From e75ec71b32d061b44fceff76549f7158276c2847 Mon Sep 17 00:00:00 2001
From: Andrew Steinborn <git@steinborn.me>
Date: Mon, 17 Sep 2018 01:03:07 -0400
Subject: [PATCH] Improve native initialization logic

This uses the double-check pattern as recommended in Effective Java.
---
 .../natives/util/NativeCodeLoader.java        | 27 ++++++++++++-------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/native/src/main/java/com/velocitypowered/natives/util/NativeCodeLoader.java b/native/src/main/java/com/velocitypowered/natives/util/NativeCodeLoader.java
index 2f07378c8..692df5375 100644
--- a/native/src/main/java/com/velocitypowered/natives/util/NativeCodeLoader.java
+++ b/native/src/main/java/com/velocitypowered/natives/util/NativeCodeLoader.java
@@ -8,7 +8,7 @@ import java.util.function.Supplier;
 
 public class NativeCodeLoader<T> implements Supplier<T> {
     private final List<Variant<T>> variants;
-    private Variant<T> selected;
+    private volatile Variant<T> selected;
 
     public NativeCodeLoader(List<Variant<T>> variants) {
         this.variants = ImmutableList.copyOf(variants);
@@ -17,25 +17,32 @@ public class NativeCodeLoader<T> implements Supplier<T> {
     @Override
     public T get() {
         if (selected == null) {
-            selected = select();
+            selected = tryLoad();
         }
         return selected.object;
     }
 
-    private Variant<T> select() {
-        for (Variant<T> variant : variants) {
-            T got = variant.get();
-            if (got == null) {
-                continue;
+    private Variant<T> tryLoad() {
+        synchronized (this) {
+            if (selected != null) {
+                return selected;
             }
-            return variant;
+
+            for (Variant<T> variant : variants) {
+                T got = variant.get();
+                if (got == null) {
+                    continue;
+                }
+                selected = variant;
+                return selected;
+            }
+            throw new IllegalArgumentException("Can't find any suitable variants");
         }
-        throw new IllegalArgumentException("Can't find any suitable variants");
     }
 
     public String getLoadedVariant() {
         if (selected == null) {
-            selected = select();
+            selected = tryLoad();
         }
         return selected.name;
     }