Multi IO threads w/ fixes default config value

src/main/java/net/minecraft/server/FileIOThread.java

@@ -1,8 +1,11 @@
 package net.minecraft.server;
 
 import com.google.common.collect.Lists;
+
 import java.util.Collections;
 import java.util.List;
+import java.util.concurrent.TimeUnit;
+
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
@@ -14,13 +17,27 @@ public class FileIOThread implements Runnable {
     private volatile long d;
     private volatile long e;
     private volatile boolean f;
+    // Akarin start
+    private final java.util.concurrent.ExecutorService executor = java.util.concurrent.Executors.newFixedThreadPool(io.akarin.server.core.AkarinGlobalConfig.fileIOThreads, new com.google.common.util.concurrent.ThreadFactoryBuilder().setUncaughtExceptionHandler(new ThreadNamedUncaughtExceptionHandler(FileIOThread.a)).setNameFormat("Akarin File IO Thread - %1$d").setPriority(1).build());
+
+    @lombok.SneakyThrows
+    private void writeChunk(IAsyncChunkSaver iasyncchunksaver)  {
+        if (!iasyncchunksaver.a() /* writeNextIO */) { // returns whether the writing was unsuccessful
+            if (com.destroystokyo.paper.PaperConfig.enableFileIOThreadSleep) { // Paper
+                Thread.sleep(this.f ? 0L : 2L); // Paper
+            }
+        } else {
+            writeChunk(iasyncchunksaver);
+        }
+    }
+    // Akarin end
 
     private FileIOThread() {
         Thread thread = new Thread(this, "File IO Thread");
 
         thread.setUncaughtExceptionHandler(new ThreadNamedUncaughtExceptionHandler(FileIOThread.a));
         thread.setPriority(1);
-        thread.start();
+        //thread.start(); // Akarin
     }
 
     public static FileIOThread a() {
@@ -66,10 +83,13 @@ public class FileIOThread implements Runnable {
     }
 
     public void a(IAsyncChunkSaver iasyncchunksaver) {
-        if (!this.c.contains(iasyncchunksaver)) {
-            ++this.d;
-            this.c.add(iasyncchunksaver);
-        }
+        // Akarin start
+        //if (!this.c.contains(iasyncchunksaver)) {
+        //    ++this.d;
+        //    this.c.add(iasyncchunksaver);
+        //}
+        executor.execute(() -> writeChunk(iasyncchunksaver));
+        // Akarin end
     }
 
     public void b() throws InterruptedException {
@@ -78,6 +98,8 @@ public class FileIOThread implements Runnable {
         while(!this.getThreadedIOQueue().isEmpty()) { // Paper - check actual list size
             Thread.sleep(10L);
         }
+        executor.shutdown(); // Akarin
+        executor.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS); // Akarin
 
         this.f = false;
     }