Get rid of global buffer that would ruin concurrent MapBlock serialization

diff --git a/src/mapblock.cpp b/src/mapblock.cpp
index e3a6caa199616f6e416e1dc2c044dea12e1a0c17..2bbc0ebbf9f76d9ab0750afb7d24f2caf5920a1b 100644 (file)
--- a/src/mapblock.cpp
+++ b/src/mapblock.cpp
@@ -221,33 +221,36 @@ void MapBlock::expireDayNightDiff()
 /*
        Serialization
 */
+
 // List relevant id-name pairs for ids in the block using nodedef
-// Renumbers the content IDs (starting at 0 and incrementing
-// use static memory requires about 65535 * sizeof(int) ram in order to be
-// sure we can handle all content ids. But it's absolutely worth it as it's
-// a speedup of 4 for one of the major time consuming functions on storing
-// mapblocks.
-static content_t getBlockNodeIdMapping_mapping[USHRT_MAX + 1];
+// Renumbers the content IDs (starting at 0 and incrementing)
 static void getBlockNodeIdMapping(NameIdMapping *nimap, MapNode *nodes,
        const NodeDefManager *nodedef)
 {
-       memset(getBlockNodeIdMapping_mapping, 0xFF, (USHRT_MAX + 1) * sizeof(content_t));
-
-       std::set<content_t> unknown_contents;
+       // The static memory requires about 65535 * sizeof(int) RAM in order to be
+       // sure we can handle all content ids. But it's absolutely worth it as it's
+       // a speedup of 4 for one of the major time consuming functions on storing
+       // mapblocks.
+       thread_local std::unique_ptr<content_t[]> mapping;
+       static_assert(sizeof(content_t) == 2, "content_t must be 16-bit");
+       if (!mapping)
+               mapping = std::make_unique<content_t[]>(USHRT_MAX + 1);
+
+       memset(mapping.get(), 0xFF, (USHRT_MAX + 1) * sizeof(content_t));
+
+       std::unordered_set<content_t> unknown_contents;
        content_t id_counter = 0;
        for (u32 i = 0; i < MapBlock::nodecount; i++) {
                content_t global_id = nodes[i].getContent();
                content_t id = CONTENT_IGNORE;
 
                // Try to find an existing mapping
-               if (getBlockNodeIdMapping_mapping[global_id] != 0xFFFF) {
-                       id = getBlockNodeIdMapping_mapping[global_id];
-               }
-               else
-               {
+               if (mapping[global_id] != 0xFFFF) {
+                       id = mapping[global_id];
+               } else {
                        // We have to assign a new mapping
                        id = id_counter++;
-                       getBlockNodeIdMapping_mapping[global_id] = id;
+                       mapping[global_id] = id;
 
                        const ContentFeatures &f = nodedef->get(global_id);
                        const std::string &name = f.name;
@@ -265,6 +268,7 @@ static void getBlockNodeIdMapping(NameIdMapping *nimap, MapNode *nodes,
                                << "Name for node id " << unknown_content << " not known" << std::endl;
        }
 }
+
 // Correct ids in the block to match nodedef based on names.
 // Unknown ones are added to nodedef.
 // Will not update itself to match id-name pairs in nodedef.