On 5/16/2013 5:30 PM, Brett Cannon wrote:
On Thu, May 16, 2013 at 5:19 PM, Guido van Rossum <gu...@python.org> wrote:
This reminds me of the following bug, which can happen when two
processes are both writing the .pyc file and a third is reading it.
First some background.
When writing a .pyc file, we use the following strategy:
- open the file for writing
- write a dummy header (four null bytes)
- write the .py file's mtime
- write the marshalled code object
- replace the dummy heaer with the correct magic word
Just so people know, this is how we used to do it. In importlib we
write the entire file to a temp file and then to an atomic rename.
Even py_compile.py (used by compileall.py) uses this strategy.
py_compile as of Python 3.4 now just uses importlib directly, so it
matches its semantics.
But in 3.3, it still is as Guido describes, even though importlib is
improved.
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