web 合成时候报错 MemoryError: Cannot allocate write+execute memory for ffi.callback().

**Summary[问题简述（一句话）]**
使用web版本合成的时候，提示这个：
MemoryError: Cannot allocate write+execute memory for ffi.callback(). You might be running on a system that prevents this. For more information, see https://cffi.readthedocs.io/en/latest/using.html#callbacks
127.0.0.1 - - [2022-03-23 16:52:59] "POST /api/synthesize HTTP/1.1" 500 426 14.242760

**Env & To Reproduce[复现与环境]**
mac m1
用的75k steps 用3个开源数据集混合训练

**Screenshots[截图（如有）]**

Reproduce the web synthesis failure on a Mac M1 and trace the POST /api/synthesize path to the cffi.callback() allocation described in the error. Read the linked cffi callback documentation and compare the failing environment with a working one; done means web synthesis completes without the MemoryError or HTTP 500 response.

Written by the indexing model from the issue text.