When debugging our project I find something interesting. In PyOS_Readline it releases the GIL and delegate its job to PyOS_ReadlineFunctionPointer, which could be call_readline or PyOS_StdioReadline(I don't find where vms__StdioReadline is defined). But in the two functions, they use some C APIs like PyMem_Malloc/MALLOC, PyErr_SetString which need guarded by GIL. I don't understand why not doing find-grained lock control in call_readline or PyOS_StdioReadline since the code is ancient. :-(

I find this because our project makes test_cmd_line fail with `echo "Timer\n" | python -i -m timeit -n 1`.