From c0e20a6fe5ec610f7ee0d9c4022ef01030792216 Mon Sep 17 00:00:00 2001
From: Jordan <dordsor21@gmail.com>
Date: Mon, 10 Jul 2023 22:16:05 +0100
Subject: [PATCH] feat: provide some information upon
 OverlappingFileLockException (#2341)

---
 .../clipboard/DiskOptimizedClipboard.java     | 36 ++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/worldedit-core/src/main/java/com/fastasyncworldedit/core/extent/clipboard/DiskOptimizedClipboard.java b/worldedit-core/src/main/java/com/fastasyncworldedit/core/extent/clipboard/DiskOptimizedClipboard.java
index a9704e36b..3f7c746c3 100644
--- a/worldedit-core/src/main/java/com/fastasyncworldedit/core/extent/clipboard/DiskOptimizedClipboard.java
+++ b/worldedit-core/src/main/java/com/fastasyncworldedit/core/extent/clipboard/DiskOptimizedClipboard.java
@@ -39,6 +39,8 @@ import java.net.URI;
 import java.nio.ByteBuffer;
 import java.nio.MappedByteBuffer;
 import java.nio.channels.FileChannel;
+import java.nio.channels.FileLock;
+import java.nio.channels.OverlappingFileLockException;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
@@ -46,6 +48,7 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
 
 /**
  * A clipboard with disk backed storage. (lower memory + loads on crash)
@@ -59,6 +62,7 @@ public class DiskOptimizedClipboard extends LinearClipboard {
     private static final int HEADER_SIZE = 27; // Current header size
     private static final int VERSION_1_HEADER_SIZE = 22; // Header size of "version 1"
     private static final int VERSION_2_HEADER_SIZE = 27; // Header size of "version 2" i.e. when NBT/entities could be saved
+    private static final Map<String, LockHolder> LOCK_HOLDER_CACHE = new ConcurrentHashMap<>();
 
     private final HashMap<IntTriple, CompoundTag> nbtMap;
     private final File file;
@@ -301,7 +305,23 @@ public class DiskOptimizedClipboard extends LinearClipboard {
     private void init() throws IOException {
         if (this.fileChannel == null) {
             this.fileChannel = braf.getChannel();
-            this.fileChannel.lock();
+            try {
+                FileLock lock = this.fileChannel.lock();
+                LOCK_HOLDER_CACHE.put(file.getName(), new LockHolder(lock));
+            } catch (OverlappingFileLockException e) {
+                LockHolder existing = LOCK_HOLDER_CACHE.get(file.getName());
+                if (existing != null) {
+                    long ms = System.currentTimeMillis() - existing.lockHeldSince;
+                    LOGGER.error(
+                            "Cannot lock clipboard file {} acquired by thread {}, {}ms ago",
+                            file.getName(),
+                            existing.thread,
+                            ms
+                    );
+                }
+                // Rethrow to prevent clipboard access
+                throw e;
+            }
             this.byteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, braf.length());
         }
     }
@@ -737,4 +757,18 @@ public class DiskOptimizedClipboard extends LinearClipboard {
         return false;
     }
 
+    private static class LockHolder {
+
+        final FileLock lock;
+        final long lockHeldSince;
+        final String thread;
+
+        LockHolder(FileLock lock) {
+            this.lock = lock;
+            lockHeldSince = System.currentTimeMillis();
+            this.thread = Thread.currentThread().getName();
+        }
+    }
+
+
 }