PaperMC/Spigot-Server-Patches/Chunk-save-queue-improvements.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Fri, 4 Mar 2016 18:18:37 -0600
Subject: [PATCH] Chunk save queue improvements

For some unknown reason, Minecraft is sleeping 10ms between every single chunk being saved to disk.
Under high chunk load/unload activity (lots of movement / teleporting), this causes the chunk unload queue
to build up in size.

This has multiple impacts:
1) Performance of the unload queue itself - The save thread is pretty ineffecient for how it accesses it
   By letting the queue get larger, checking and popping work off the queue can get less performant.
2) Performance of chunk loading - As with #1, chunk loads also have to check this queue when loading
   chunk data so that it doesn't load stale data if new data is pending write to disk.
3) Memory Usage - The entire chunk has been serialized to NBT, and now sits in this queue. This leads to
   elevated memory usage, and then the objects used in the serialization sit around longer than needed,
   resulting in promotion to Old Generation instead of dying young.

To optimize this, we change the entire unload queue to be a proper queue. This improves the behavior of popping
the first queued chunk off, instead of abusing iterators like Mojang was doing.

This also improves reliability of chunk saving, as the previous hack job had a race condition that could
fail to save some chunks.

Then finally, Sleeping will by default be removed, but due to known issues with 1.9, a config option was added.
But if sleeps are to remain enabled, we at least lower the sleep interval so it doesn't have as much negative impact.

diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
index 0d68ffd75a..fd00c320ce 100644
--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
@@ -0,0 +0,0 @@ public class PaperConfig {
     private static void chunkLoadThreads() {
         minChunkLoadThreads = Math.min(6, getInt("settings.min-chunk-load-threads", 2)); // Keep people from doing stupid things with max of 6
     }
+
+    public static boolean enableFileIOThreadSleep;
+    private static void enableFileIOThreadSleep() {
+        enableFileIOThreadSleep = getBoolean("settings.sleep-between-chunk-saves", false);
+        if (enableFileIOThreadSleep) Bukkit.getLogger().info("Enabled sleeping between chunk saves, beware of memory issues");
+    }
 }
diff --git a/src/main/java/net/minecraft/server/ChunkRegionLoader.java b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
index 2e9bd0949a..1dbcedbf94 100644
--- a/src/main/java/net/minecraft/server/ChunkRegionLoader.java
+++ b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
@@ -0,0 +0,0 @@ import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import javax.annotation.Nullable;
+import java.util.concurrent.ConcurrentLinkedQueue; // Paper
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 // Spigot start
@@ -0,0 +0,0 @@ import org.spigotmc.SupplierUtils;
 
 public class ChunkRegionLoader implements IChunkLoader, IAsyncChunkSaver {
 
+    // Paper start - Chunk queue improvements
+    private static class QueuedChunk {
+        public ChunkCoordIntPair coords;
+        public Supplier<NBTTagCompound> compoundSupplier;
+        public Runnable onSave;
+
+        public QueuedChunk(Runnable run) {
+            this.coords = null;
+            this.compoundSupplier = null;
+            this.onSave = run;
+        }
+
+        public QueuedChunk(ChunkCoordIntPair coords, Supplier<NBTTagCompound> compoundSupplier) {
+            this.coords = coords;
+            this.compoundSupplier = compoundSupplier;
+        }
+    }
+    final private ConcurrentLinkedQueue<QueuedChunk> queue = new ConcurrentLinkedQueue<>();
+    // Paper end
+
     private static final Logger a = LogManager.getLogger();
     private final Map<ChunkCoordIntPair, Supplier<NBTTagCompound>> b = java.util.Collections.synchronizedMap(Maps.newHashMap()); // CraftBukkit // Spigot
     private final File c;
@@ -0,0 +0,0 @@ public class ChunkRegionLoader implements IChunkLoader, IAsyncChunkSaver {
                     }
                 };
             }
-
-            this.a(chunkcoordintpair, SupplierUtils.createUnivaluedSupplier(completion, unloaded && this.b.size() < SAVE_QUEUE_TARGET_SIZE));
+            this.a(chunkcoordintpair, SupplierUtils.createUnivaluedSupplier(completion, unloaded)); // Paper - Remove save queue target size
+            // Paper end
             // Spigot end
         } catch (Exception exception) {
             ChunkRegionLoader.a.error("Failed to save chunk", exception);
@@ -0,0 +0,0 @@ public class ChunkRegionLoader implements IChunkLoader, IAsyncChunkSaver {
     }
 
     protected void a(ChunkCoordIntPair chunkcoordintpair, Supplier<NBTTagCompound> nbttagcompound) { // Spigot
-        this.b.put(chunkcoordintpair, nbttagcompound);
+        synchronized (this.b) { // Paper - synchronize while modifying the map
+            queue.add(new QueuedChunk(chunkcoordintpair, nbttagcompound)); // Paper - Chunk queue improvements
+            this.b.put(chunkcoordintpair, nbttagcompound);
+        }
         FileIOThread.a().a(this);
     }
 
@@ -0,0 +0,0 @@ public class ChunkRegionLoader implements IChunkLoader, IAsyncChunkSaver {
     }
 
     private boolean processSaveQueueEntry(boolean logCompletion) {
-        synchronized (this.b) { // CraftBukkit
-        Iterator iterator = this.b.entrySet().iterator();
-        if (!iterator.hasNext()) {
+        // Paper start - Chunk queue improvements
+        QueuedChunk chunk = queue.poll();
+        if (chunk == null) {
+        // Paper - end
             if (logCompletion) { // CraftBukkit
                 ChunkRegionLoader.a.info("ThreadedAnvilChunkStorage ({}): All chunks are saved", this.c.getName());
             }
 
             return false;
         } else {
-            Entry entry = (Entry) iterator.next();
-
-            iterator.remove();
-            ChunkCoordIntPair chunkcoordintpair = (ChunkCoordIntPair) entry.getKey();
-            Supplier<NBTTagCompound> nbttagcompound = (Supplier<NBTTagCompound>) entry.getValue(); // Spigot
+            // Paper start
+            if (chunk.onSave != null) {
+                chunk.onSave.run();
+                return true;
+            }
+            // Paper end
+            ChunkCoordIntPair chunkcoordintpair = chunk.coords; // Paper - Chunk queue improvements
+            Supplier<NBTTagCompound> nbttagcompound = chunk.compoundSupplier; // Spigot // Paper
 
             if (nbttagcompound == null) {
                 return true;
@@ -0,0 +0,0 @@ public class ChunkRegionLoader implements IChunkLoader, IAsyncChunkSaver {
                     // CraftBukkit start
                     RegionFileCache.write(this.c, chunkcoordintpair.x, chunkcoordintpair.z, SupplierUtils.getIfExists(nbttagcompound)); // Spigot
 
+                    // Paper start remove from map only if this was the latest version of the chunk
+                    synchronized (this.b) {
+                        // This will not equal if a newer version is still pending - wait until newest is saved to remove
+                        if (this.b.get(chunkcoordintpair) == chunk.compoundSupplier) {
+                            this.b.remove(chunkcoordintpair);
+                        }
+                    }
+                    // Paper end
                     /*
                     NBTCompressedStreamTools.a(nbttagcompound, (DataOutput) dataoutputstream);
                     dataoutputstream.close();
@@ -0,0 +0,0 @@ public class ChunkRegionLoader implements IChunkLoader, IAsyncChunkSaver {
                 return true;
             }
         }
-        } // CraftBukkit
+        // } // CraftBukkit // Paper
     }
 
     private ChunkStatus.Type a(@Nullable NBTTagCompound nbttagcompound) {
diff --git a/src/main/java/net/minecraft/server/FileIOThread.java b/src/main/java/net/minecraft/server/FileIOThread.java
index a3aba244af..97917551a4 100644
--- a/src/main/java/net/minecraft/server/FileIOThread.java
+++ b/src/main/java/net/minecraft/server/FileIOThread.java
@@ -0,0 +0,0 @@ public class FileIOThread implements Runnable {
         for(int i = 0; i < this.c.size(); ++i) {
             IAsyncChunkSaver iasyncchunksaver = (IAsyncChunkSaver)this.c.get(i);
             boolean flag;
-            synchronized(iasyncchunksaver) {
+            //synchronized(iasyncchunksaver) { // Paper - remove synchronized
                 flag = iasyncchunksaver.a();
-            }
+            //} // Paper
 
             if (!flag) {
                 this.c.remove(i--);
                 ++this.e;
             }
 
+            if (com.destroystokyo.paper.PaperConfig.enableFileIOThreadSleep) { // Paper
             try {
-                Thread.sleep(this.f ? 0L : 10L);
+                Thread.sleep(this.f ? 0L : 1L); // Paper
             } catch (InterruptedException interruptedexception1) {
                 interruptedexception1.printStackTrace();
-            }
+            }} // Paper
         }
 
         if (this.c.isEmpty()) {
--