SPIGOT-2634: Concurrency issue in FileIOThread

By: md_5 <git@md-5.net>

paper-server/nms-patches/ChunkRegionLoader.patch

@@ -90,7 +90,38 @@
              }
          }
      }
-@@ -131,10 +179,14 @@
+@@ -98,20 +146,27 @@
+     }
+ 
+     public boolean c() {
+-        if (this.b.isEmpty()) {
++        // CraftBukkit start
++        Iterator<Map.Entry<ChunkCoordIntPair, NBTTagCompound>> iter = this.b.entrySet().iterator();
++        if (!iter.hasNext()) {
++            // CraftBukkit end
+             if (this.f) {
+                 ChunkRegionLoader.a.info("ThreadedAnvilChunkStorage ({}): All chunks are saved", new Object[] { this.d.getName()});
+             }
+ 
+             return false;
+         } else {
+-            ChunkCoordIntPair chunkcoordintpair = (ChunkCoordIntPair) this.b.keySet().iterator().next();
++            // CraftBukkit start
++            Map.Entry<ChunkCoordIntPair, NBTTagCompound> entry = iter.next();
++            iter.remove(); // Pop single entry
++            ChunkCoordIntPair chunkcoordintpair = entry.getKey();
++            // CraftBukkit end
+ 
+             boolean flag;
+ 
+             try {
+                 this.c.add(chunkcoordintpair);
+-                NBTTagCompound nbttagcompound = (NBTTagCompound) this.b.remove(chunkcoordintpair);
++                NBTTagCompound nbttagcompound = (NBTTagCompound) entry.getValue(); // CraftBukkit
+ 
+                 if (nbttagcompound != null) {
+                     try {
+@@ -131,10 +186,14 @@
      }
  
      private void b(ChunkCoordIntPair chunkcoordintpair, NBTTagCompound nbttagcompound) throws IOException {
@@ -106,7 +137,7 @@
      }
  
      public void b(World world, Chunk chunk) throws IOException {}
-@@ -149,6 +201,7 @@
+@@ -149,6 +208,7 @@
                  if (this.c()) {
                      continue;
                  }
@@ -114,7 +145,7 @@
              }
          } finally {
              this.f = false;
-@@ -326,6 +379,13 @@
+@@ -326,6 +386,13 @@
              chunk.a(nbttagcompound.getByteArray("Biomes"));
          }
  
@@ -128,7 +159,7 @@
          NBTTagList nbttaglist1 = nbttagcompound.getList("Entities", 10);
  
          if (nbttaglist1 != null) {
-@@ -369,7 +429,7 @@
+@@ -369,7 +436,7 @@
              }
          }
  
@@ -137,7 +168,7 @@
      }
  
      @Nullable
-@@ -397,14 +457,20 @@
+@@ -397,14 +464,20 @@
      }
  
      @Nullable
@@ -159,7 +190,7 @@
                  return null;
              } else {
                  if (nbttagcompound.hasKeyOfType("Passengers", 9)) {
-@@ -433,8 +499,14 @@
+@@ -433,8 +506,14 @@
          }
      }