Fix for Windows file locking (os error 1224)

unsloth_zoo/saving_utils.py

@@ -792,7 +792,82 @@ def _merge_and_overwrite_lora(
                         tensors[key] = resized[key]
                     else:
                         tensors[key] = f.get_tensor(key)
-            save_file(tensors, filename_original)
+
+            # Fix for Windows file locking (os error 1224)
+            # Use retry logic with safe atomic operations
+            import tempfile
+            import shutil
+
+            # Import safetensors exception to catch wrapped Windows errors
+            try:
+                from safetensors.torch import SafetensorError
+            except ImportError:
+                SafetensorError = Exception  # Fallback if not available
+
+            max_retries = 10
+            base_delay = 0.2  # seconds
+            temp_dir = os.path.dirname(filename_original)
+
+            for attempt in range(max_retries):
+                try:
+                    # Force garbage collection and CUDA cache cleanup
+                    gc.collect()
+                    if torch.cuda.is_available():
+                        torch.cuda.empty_cache()
+
+                    # Create temp file in same directory for atomic replace
+                    with tempfile.NamedTemporaryFile(
+                        delete=False,
+                        dir=temp_dir,
+                        suffix=".safetensors.tmp"
+                    ) as tmp_file:
+                        tmp_path = tmp_file.name
+
+                    try:
+                        # Write to temp file (safe - original untouched)
+                        save_file(tensors, tmp_path)
+
+                        # Only delete original after successful write
+                        if os.path.exists(filename_original):
+                            os.remove(filename_original)
+
+                        # Move temp to original location (atomic)
+                        shutil.move(tmp_path, filename_original)
+                        break  # Success
+
+                    except Exception as write_error:
+                        # Clean up temp file on write failure
+                        try:
+                            if os.path.exists(tmp_path):
+                                os.remove(tmp_path)
+                        except:
+                            pass
+                        raise write_error
+
+                except (OSError, IOError, SafetensorError) as e:
+                    # Catch both OS errors and safetensors-wrapped Windows errors
+                    error_msg = str(e).lower()
+                    is_lock_error = "1224" in error_msg or "user-mapped" in error_msg or "cannot be performed" in error_msg
+
+                    if is_lock_error and attempt < max_retries - 1:
+                        # Exponential backoff for lock errors
+                        delay = base_delay * (2 ** (attempt // 2))
+                        if UNSLOTH_ENABLE_LOGGING:
+                            logger.warning(
+                                f"[Retry {attempt + 1}/{max_retries}] Windows file lock detected: {e}. "
+                                f"Waiting {delay:.1f}s before retry..."
+                            )
+                        time.sleep(delay)
+                    elif is_lock_error and attempt == max_retries - 1:
+                        raise RuntimeError(
+                            f"Failed to save file after {max_retries} attempts due to Windows file lock. "
+                            "Original shard preserved - no data loss. "
+                            "Solutions: 1) Restart Unsloth Studio 2) Disable antivirus 3) Close File Explorer windows"
+                        )
+                    else:
+                        # Non-lock errors - fail immediately
+                        raise RuntimeError(f"Model merge failed with error: {e}")
+
             del tensors
 
         if torch.cuda.is_available():