From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Thu, 2 Mar 2023 23:19:04 -0800
Subject: [PATCH] Cache whether region files do not exist

The repeated I/O of creating the directory for the regionfile
or for checking if the file exists can be heavy in
when pushing chunk generation extremely hard - as each chunk gen
request may effectively go through to the I/O thread.

diff --git a/src/main/java/io/papermc/paper/chunk/system/io/RegionFileIOThread.java b/src/main/java/io/papermc/paper/chunk/system/io/RegionFileIOThread.java
index a08cde4eefe879adcee7c4118bc38f98c5097ed0..8a11e10b01fa012b2f98b1c193c53251e848f909 100644
--- a/src/main/java/io/papermc/paper/chunk/system/io/RegionFileIOThread.java
+++ b/src/main/java/io/papermc/paper/chunk/system/io/RegionFileIOThread.java
@@ -819,8 +819,14 @@ public final class RegionFileIOThread extends PrioritisedQueueExecutorThread {
                 return file.hasChunk(chunkPos) ? Boolean.TRUE : Boolean.FALSE;
             });
         } else {
+            // first check if the region file for sure does not exist
+            if (taskController.doesRegionFileNotExist(chunkX, chunkZ)) {
+                return Boolean.FALSE;
+            } // else: it either exists or is not known, fall back to checking the loaded region file
+
             return taskController.computeForRegionFileIfLoaded(chunkX, chunkZ, (final RegionFile file) -> {
                 if (file == null) { // null if not loaded
+                    // not sure at this point, let the I/O thread figure it out
                     return Boolean.TRUE;
                 }
 
@@ -1116,6 +1122,10 @@ public final class RegionFileIOThread extends PrioritisedQueueExecutorThread {
             return !this.tasks.isEmpty();
         }
 
+        public boolean doesRegionFileNotExist(final int chunkX, final int chunkZ) {
+            return this.getCache().doesRegionFileNotExistNoIO(new ChunkPos(chunkX, chunkZ));
+        }
+
         public <T> T computeForRegionFile(final int chunkX, final int chunkZ, final boolean existingOnly, final Function<RegionFile, T> function) {
             final RegionFileStorage cache = this.getCache();
             final RegionFile regionFile;
diff --git a/src/main/java/net/minecraft/world/level/chunk/storage/RegionFileStorage.java b/src/main/java/net/minecraft/world/level/chunk/storage/RegionFileStorage.java
index bd502ca721de0cab438d995efa00ad0554c0d2fe..9633b01d2d961fd1403e353484d336376ef009eb 100644
--- a/src/main/java/net/minecraft/world/level/chunk/storage/RegionFileStorage.java
+++ b/src/main/java/net/minecraft/world/level/chunk/storage/RegionFileStorage.java
@@ -28,6 +28,35 @@ public class RegionFileStorage implements AutoCloseable {
 
     private final boolean isChunkData; // Paper
 
+    // Paper start - cache regionfile does not exist state
+    static final int MAX_NON_EXISTING_CACHE = 1024 * 64;
+    private final it.unimi.dsi.fastutil.longs.LongLinkedOpenHashSet nonExistingRegionFiles = new it.unimi.dsi.fastutil.longs.LongLinkedOpenHashSet();
+    private synchronized boolean doesRegionFilePossiblyExist(long position) {
+        if (this.nonExistingRegionFiles.contains(position)) {
+            this.nonExistingRegionFiles.addAndMoveToFirst(position);
+            return false;
+        }
+        return true;
+    }
+
+    private synchronized void createRegionFile(long position) {
+        this.nonExistingRegionFiles.remove(position);
+    }
+
+    private synchronized void markNonExisting(long position) {
+        if (this.nonExistingRegionFiles.addAndMoveToFirst(position)) {
+            while (this.nonExistingRegionFiles.size() >= MAX_NON_EXISTING_CACHE) {
+                this.nonExistingRegionFiles.removeLastLong();
+            }
+        }
+    }
+
+    public synchronized boolean doesRegionFileNotExistNoIO(ChunkPos pos) {
+        long key = ChunkPos.asLong(pos.getRegionX(), pos.getRegionZ());
+        return !this.doesRegionFilePossiblyExist(key);
+    }
+    // Paper end - cache regionfile does not exist state
+
     protected RegionFileStorage(Path directory, boolean dsync) { // Paper - protected constructor
         // Paper start - add isChunkData param
         this(directory, dsync, false);
@@ -77,7 +106,7 @@ public class RegionFileStorage implements AutoCloseable {
     }
     public synchronized RegionFile getRegionFile(ChunkPos chunkcoordintpair, boolean existingOnly, boolean lock) throws IOException {
         // Paper end
-        long i = ChunkPos.asLong(chunkcoordintpair.getRegionX(), chunkcoordintpair.getRegionZ());
+        long i = ChunkPos.asLong(chunkcoordintpair.getRegionX(), chunkcoordintpair.getRegionZ()); final long regionPos = i; // Paper - OBFHELPER
         RegionFile regionfile = (RegionFile) this.regionCache.getAndMoveToFirst(i);
 
         if (regionfile != null) {
@@ -89,15 +118,27 @@ public class RegionFileStorage implements AutoCloseable {
             // Paper end
             return regionfile;
         } else {
+            // Paper start - cache regionfile does not exist state
+            if (existingOnly && !this.doesRegionFilePossiblyExist(regionPos)) {
+                return null;
+            }
+            // Paper end - cache regionfile does not exist state
             if (this.regionCache.size() >= io.papermc.paper.configuration.GlobalConfiguration.get().misc.regionFileCacheSize) { // Paper - configurable
                 ((RegionFile) this.regionCache.removeLast()).close();
             }
 
-            FileUtil.createDirectoriesSafe(this.folder);
+            // Paper - only create directory if not existing only - moved down
             Path path = this.folder;
             int j = chunkcoordintpair.getRegionX();
             Path path1 = path.resolve("r." + j + "." + chunkcoordintpair.getRegionZ() + ".mca"); // Paper - diff on change
-            if (existingOnly && !java.nio.file.Files.exists(path1)) return null; // CraftBukkit
+            if (existingOnly && !java.nio.file.Files.exists(path1)) { // Paper start - cache regionfile does not exist state
+                this.markNonExisting(regionPos);
+                return null; // CraftBukkit
+            } else {
+                this.createRegionFile(regionPos);
+            }
+            // Paper end - cache regionfile does not exist state
+            FileUtil.createDirectoriesSafe(this.folder); // Paper - only create directory if not existing only - moved from above
             RegionFile regionfile1 = new RegionFile(path1, this.folder, this.sync, this.isChunkData); // Paper - allow for chunk regionfiles to regen header
 
             this.regionCache.putAndMoveToFirst(i, regionfile1);