled. (the "MeshMakeData::fill" stutter)

Kind of related to at least #5239

Originally preceded by these commits, now includes them:
- Move the mesh generator thread into src/mesh_generator_thread.{cpp,h}
- mesh_generator_thread.cpp: Update code style
- MeshUpdateThread: Modify interface to house a different implementation: Actual functionality will be changed by next commits.
- MeshMakeData: Add fillBlockData() interface (so that caller can fill in stuff from eg. a MapBlock cache)

9 files changed, 514 insertions, 278 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index edb291545..37f72a44d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -522,6 +522,7 @@ set(client_SRCS
 	main.cpp
 	mapblock_mesh.cpp
 	mesh.cpp
+	mesh_generator_thread.cpp
 	minimap.cpp
 	particles.cpp
 	shader.cpp
diff --git a/src/client.cpp b/src/client.cpp
index 5ca51bd9c..7b962cd94 100644
--- a/src/client.cpp
+++ b/src/client.cpp
@@ -51,147 +51,6 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 extern gui::IGUIEnvironment* guienv;
 
 /*
-	QueuedMeshUpdate
-*/
-
-QueuedMeshUpdate::QueuedMeshUpdate():
-	p(-1337,-1337,-1337),
-	data(NULL),
-	ack_block_to_server(false)
-{
-}
-
-QueuedMeshUpdate::~QueuedMeshUpdate()
-{
-	if(data)
-		delete data;
-}
-
-/*
-	MeshUpdateQueue
-*/
-
-MeshUpdateQueue::MeshUpdateQueue()
-{
-}
-
-MeshUpdateQueue::~MeshUpdateQueue()
-{
-	MutexAutoLock lock(m_mutex);
-
-	for(std::vector<QueuedMeshUpdate*>::iterator
-			i = m_queue.begin();
-			i != m_queue.end(); ++i)
-	{
-		QueuedMeshUpdate *q = *i;
-		delete q;
-	}
-}
-
-/*
-	peer_id=0 adds with nobody to send to
-*/
-void MeshUpdateQueue::addBlock(v3s16 p, MeshMakeData *data, bool ack_block_to_server, bool urgent)
-{
-	DSTACK(FUNCTION_NAME);
-
-	assert(data);	// pre-condition
-
-	MutexAutoLock lock(m_mutex);
-
-	if(urgent)
-		m_urgents.insert(p);
-
-	/*
-		Find if block is already in queue.
-		If it is, update the data and quit.
-	*/
-	for(std::vector<QueuedMeshUpdate*>::iterator
-			i = m_queue.begin();
-			i != m_queue.end(); ++i)
-	{
-		QueuedMeshUpdate *q = *i;
-		if(q->p == p)
-		{
-			if(q->data)
-				delete q->data;
-			q->data = data;
-			if(ack_block_to_server)
-				q->ack_block_to_server = true;
-			return;
-		}
-	}
-
-	/*
-		Add the block
-	*/
-	QueuedMeshUpdate *q = new QueuedMeshUpdate;
-	q->p = p;
-	q->data = data;
-	q->ack_block_to_server = ack_block_to_server;
-	m_queue.push_back(q);
-}
-
-// Returned pointer must be deleted
-// Returns NULL if queue is empty
-QueuedMeshUpdate *MeshUpdateQueue::pop()
-{
-	MutexAutoLock lock(m_mutex);
-
-	bool must_be_urgent = !m_urgents.empty();
-	for(std::vector<QueuedMeshUpdate*>::iterator
-			i = m_queue.begin();
-			i != m_queue.end(); ++i)
-	{
-		QueuedMeshUpdate *q = *i;
-		if(must_be_urgent && m_urgents.count(q->p) == 0)
-			continue;
-		m_queue.erase(i);
-		m_urgents.erase(q->p);
-		return q;
-	}
-	return NULL;
-}
-
-/*
-	MeshUpdateThread
-*/
-
-MeshUpdateThread::MeshUpdateThread() : UpdateThread("Mesh")
-{
-	m_generation_interval = g_settings->getU16("mesh_generation_interval");
-	m_generation_interval = rangelim(m_generation_interval, 0, 50);
-}
-
-void MeshUpdateThread::enqueueUpdate(v3s16 p, MeshMakeData *data,
-		bool ack_block_to_server, bool urgent)
-{
-	m_queue_in.addBlock(p, data, ack_block_to_server, urgent);
-	deferUpdate();
-}
-
-void MeshUpdateThread::doUpdate()
-{
-	QueuedMeshUpdate *q;
-	while ((q = m_queue_in.pop())) {
-		if (m_generation_interval)
-			sleep_ms(m_generation_interval);
-		ScopeProfiler sp(g_profiler, "Client: Mesh making");
-
-		MapBlockMesh *mesh_new = new MapBlockMesh(q->data, m_camera_offset);
-
-		MeshUpdateResult r;
-		r.p = q->p;
-		r.mesh = mesh_new;
-		r.ack_block_to_server = q->ack_block_to_server;
-
-		m_queue_out.push_back(r);
-
-		delete q;
-	}
-}
-
-/*
 	Client
 */
 
@@ -220,7 +79,7 @@ Client::Client(
 	m_nodedef(nodedef),
 	m_sound(sound),
 	m_event(event),
-	m_mesh_update_thread(),
+	m_mesh_update_thread(this),
 	m_env(
 		new ClientMap(this, control,
 			device->getSceneManager()->getRootSceneNode(),
@@ -269,12 +128,6 @@ Client::Client(
 	m_minimap = new Minimap(device, this);
 	m_cache_save_interval = g_settings->getU16("server_map_save_interval");
 
-	m_cache_smooth_lighting = g_settings->getBool("smooth_lighting");
-	m_cache_enable_shaders  = g_settings->getBool("enable_shaders");
-	m_cache_use_tangent_vertices = m_cache_enable_shaders && (
-		g_settings->getBool("enable_bumpmapping") ||
-		g_settings->getBool("enable_parallax_occlusion"));
-
 	m_modding_enabled = g_settings->getBool("enable_client_modding");
 	m_script = new ClientScripting(this);
 	m_env.setScript(m_script);
@@ -1605,6 +1458,11 @@ int Client::getCrackLevel()
 	return m_crack_level;
 }
 
+v3s16 Client::getCrackPos()
+{
+	return m_crack_pos;
+}
+
 void Client::setCrack(int level, v3s16 pos)
 {
 	int old_crack_level = m_crack_level;
@@ -1670,28 +1528,14 @@ void Client::typeChatMessage(const std::wstring &message)
 
 void Client::addUpdateMeshTask(v3s16 p, bool ack_to_server, bool urgent)
 {
+	// Check if the block exists to begin with. In the case when a non-existing
+	// neighbor is automatically added, it may not. In that case we don't want
+	// to tell the mesh update thread about it.
 	MapBlock *b = m_env.getMap().getBlockNoCreateNoEx(p);
-	if(b == NULL)
+	if (b == NULL)
 		return;
 
-	/*
-		Create a task to update the mesh of the block
-	*/
-
-	MeshMakeData *data = new MeshMakeData(this, m_cache_enable_shaders,
-		m_cache_use_tangent_vertices);
-
-	{
-		//TimeTaker timer("data fill");
-		// Release: ~0ms
-		// Debug: 1-6ms, avg=2ms
-		data->fill(b);
-		data->setCrack(m_crack_level, m_crack_pos);
-		data->setSmoothLighting(m_cache_smooth_lighting);
-	}
-
-	// Add task to queue
-	m_mesh_update_thread.enqueueUpdate(p, data, ack_to_server, urgent);
+	m_mesh_update_thread.updateBlock(&m_env.getMap(), p, ack_to_server, urgent);
 }
 
 void Client::addUpdateMeshTaskWithEdge(v3s16 blockpos, bool ack_to_server, bool urgent)
diff --git a/src/client.h b/src/client.h
index e565acd93..e7fcb597d 100644
--- a/src/client.h
+++ b/src/client.h
@@ -36,6 +36,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "particles.h"
 #include "mapnode.h"
 #include "tileanimation.h"
+#include "mesh_generator_thread.h"
 
 struct MeshMakeData;
 class MapBlockMesh;
@@ -54,88 +55,12 @@ struct MinimapMapblock;
 class Camera;
 class NetworkPacket;
 
-struct QueuedMeshUpdate
-{
-	v3s16 p;
-	MeshMakeData *data;
-	bool ack_block_to_server;
-
-	QueuedMeshUpdate();
-	~QueuedMeshUpdate();
-};
-
 enum LocalClientState {
 	LC_Created,
 	LC_Init,
 	LC_Ready
 };
 
-/*
-	A thread-safe queue of mesh update tasks
-*/
-class MeshUpdateQueue
-{
-public:
-	MeshUpdateQueue();
-
-	~MeshUpdateQueue();
-
-	/*
-		peer_id=0 adds with nobody to send to
-	*/
-	void addBlock(v3s16 p, MeshMakeData *data,
-			bool ack_block_to_server, bool urgent);
-
-	// Returned pointer must be deleted
-	// Returns NULL if queue is empty
-	QueuedMeshUpdate * pop();
-
-	u32 size()
-	{
-		MutexAutoLock lock(m_mutex);
-		return m_queue.size();
-	}
-
-private:
-	std::vector<QueuedMeshUpdate*> m_queue;
-	std::set<v3s16> m_urgents;
-	Mutex m_mutex;
-};
-
-struct MeshUpdateResult
-{
-	v3s16 p;
-	MapBlockMesh *mesh;
-	bool ack_block_to_server;
-
-	MeshUpdateResult():
-		p(-1338,-1338,-1338),
-		mesh(NULL),
-		ack_block_to_server(false)
-	{
-	}
-};
-
-class MeshUpdateThread : public UpdateThread
-{
-private:
-	MeshUpdateQueue m_queue_in;
-	int m_generation_interval;
-
-protected:
-	virtual void doUpdate();
-
-public:
-
-	MeshUpdateThread();
-
-	void enqueueUpdate(v3s16 p, MeshMakeData *data,
-			bool ack_block_to_server, bool urgent);
-	MutexedQueue<MeshUpdateResult> m_queue_out;
-
-	v3s16 m_camera_offset;
-};
-
 enum ClientEventType
 {
 	CE_NONE,
@@ -471,6 +396,7 @@ public:
 	float getAnimationTime();
 
 	int getCrackLevel();
+	v3s16 getCrackPos();
 	void setCrack(int level, v3s16 pos);
 
 	u16 getHP();
@@ -726,11 +652,6 @@ private:
 	IntervalLimiter m_localdb_save_interval;
 	u16 m_cache_save_interval;
 
-	// TODO: Add callback to update these when g_settings changes
-	bool m_cache_smooth_lighting;
-	bool m_cache_enable_shaders;
-	bool m_cache_use_tangent_vertices;
-
 	ClientScripting *m_script;
 	bool m_modding_enabled;
 	UNORDERED_MAP<std::string, ModMetadata *> m_mod_storages;
diff --git a/src/defaultsettings.cpp b/src/defaultsettings.cpp
index c6ced5931..573b5e2d8 100644
--- a/src/defaultsettings.cpp
+++ b/src/defaultsettings.cpp
@@ -39,6 +39,7 @@ void set_default_settings(Settings *settings)
 	settings->setDefault("sound_volume", "0.8");
 	settings->setDefault("enable_mesh_cache", "false");
 	settings->setDefault("mesh_generation_interval", "0");
+	settings->setDefault("meshgen_block_cache_size", "20");
 	settings->setDefault("enable_vbo", "true");
 	settings->setDefault("free_move", "false");
 	settings->setDefault("fast_move", "false");
diff --git a/src/mapblock.h b/src/mapblock.h
index 7ff613fe8..8816dc817 100644
--- a/src/mapblock.h
+++ b/src/mapblock.h
@@ -154,6 +154,11 @@ public:
 		raiseModified(MOD_STATE_WRITE_NEEDED, MOD_REASON_REALLOCATE);
 	}
 
+	MapNode* getData()
+	{
+		return data;
+	}
+
 	////
 	//// Modification tracking methods
 	////
diff --git a/src/mapblock_mesh.cpp b/src/mapblock_mesh.cpp
index eddb061b4..933dfc32a 100644
--- a/src/mapblock_mesh.cpp
+++ b/src/mapblock_mesh.cpp
@@ -48,49 +48,43 @@ MeshMakeData::MeshMakeData(Client *client, bool use_shaders,
 	m_use_tangent_vertices(use_tangent_vertices)
 {}
 
-void MeshMakeData::fill(MapBlock *block)
+void MeshMakeData::fillBlockDataBegin(const v3s16 &blockpos)
 {
-	m_blockpos = block->getPos();
+	m_blockpos = blockpos;
 
 	v3s16 blockpos_nodes = m_blockpos*MAP_BLOCKSIZE;
 
-	/*
-		Copy data
-	*/
-
-	// Allocate this block + neighbors
 	m_vmanip.clear();
 	VoxelArea voxel_area(blockpos_nodes - v3s16(1,1,1) * MAP_BLOCKSIZE,
 			blockpos_nodes + v3s16(1,1,1) * MAP_BLOCKSIZE*2-v3s16(1,1,1));
 	m_vmanip.addArea(voxel_area);
+}
 
-	{
-		//TimeTaker timer("copy central block data");
-		// 0ms
+void MeshMakeData::fillBlockData(const v3s16 &block_offset, MapNode *data)
+{
+	v3s16 data_size(MAP_BLOCKSIZE, MAP_BLOCKSIZE, MAP_BLOCKSIZE);
+	VoxelArea data_area(v3s16(0,0,0), data_size - v3s16(1,1,1));
 
-		// Copy our data
-		block->copyTo(m_vmanip);
-	}
-	{
-		//TimeTaker timer("copy neighbor block data");
-		// 0ms
+	v3s16 bp = m_blockpos + block_offset;
+	v3s16 blockpos_nodes = bp * MAP_BLOCKSIZE;
+	m_vmanip.copyFrom(data, data_area, v3s16(0,0,0), blockpos_nodes, data_size);
+}
+
+void MeshMakeData::fill(MapBlock *block)
+{
+	fillBlockDataBegin(block->getPos());
 
-		/*
-			Copy neighbors. This is lightning fast.
-			Copying only the borders would be *very* slow.
-		*/
+	fillBlockData(v3s16(0,0,0), block->getData());
 
-		// Get map
-		Map *map = block->getParent();
+	// Get map for reading neigbhor blocks
+	Map *map = block->getParent();
 
-		for(u16 i=0; i<26; i++)
-		{
-			const v3s16 &dir = g_26dirs[i];
-			v3s16 bp = m_blockpos + dir;
-			MapBlock *b = map->getBlockNoCreateNoEx(bp);
-			if(b)
-				b->copyTo(m_vmanip);
-		}
+	for (u16 i=0; i<26; i++) {
+		const v3s16 &dir = g_26dirs[i];
+		v3s16 bp = m_blockpos + dir;
+		MapBlock *b = map->getBlockNoCreateNoEx(bp);
+		if(b)
+			fillBlockData(dir, b->getData());
 	}
 }
 
diff --git a/src/mapblock_mesh.h b/src/mapblock_mesh.h
index 916703f3e..25c699e1c 100644
--- a/src/mapblock_mesh.h
+++ b/src/mapblock_mesh.h
@@ -53,6 +53,12 @@ struct MeshMakeData
 			bool use_tangent_vertices = false);
 
 	/*
+		Copy block data manually (to allow optimizations by the caller)
+	*/
+	void fillBlockDataBegin(const v3s16 &blockpos);
+	void fillBlockData(const v3s16 &block_offset, MapNode *data);
+
+	/*
 		Copy central data directly from block, and other data from
 		parent of block.
 	*/
diff --git a/src/mesh_generator_thread.cpp b/src/mesh_generator_thread.cpp
new file mode 100644
index 000000000..126bf6327
--- /dev/null
+++ b/src/mesh_generator_thread.cpp
@@ -0,0 +1,329 @@
+/*
+Minetest
+Copyright (C) 2013, 2017 celeron55, Perttu Ahola <celeron55@gmail.com>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser 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.
+*/
+
+#include "mesh_generator_thread.h"
+#include "settings.h"
+#include "profiler.h"
+#include "client.h"
+#include "mapblock.h"
+#include "map.h"
+
+/*
+	CachedMapBlockData
+*/
+
+CachedMapBlockData::CachedMapBlockData():
+	p(-1337,-1337,-1337),
+	data(NULL),
+	refcount_from_queue(0),
+	last_used_timestamp(time(0))
+{
+}
+
+CachedMapBlockData::~CachedMapBlockData()
+{
+	assert(refcount_from_queue == 0);
+
+	if (data)
+		delete[] data;
+}
+
+/*
+	QueuedMeshUpdate
+*/
+
+QueuedMeshUpdate::QueuedMeshUpdate():
+	p(-1337,-1337,-1337),
+	ack_block_to_server(false),
+	urgent(false),
+	crack_level(-1),
+	crack_pos(0,0,0),
+	data(NULL)
+{
+}
+
+QueuedMeshUpdate::~QueuedMeshUpdate()
+{
+	if (data)
+		delete data;
+}
+
+/*
+	MeshUpdateQueue
+*/
+
+MeshUpdateQueue::MeshUpdateQueue(Client *client):
+	m_client(client)
+{
+	m_cache_enable_shaders = g_settings->getBool("enable_shaders");
+	m_cache_use_tangent_vertices = m_cache_enable_shaders && (
+		g_settings->getBool("enable_bumpmapping") ||
+		g_settings->getBool("enable_parallax_occlusion"));
+	m_cache_smooth_lighting = g_settings->getBool("smooth_lighting");
+	m_meshgen_block_cache_size = g_settings->getS32("meshgen_block_cache_size");
+}
+
+MeshUpdateQueue::~MeshUpdateQueue()
+{
+	MutexAutoLock lock(m_mutex);
+
+	for (std::vector<QueuedMeshUpdate*>::iterator i = m_queue.begin();
+			i != m_queue.end(); ++i) {
+		QueuedMeshUpdate *q = *i;
+		delete q;
+	}
+}
+
+void MeshUpdateQueue::addBlock(Map *map, v3s16 p, bool ack_block_to_server, bool urgent)
+{
+	DSTACK(FUNCTION_NAME);
+
+	MutexAutoLock lock(m_mutex);
+
+	cleanupCache();
+
+	/*
+		Cache the block data (force-update the center block, don't update the
+		neighbors but get them if they aren't already cached)
+	*/
+	std::vector<CachedMapBlockData*> cached_blocks;
+	size_t cache_hit_counter = 0;
+	cached_blocks.reserve(3*3*3);
+	v3s16 dp;
+	for (dp.X = -1; dp.X <= 1; dp.X++)
+	for (dp.Y = -1; dp.Y <= 1; dp.Y++)
+	for (dp.Z = -1; dp.Z <= 1; dp.Z++) {
+		v3s16 p1 = p + dp;
+		CachedMapBlockData *cached_block;
+		if (dp == v3s16(0, 0, 0))
+			cached_block = cacheBlock(map, p1, FORCE_UPDATE);
+		else
+			cached_block = cacheBlock(map, p1, SKIP_UPDATE_IF_ALREADY_CACHED,
+					&cache_hit_counter);
+		cached_blocks.push_back(cached_block);
+	}
+	g_profiler->avg("MeshUpdateQueue MapBlock cache hit %",
+			100.0f * cache_hit_counter / cached_blocks.size());
+
+	/*
+		Mark the block as urgent if requested
+	*/
+	if (urgent)
+		m_urgents.insert(p);
+
+	/*
+		Find if block is already in queue.
+		If it is, update the data and quit.
+	*/
+	for (std::vector<QueuedMeshUpdate*>::iterator i = m_queue.begin();
+			i != m_queue.end(); ++i) {
+		QueuedMeshUpdate *q = *i;
+		if (q->p == p) {
+			// NOTE: We are not adding a new position to the queue, thus
+			//       refcount_from_queue stays the same.
+			if(ack_block_to_server)
+				q->ack_block_to_server = true;
+			q->crack_level = m_client->getCrackLevel();
+			q->crack_pos = m_client->getCrackPos();
+			return;
+		}
+	}
+
+	/*
+		Add the block
+	*/
+	QueuedMeshUpdate *q = new QueuedMeshUpdate;
+	q->p = p;
+	q->ack_block_to_server = ack_block_to_server;
+	q->crack_level = m_client->getCrackLevel();
+	q->crack_pos = m_client->getCrackPos();
+	m_queue.push_back(q);
+
+	// This queue entry is a new reference to the cached blocks
+	for (size_t i=0; i<cached_blocks.size(); i++) {
+		cached_blocks[i]->refcount_from_queue++;
+	}
+}
+
+// Returned pointer must be deleted
+// Returns NULL if queue is empty
+QueuedMeshUpdate *MeshUpdateQueue::pop()
+{
+	MutexAutoLock lock(m_mutex);
+
+	bool must_be_urgent = !m_urgents.empty();
+	for (std::vector<QueuedMeshUpdate*>::iterator i = m_queue.begin();
+			i != m_queue.end(); ++i) {
+		QueuedMeshUpdate *q = *i;
+		if(must_be_urgent && m_urgents.count(q->p) == 0)
+			continue;
+		m_queue.erase(i);
+		m_urgents.erase(q->p);
+		fillDataFromMapBlockCache(q);
+		return q;
+	}
+	return NULL;
+}
+
+CachedMapBlockData* MeshUpdateQueue::cacheBlock(Map *map, v3s16 p, UpdateMode mode,
+			size_t *cache_hit_counter)
+{
+	std::map<v3s16, CachedMapBlockData*>::iterator it =
+			m_cache.find(p);
+	if (it != m_cache.end()) {
+		// Already in cache
+		CachedMapBlockData *cached_block = it->second;
+		if (mode == SKIP_UPDATE_IF_ALREADY_CACHED) {
+			if (cache_hit_counter)
+				(*cache_hit_counter)++;
+			return cached_block;
+		}
+		MapBlock *b = map->getBlockNoCreateNoEx(p);
+		if (b) {
+			if (cached_block->data == NULL)
+				cached_block->data =
+						new MapNode[MAP_BLOCKSIZE * MAP_BLOCKSIZE * MAP_BLOCKSIZE];
+			memcpy(cached_block->data, b->getData(),
+					MAP_BLOCKSIZE * MAP_BLOCKSIZE * MAP_BLOCKSIZE * sizeof(MapNode));
+		} else {
+			delete[] cached_block->data;
+			cached_block->data = NULL;
+		}
+		return cached_block;
+	} else {
+		// Not yet in cache
+		CachedMapBlockData *cached_block = new CachedMapBlockData();
+		m_cache[p] = cached_block;
+		MapBlock *b = map->getBlockNoCreateNoEx(p);
+		if (b) {
+			cached_block->data =
+					new MapNode[MAP_BLOCKSIZE * MAP_BLOCKSIZE * MAP_BLOCKSIZE];
+			memcpy(cached_block->data, b->getData(),
+					MAP_BLOCKSIZE * MAP_BLOCKSIZE * MAP_BLOCKSIZE * sizeof(MapNode));
+		}
+		return cached_block;
+	}
+}
+
+CachedMapBlockData* MeshUpdateQueue::getCachedBlock(const v3s16 &p)
+{
+	std::map<v3s16, CachedMapBlockData*>::iterator it = m_cache.find(p);
+	if (it != m_cache.end()) {
+		return it->second;
+	}
+	return NULL;
+}
+
+void MeshUpdateQueue::fillDataFromMapBlockCache(QueuedMeshUpdate *q)
+{
+	MeshMakeData *data = new MeshMakeData(m_client, m_cache_enable_shaders,
+			m_cache_use_tangent_vertices);
+	q->data = data;
+
+	data->fillBlockDataBegin(q->p);
+
+	int t_now = time(0);
+
+	// Collect data for 3*3*3 blocks from cache
+	v3s16 dp;
+	for (dp.X = -1; dp.X <= 1; dp.X++)
+	for (dp.Y = -1; dp.Y <= 1; dp.Y++)
+	for (dp.Z = -1; dp.Z <= 1; dp.Z++) {
+		v3s16 p = q->p + dp;
+		CachedMapBlockData *cached_block = getCachedBlock(p);
+		if (cached_block) {
+			cached_block->refcount_from_queue--;
+			cached_block->last_used_timestamp = t_now;
+			if (cached_block->data)
+				data->fillBlockData(dp, cached_block->data);
+		}
+	}
+
+	data->setCrack(q->crack_level, q->crack_pos);
+	data->setSmoothLighting(m_cache_smooth_lighting);
+}
+
+void MeshUpdateQueue::cleanupCache()
+{
+	const int mapblock_kB = MAP_BLOCKSIZE * MAP_BLOCKSIZE * MAP_BLOCKSIZE *
+			sizeof(MapNode) / 1000;
+	g_profiler->avg("MeshUpdateQueue MapBlock cache size kB",
+			mapblock_kB * m_cache.size());
+
+	// The cache size is kept roughly below cache_soft_max_size, not letting
+	// anything get older than cache_seconds_max or deleted before 2 seconds.
+	const int cache_seconds_max = 10;
+	const int cache_soft_max_size = m_meshgen_block_cache_size * 1000 / mapblock_kB;
+	int cache_seconds = MYMAX(2, cache_seconds_max -
+			m_cache.size() / (cache_soft_max_size / cache_seconds_max));
+
+	int t_now = time(0);
+
+	for (std::map<v3s16, CachedMapBlockData*>::iterator it = m_cache.begin();
+			it != m_cache.end(); ) {
+		CachedMapBlockData *cached_block = it->second;
+		if (cached_block->refcount_from_queue == 0 &&
+				cached_block->last_used_timestamp < t_now - cache_seconds) {
+			m_cache.erase(it++);
+		} else {
+			++it;
+		}
+	}
+}
+
+/*
+	MeshUpdateThread
+*/
+
+MeshUpdateThread::MeshUpdateThread(Client *client):
+	UpdateThread("Mesh"),
+	m_queue_in(client)
+{
+	m_generation_interval = g_settings->getU16("mesh_generation_interval");
+	m_generation_interval = rangelim(m_generation_interval, 0, 50);
+}
+
+void MeshUpdateThread::updateBlock(Map *map, v3s16 p, bool ack_block_to_server,
+		bool urgent)
+{
+	// Allow the MeshUpdateQueue to do whatever it wants
+	m_queue_in.addBlock(map, p, ack_block_to_server, urgent);
+	deferUpdate();
+}
+
+void MeshUpdateThread::doUpdate()
+{
+	QueuedMeshUpdate *q;
+	while ((q = m_queue_in.pop())) {
+		if (m_generation_interval)
+			sleep_ms(m_generation_interval);
+		ScopeProfiler sp(g_profiler, "Client: Mesh making");
+
+		MapBlockMesh *mesh_new = new MapBlockMesh(q->data, m_camera_offset);
+
+		MeshUpdateResult r;
+		r.p = q->p;
+		r.mesh = mesh_new;
+		r.ack_block_to_server = q->ack_block_to_server;
+
+		m_queue_out.push_back(r);
+
+		delete q;
+	}
+}
diff --git a/src/mesh_generator_thread.h b/src/mesh_generator_thread.h
new file mode 100644
index 000000000..e74861862
--- /dev/null
+++ b/src/mesh_generator_thread.h
@@ -0,0 +1,135 @@
+/*
+Minetest
+Copyright (C) 2013, 2017 celeron55, Perttu Ahola <celeron55@gmail.com>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser 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.
+*/
+
+#ifndef MESH_GENERATOR_THREAD_HEADER
+#define MESH_GENERATOR_THREAD_HEADER
+
+#include "mapblock_mesh.h"
+#include "threading/mutex_auto_lock.h"
+#include "util/thread.h"
+
+struct CachedMapBlockData
+{
+	v3s16 p;
+	MapNode *data; // A copy of the MapBlock's data member
+	int refcount_from_queue;
+	int last_used_timestamp;
+
+	CachedMapBlockData();
+	~CachedMapBlockData();
+};
+
+struct QueuedMeshUpdate
+{
+	v3s16 p;
+	bool ack_block_to_server;
+	bool urgent;
+	int crack_level;
+	v3s16 crack_pos;
+	MeshMakeData *data; // This is generated in MeshUpdateQueue::pop()
+
+	QueuedMeshUpdate();
+	~QueuedMeshUpdate();
+};
+
+/*
+	A thread-safe queue of mesh update tasks and a cache of MapBlock data
+*/
+class MeshUpdateQueue
+{
+	enum UpdateMode {
+		FORCE_UPDATE,
+		SKIP_UPDATE_IF_ALREADY_CACHED,
+	};
+public:
+	MeshUpdateQueue(Client *client);
+
+	~MeshUpdateQueue();
+
+	// Caches the block at p and its neighbors (if needed) and queues a mesh
+	// update for the block at p
+	void addBlock(Map *map, v3s16 p, bool ack_block_to_server, bool urgent);
+
+	// Returned pointer must be deleted
+	// Returns NULL if queue is empty
+	QueuedMeshUpdate * pop();
+
+	u32 size()
+	{
+		MutexAutoLock lock(m_mutex);
+		return m_queue.size();
+	}
+
+private:
+	Client *m_client;
+	std::vector<QueuedMeshUpdate*> m_queue;
+	std::set<v3s16> m_urgents;
+	std::map<v3s16, CachedMapBlockData*> m_cache;
+	Mutex m_mutex;
+
+	// TODO: Add callback to update these when g_settings changes
+	bool m_cache_enable_shaders;
+	bool m_cache_use_tangent_vertices;
+	bool m_cache_smooth_lighting;
+	int m_meshgen_block_cache_size;
+
+	CachedMapBlockData* cacheBlock(Map *map, v3s16 p, UpdateMode mode,
+			size_t *cache_hit_counter=NULL);
+	CachedMapBlockData* getCachedBlock(const v3s16 &p);
+	void fillDataFromMapBlockCache(QueuedMeshUpdate *q);
+	void cleanupCache();
+};
+
+struct MeshUpdateResult
+{
+	v3s16 p;
+	MapBlockMesh *mesh;
+	bool ack_block_to_server;
+
+	MeshUpdateResult():
+		p(-1338,-1338,-1338),
+		mesh(NULL),
+		ack_block_to_server(false)
+	{
+	}
+};
+
+class MeshUpdateThread : public UpdateThread
+{
+public:
+	MeshUpdateThread(Client *client);
+
+	// Caches the block at p and its neighbors (if needed) and queues a mesh
+	// update for the block at p
+	void updateBlock(Map *map, v3s16 p, bool ack_block_to_server, bool urgent);
+
+	v3s16 m_camera_offset;
+	MutexedQueue<MeshUpdateResult> m_queue_out;
+
+private:
+	MeshUpdateQueue m_queue_in;
+
+	// TODO: Add callback to update these when g_settings changes
+	int m_generation_interval;
+
+protected:
+	virtual void doUpdate();
+};
+
+#endif