PaperMC/Spigot-Server-Patches/0374-Fix-FileIOThread-concurrency-issues.patch

From d5f43cbf4f3216b3bdc8f527937ed13f4ce5bbe6 Mon Sep 17 00:00:00 2001
From: Shane Freeder <theboyetronic@gmail.com>
Date: Wed, 3 Oct 2018 19:04:53 +0100
Subject: [PATCH] Fix FileIOThread concurrency issues

FileIOThread was using two volatile counters in order to track if
any pending work was in the queue, this causes potential concurrency
issues when this counter is updated from multiple threads, potentially
causing these counters to desync due to the unsafe volatile update

diff --git a/src/main/java/net/minecraft/server/FileIOThread.java b/src/main/java/net/minecraft/server/FileIOThread.java
index 3c688f546..570624600 100644
--- a/src/main/java/net/minecraft/server/FileIOThread.java
+++ b/src/main/java/net/minecraft/server/FileIOThread.java
@@ -10,7 +10,7 @@ public class FileIOThread implements Runnable {
 
     private static final Logger a = LogManager.getLogger();
     private static final FileIOThread b = new FileIOThread();
-    private final List<IAsyncChunkSaver> c = Collections.synchronizedList(Lists.newArrayList());
+    private final List<IAsyncChunkSaver> c = Collections.synchronizedList(Lists.newArrayList()); private List<IAsyncChunkSaver> getThreadedIOQueue() { return c; } // Paper - OBFHELPER
     private volatile long d;
     private volatile long e;
     private volatile boolean f;
@@ -75,7 +75,7 @@ public class FileIOThread implements Runnable {
     public void b() throws InterruptedException {
         this.f = true;
 
-        while (this.d != this.e) {
+        while(!this.getThreadedIOQueue().isEmpty()) { // Paper - check actual list size
             Thread.sleep(10L);
         }
 
-- 
2.20.1