From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Tue, 23 Oct 2018 23:14:38 -0400
Subject: [PATCH] Improve Server Thread Pool and Thread Priorities

Use a simple executor since Fork join is a much more complex pool
type and we are not using its capabilities.

Set thread priorities so main thread has above normal priority over
server threads

Allow usage of a single thread executor by not using ForkJoin so single core CPU's
and reduce worldgen thread worker count for low core count CPUs.

== AT ==
public net.minecraft.Util onThreadException(Ljava/lang/Thread;Ljava/lang/Throwable;)V

Co-authored-by: Spottedleaf <Spottedleaf@users.noreply.github.com>

diff --git a/src/main/java/io/papermc/paper/util/ServerWorkerThread.java b/src/main/java/io/papermc/paper/util/ServerWorkerThread.java
new file mode 100644
index 0000000000000000000000000000000000000000..b60f59cf5cc8eb84a6055b7861857dece7f2501b
--- /dev/null
+++ b/src/main/java/io/papermc/paper/util/ServerWorkerThread.java
@@ -0,0 +1,14 @@
+package io.papermc.paper.util;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import net.minecraft.Util;
+
+public class ServerWorkerThread extends Thread {
+    private static final AtomicInteger threadId = new AtomicInteger(1);
+    public ServerWorkerThread(Runnable target, String poolName, int prioritityModifier) {
+        super(target, "Worker-" + poolName + "-" + threadId.getAndIncrement());
+        setPriority(Thread.NORM_PRIORITY+prioritityModifier); // Deprioritize over main
+        this.setDaemon(true);
+        this.setUncaughtExceptionHandler(Util::onThreadException);
+    }
+}
diff --git a/src/main/java/net/minecraft/Util.java b/src/main/java/net/minecraft/Util.java
index cf54e2c8e8aadb9e7343382a5ba59c657234c9b9..c7a21a11efba5c212958d56095217621828c1062 100644
--- a/src/main/java/net/minecraft/Util.java
+++ b/src/main/java/net/minecraft/Util.java
@@ -90,7 +90,7 @@ public class Util {
     private static final int DEFAULT_MAX_THREADS = 255;
     private static final int DEFAULT_SAFE_FILE_OPERATION_RETRIES = 10;
     private static final String MAX_THREADS_SYSTEM_PROPERTY = "max.bg.threads";
-    private static final ExecutorService BACKGROUND_EXECUTOR = makeExecutor("Main");
+    private static final ExecutorService BACKGROUND_EXECUTOR = makeExecutor("Main", -1); // Paper - Perf: add priority
     private static final ExecutorService IO_POOL = makeIoExecutor("IO-Worker-", false);
     private static final ExecutorService DOWNLOAD_POOL = makeIoExecutor("Download-", true);
     // Paper start - don't submit BLOCKING PROFILE LOOKUPS to the world gen thread
@@ -160,15 +160,27 @@ public class Util {
         return FILENAME_DATE_TIME_FORMATTER.format(ZonedDateTime.now());
     }
 
-    private static ExecutorService makeExecutor(String name) {
-        int i = Mth.clamp(Runtime.getRuntime().availableProcessors() - 1, 1, getMaxThreads());
+    private static ExecutorService makeExecutor(String s, int priorityModifier) { // Paper - Perf: add priority
+        // Paper start - Perf: use simpler thread pool that allows 1 thread and reduce worldgen thread worker count for low core count CPUs
+        int cpus = Runtime.getRuntime().availableProcessors() / 2;
+        int i;
+        if (cpus <= 4) {
+            i = cpus <= 2 ? 1 : 2;
+        } else if (cpus <= 8) {
+            // [5, 8]
+            i = Math.max(3, cpus - 2);
+        } else {
+            i = cpus * 2 / 3;
+        }
+        i = Math.min(8, i);
+        i = Integer.getInteger("Paper.WorkerThreadCount", i);
         ExecutorService executorService;
         if (i <= 0) {
             executorService = MoreExecutors.newDirectExecutorService();
         } else {
-            AtomicInteger atomicInteger = new AtomicInteger(1);
-            executorService = new ForkJoinPool(i, pool -> {
-                ForkJoinWorkerThread forkJoinWorkerThread = new ForkJoinWorkerThread(pool) {
+            executorService = new java.util.concurrent.ThreadPoolExecutor(i, i,0L, TimeUnit.MILLISECONDS, new java.util.concurrent.LinkedBlockingQueue<>(), target -> new io.papermc.paper.util.ServerWorkerThread(target, s, priorityModifier));
+        }
+        /*
                     @Override
                     protected void onTermination(Throwable throwable) {
                         if (throwable != null) {
@@ -184,6 +196,7 @@ public class Util {
                 return forkJoinWorkerThread;
             }, Util::onThreadException, true);
         }
+        }*/ // Paper end - Perf: use simpler thread pool
 
         return executorService;
     }
diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index a8a53b0aad6cda7fa1cd0565b5a4249a228f87f7..015eb2e8e9bf28435a8ea9aff544bcd95e679bde 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -316,6 +316,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
         thread.setUncaughtExceptionHandler((thread1, throwable) -> {
             MinecraftServer.LOGGER.error("Uncaught exception in server thread", throwable);
         });
+        thread.setPriority(Thread.NORM_PRIORITY+2); // Paper - Perf: Boost priority
         if (Runtime.getRuntime().availableProcessors() > 4) {
             thread.setPriority(8);
         }