OSError: [Errno 22] Invalid argument on Windows when flushing stderr

[Jorisslagter]

Description

ComfyUI crashes on Windows (Desktop app) with OSError: [Errno 22] Invalid argument when the tqdm progress bar tries to flush stderr during sampling.

Environment

• OS: Windows 11
• ComfyUI Version: 0.6.0
• ComfyUI-Manager: 4.0.4
• Python: 3.12.11
• PyTorch: 2.8.0+cu129
• GPU: NVIDIA GeForce RTX 5080
• Using ComfyUI Desktop app

Error Stack Trace

File "comfyui_manager/prestartup_script.py", line 346, in flush
    original_stderr.flush()
File "C:\Users\...\ComfyUI\app\logger.py", line 35, in flush
    super().flush()
OSError: [Errno 22] Invalid argument

Full traceback

The error occurs in the sampling loop when tqdm tries to display progress:

File "comfy/k_diffusion/sampling.py", line 188, in sample_euler
    for i in trange(len(sigmas) - 1, disable=disable):
File "tqdm/std.py", line 448, in status_printer
    getattr(sys.stderr, 'flush', lambda: None)()
File "comfyui_manager/prestartup_script.py", line 346, in flush
    original_stderr.flush()
OSError: [Errno 22] Invalid argument

Cause

The flush() method in prestartup_script.py line 342-346 doesn't handle the case where original_stderr is a special Windows handle (from ComfyUI Desktop app) that doesn't support the flush operation.

Suggested Fix

Add try-except around the flush call in prestartup_script.py:

with std_log_lock:
    try:
        if self.is_stdout:
            original_stdout.flush()
        else:
            original_stderr.flush()
    except OSError:
        pass  # Ignore flush errors on Windows

Workaround

Users can manually apply this fix to prestartup_script.py to prevent the crash.