bpo-17852: Maintain a list of BufferedWriter objects. Flush them on exit.#3372
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In Python 3, the buffer and the underlying file object are separate and so the order in which objects are finalized matters. This is unlike Python 2 where the file and buffer were a single object and finalization was done for both at the same time. In Python 3, if the file is finalized and closed before the buffer then the data in the buffer is lost. This change adds a doubly linked list of open file buffers. An atexit hook ensures they are flushed before proceeding with interpreter shutdown. This is addition does not remove the need to properly close files as there are other reasons why buffered data could get lost during finalization. Initial patch by Armin Rigo.
The previous implementation was not careful enough to avoid causing issues in multi-threaded cases. Check for buf->ok and buf->finalizing before actually doing the flush. Also, increase the refcnt to ensure the object does not disappear.
pitrou approved these changes Sep 6, 2017
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pitrou commented Dec 12, 2017
Sorry for not having caught this while reviewing, but the change here doesn't work. The problem is that |
nascheme added a commit to nascheme/cpython that referenced this pull request Dec 13, 2017
We can't use _Py_PyAtExit() as it only supports registering a single callback. It is used by the atexit module and so we can't use it. We can't use Py_AtExit() either because it calls functions too late in the interpreter shutdown process. Instead, create io._flush_all_buffers. In io.py, register it with the atexit module.
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This is a fixed (hopefully) version of my previous patch. Checking buf->ok and buf->finalizing is necessary, as suggested by Antoine Pitrou.
https://bugs.python.org/issue17852