Reduce lock scope in FSDirectory.DeleteFile, apache#1428 (apache#1429)

Author: marionoack

src/Lucene.Net/Store/FSDirectory.cs

@@ -317,31 +317,37 @@ public override void DeleteFile(string name)
             EnsureOpen();
             string file = Path.Combine(m_directory.FullName, name);
 
-            // LUCENENET Specific: See remarks for m_staleFiles field.
-            UninterruptableMonitor.Enter(m_syncLock);
-            try
+            // LUCENENET specific: We need to explicitly throw when the file has already been deleted,
+            // since FileInfo doesn't do that for us.
+            // (An enhancement carried over from Lucene 8.2.0)
+            if (!File.Exists(file))
             {
-                // LUCENENET specific: We need to explicitly throw when the file has already been deleted,
-                // since FileInfo doesn't do that for us.
-                // (An enhancement carried over from Lucene 8.2.0)
-                if (!File.Exists(file))
-                {
-                    throw new FileNotFoundException("Cannot delete " + file + " because it doesn't exist.");
-                }
+                throw new FileNotFoundException("Cannot delete " + file + " because it doesn't exist.");
+            }
 
-                try
-                {
-                    File.Delete(file);
-                    if (File.Exists(file))
-                    {
-                        throw new IOException("Cannot delete " + file);
-                    }
-                }
-                catch (Exception e)
+            // LUCENENET NOTE: Do NOT hold m_syncLock while deleting. On a network share (SMB),
+            // File.Delete can block for a long time (e.g. waiting for the server to break an
+            // oplock/lease on a file this client still has open). Holding m_syncLock here would
+            // block every concurrent Sync() and IndexOutput.Dispose() on this directory behind
+            // a single stalled delete, freezing the whole writer. Only the m_staleFiles
+            // bookkeeping below needs the lock (see remarks for the m_staleFiles field);
+            // upstream Java likewise performs the delete without any directory-wide lock.
+            try
+            {
+                File.Delete(file);
+                if (File.Exists(file))
                 {
-                    throw new IOException("Cannot delete " + file, e);
+                    throw new IOException("Cannot delete " + file);
                 }
+            }
+            catch (Exception e)
+            {
+                throw new IOException("Cannot delete " + file, e);
+            }
 
+            UninterruptableMonitor.Enter(m_syncLock);
+            try
+            {
                 m_staleFiles.Remove(name);
             }
             finally