FileIO, BufferedWriter left unflushed when ipy exits

[jameslan]

• Running the following code with ipy, will get an empty file test.txt, while with CPython, the file will have one byte 'a'

import io
out = io.FileIO('test.txt', 'w')
out.write(b'a')

• Similar case but using BufferedWriter:

import io
out = io.TextIOWrapper(io.BufferedWriter(io.FileIO('test.txt', 'w')))
out.write('a')

• Case involving stdio:

The following powershell command output nothing,

PS C:\Users\james\proj\ironpython3> .\bin\Debug\netcoreapp3.1\ipy.exe -c "import sys;sys.stdout.write('text')"
PS C:\Users\james\proj\ironpython3>

and the following powershell command could output the "text"

PS C:\Users\james\proj\ironpython3> .\bin\Debug\netcoreapp3.1\ipy.exe -c "import sys;sys.stdout.write('text\n')"
text
PS C:\Users\james\proj\ironpython3>

[slozier]

For the TextIOWrapper it seems like flush is called by __del__:

import io
class Test(io.TextIOWrapper):
    def __del__(self):
        pass
out = Test(io.BufferedWriter(io.FileIO('test.txt', 'w')))
out.write('a')

Probably similar for io.FileIO. For writing to standard streams it looks like CPython calls flush on sys.stdout and sys.stderr during Py_FinalizeEx. See https://github.com/python/cpython/blob/6c065594c720fdd4783a4284cb9f2eebcb2c10bd/Python/pylifecycle.c#L480-L502

[jameslan]

sys.stdout is TextIOWrapper(BufferedWriter(FileIO(Console.OpenStandardOutput()))) and sys.stderr is TextIOWrapper(BufferedWriter(FileIO(Console.OpenStandardError())))

So I think if TextIOWrapper or BufferedWriter could flush at exit, sys.stdout and sys.stderr should be good.

stdio are created here https://github.com/IronLanguages/ironpython3/blob/f32bf73f364c176db5cbbb6cefc6ec5f9fc92934/Src/IronPython/Runtime/PythonContext.cs#L1830-L1834

and https://github.com/IronLanguages/ironpython3/blob/f32bf73f364c176db5cbbb6cefc6ec5f9fc92934/Src/IronPython/Modules/_io.cs#L2847-L2859