From d435cc4e885c3c821ef1a3f703e56729cd9e436f Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Mon, 4 May 2020 00:38:13 -0400
Subject: [PATCH] Cleanup Region Files Direct Memory on close

Mojang was semi leaking native memory here by relying on finalizers
to clean up the direct memory.

Finalizers have no guarantee on when they will be ran, and since this is
old generation memory, it might be a while before its called.

diff --git a/src/main/java/net/minecraft/server/RegionFile.java b/src/main/java/net/minecraft/server/RegionFile.java
index df728e2c0a..20927d55c6 100644
--- a/src/main/java/net/minecraft/server/RegionFile.java
+++ b/src/main/java/net/minecraft/server/RegionFile.java
@@ -30,7 +30,7 @@ public class RegionFile implements AutoCloseable {
     private final FileChannel dataFile;
     private final java.nio.file.Path d;
     private final RegionFileCompression e;
-    private final ByteBuffer f;
+    private final ByteBuffer f; private ByteBuffer getFileBuffer() { return f; } // Paper - clean up direct buffers on close
     private final IntBuffer g;
     private final IntBuffer h;
     private final RegionFileBitSet freeSectors;
@@ -403,10 +403,59 @@ public class RegionFile implements AutoCloseable {
         }
         } finally { // Paper start - Prevent regionfiles from being closed during use
             this.fileLock.unlock();
+            if (getFileBuffer().isDirect()) cleanDirectByteBuffer(getFileBuffer()); // Paper - clean up direct buffers on close
         }
         } // Paper end
 
     }
+    // Paper start
+    private static int getVersion() {
+        String version = System.getProperty("java.version");
+        if(version.startsWith("1.")) {
+            version = version.substring(2, 3);
+        } else {
+            int dot = version.indexOf(".");
+            if(dot != -1) { version = version.substring(0, dot); }
+        } return Integer.parseInt(version);
+    }
+    static java.lang.reflect.Method unsafeClean;
+    static sun.misc.Unsafe unsafe = com.destroystokyo.paper.utils.UnsafeUtils.getUnsafe();
+    static java.util.function.Consumer<ByteBuffer> cleaner;
+    static {
+        try {
+            if (unsafe != null) {
+                unsafeClean = unsafe.getClass().getMethod("invokeCleaner", ByteBuffer.class);
+                if (unsafeClean != null) {
+                    cleaner = (buf) -> {
+                        try {
+                            unsafeClean.invoke(unsafe, buf);
+                        } catch (Exception ex) {
+                            com.destroystokyo.paper.util.SneakyThrow.sneaky(ex);
+                        }
+                    };
+                    LOGGER.info("[RegionFile] Using Java 9+ invokeCleaner DirectByteBuffer cleanup method");
+                }
+            }
+        } catch (java.lang.NoSuchMethodException e) {}
+        if (cleaner == null && getVersion() <= 8) {
+            cleaner = (buf) -> {
+                ((sun.nio.ch.DirectBuffer) buf).cleaner().clean();
+            };
+            LOGGER.info("[RegionFile] Using Java 8 DirectByteBuffer cleanup method");
+        }
+    }
+    public static void cleanDirectByteBuffer(ByteBuffer toBeDestroyed) {
+        try {
+            if (cleaner != null) {
+                cleaner.accept(toBeDestroyed);
+            }
+        } catch (Exception ex) {
+            LOGGER.warn("Failed automatically cleaning DirectByteBuffer");
+            ex.printStackTrace();
+            cleaner = null;
+        }
+    }
+    // Paper end
 
     private void c() throws IOException {
         int i = (int) this.dataFile.size();
-- 
2.26.0