Prevent MapBlocks in generation from being unloaded (#16339)

This change prevents issues arising from partial generation of MapChunks, which are liable to be regenerated completely when ungenerated MapBlocks within are encountered.

Co-authored-by: Po Lu <luangruo@yahoo.com>
Co-authored-by: sfan5 <sfan5@live.de>

src/emerge.cpp

@@ -737,6 +737,8 @@ void *EmergeThread::run()
 
 			if (!error)
 				block = finishGen(pos, &bmdata, &modified_blocks);
+			else
+				m_map->cancelBlockMake(&bmdata);
 			if (!block || error)
 				action = EMERGE_ERRORED;
 

src/servermap.cpp

@@ -201,8 +201,8 @@ bool ServerMap::initBlockMake(v3s16 blockpos, BlockMakeData *data)
 {
 	assert(data);
 	s16 csize = getMapgenParams()->chunksize;
-	v3s16 bpmin = EmergeManager::getContainingChunk(blockpos, csize);
+	const v3s16 bpmin = EmergeManager::getContainingChunk(blockpos, csize);
-	v3s16 bpmax = bpmin + v3s16(1, 1, 1) * (csize - 1);
+	const v3s16 bpmax = bpmin + v3s16(1, 1, 1) * (csize - 1);
 
 	if (!m_chunks_in_progress.insert(bpmin).second)
 		return false;
@@ -210,11 +210,10 @@ bool ServerMap::initBlockMake(v3s16 blockpos, BlockMakeData *data)
 	bool enable_mapgen_debug_info = m_emerge->enable_mapgen_debug_info;
 	EMERGE_DBG_OUT("initBlockMake(): " << bpmin << " - " << bpmax);
 
-	v3s16 extra_borders(1, 1, 1);
+	const v3s16 full_bpmin = bpmin - EMERGE_EXTRA_BORDER;
-	v3s16 full_bpmin = bpmin - extra_borders;
+	const v3s16 full_bpmax = bpmax + EMERGE_EXTRA_BORDER;
-	v3s16 full_bpmax = bpmax + extra_borders;
 
-	// Do nothing if not inside mapgen limits (+-1 because of neighbors)
+	// Do nothing if not fully inside mapgen limits
 	if (blockpos_over_mapgen_limit(full_bpmin) ||
 			blockpos_over_mapgen_limit(full_bpmax))
 		return false;
@@ -246,6 +245,7 @@ bool ServerMap::initBlockMake(v3s16 blockpos, BlockMakeData *data)
 				bool ug = m_emerge->isBlockUnderground(p);
 				block->setIsUnderground(ug);
 			}
+			block->refGrab();
 		}
 	}
 
@@ -263,13 +263,28 @@ bool ServerMap::initBlockMake(v3s16 blockpos, BlockMakeData *data)
 	return true;
 }
 
+void ServerMap::cancelBlockMake(BlockMakeData *data)
+{
+	assert(data->vmanip); // no vmanip = initBlockMake did not complete (caller mistake)
+
+	const v3s16 full_bpmin = data->blockpos_min - EMERGE_EXTRA_BORDER;
+	const v3s16 full_bpmax = data->blockpos_max + EMERGE_EXTRA_BORDER;
+	for (s16 x = full_bpmin.X; x <= full_bpmax.X; x++)
+	for (s16 z = full_bpmin.Z; z <= full_bpmax.Z; z++)
+	for (s16 y = full_bpmin.Y; y <= full_bpmax.Y; y++) {
+		MapBlock *block = getBlockNoCreateNoEx(v3s16(x, y, z));
+		if (block)
+			block->refDrop();
+	}
+}
+
 void ServerMap::finishBlockMake(BlockMakeData *data,
 	std::map<v3s16, MapBlock*> *changed_blocks, u32 now)
 {
 	assert(data);
 	assert(changed_blocks);
-	v3s16 bpmin = data->blockpos_min;
+	const v3s16 bpmin = data->blockpos_min;
-	v3s16 bpmax = data->blockpos_max;
+	const v3s16 bpmax = data->blockpos_max;
 
 	bool enable_mapgen_debug_info = m_emerge->enable_mapgen_debug_info;
 	EMERGE_DBG_OUT("finishBlockMake(): " << bpmin << " - " << bpmax);
@@ -306,18 +321,31 @@ void ServerMap::finishBlockMake(BlockMakeData *data,
 			MOD_REASON_EXPIRE_IS_AIR);
 	}
 
-	// Note: this does not apply to the extra border area
+	const v3s16 full_bpmin = bpmin - EMERGE_EXTRA_BORDER;
-	for (s16 x = bpmin.X; x <= bpmax.X; x++)
+	const v3s16 full_bpmax = bpmax + EMERGE_EXTRA_BORDER;
-	for (s16 z = bpmin.Z; z <= bpmax.Z; z++)
-	for (s16 y = bpmin.Y; y <= bpmax.Y; y++) {
-		MapBlock *block = getBlockNoCreateNoEx(v3s16(x, y, z));
-		if (!block)
-			continue;
 
+	v3s16 bp;
+	for (bp.X = full_bpmin.X; bp.X <= full_bpmax.X; bp.X++)
+	for (bp.Z = full_bpmin.Z; bp.Z <= full_bpmax.Z; bp.Z++)
+	for (bp.Y = full_bpmin.Y; bp.Y <= full_bpmax.Y; bp.Y++) {
+		MapBlock *block = getBlockNoCreateNoEx(bp);
+		if (!block) {
+			warningstream << "ServerMap::finishBlockMake: block " << bp
+				<< " disappeared during generation" << std::endl;
+			continue;
+		}
+
+		block->refDrop();
+
+		/* Border blocks are grabbed during
+		   generation but mustn't be marked generated. */
+		if (bp >= bpmin && bp <= bpmax) {
 			block->setGenerated(true);
-		// Set timestamp to ensure correct application of LBMs and other stuff
+			// Set timestamp to ensure correct application
+			// of LBMs and other stuff.
 			block->setTimestampNoChangedFlag(now);
 		}
+	}
 
 	m_chunks_in_progress.erase(bpmin);
 }

src/servermap.h

@@ -67,6 +67,7 @@ public:
 	/// @param now current game time
 	void finishBlockMake(BlockMakeData *data,
 		std::map<v3s16, MapBlock*> *changed_blocks, u32 now);
+	void cancelBlockMake(BlockMakeData *data);
 
 	/*
 		Get a block from somewhere.
@@ -169,6 +170,9 @@ protected:
 private:
 	friend class ModApiMapgen; // for m_transforming_liquid
 
+	// extra border area during mapgen (in blocks)
+	constexpr static v3s16 EMERGE_EXTRA_BORDER{1, 1, 1};
+
 	// Emerge manager
 	EmergeManager *m_emerge;