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bpo-33671 / shutil.copyfile: use memoryview() with dynamic size on Windows - #7681
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...as it's considerably slower for smaller files; e.g. with a 8MiB file:
--- original
~/svn/cpython {33671-release-memoryview}$ ./python -m timeit -s "import
shutil; f1 = open('f1', 'rb'); f2 = open('f2', 'wb')"
"shutil.copyfileobj(f1, f2)"
200000 loops, best of 5: 1.64 usec per loop
--- _copybinfileobj()
~/svn/cpython {33671-release-memoryview}$ ./python -m timeit -s "import
shutil; f1 = open('f1', 'rb'); f2 = open('f2', 'wb')"
"shutil.copyfileobj(f1, f2)"
100000 loops, best of 5: 3.3 usec per loop
...and use it from copyfile() only if WINDOWS and file size >= 128 MiB
giampaolo
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vstinner
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Jun 14, 2018
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Both options are always exclusive? macOS might have sendfile() in the future, no?
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This is now outdated: I updated code to always use fcopyfile on OSX and leave sendfile() alone. This way we avoid invoking sendfile() on OSX which would fail anyway.
vstinner
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Jun 14, 2018
| # considerable speedup by using a readinto()/memoryview() | ||
| # variant of copyfileobj(), see: | ||
| # https://github.com/python/cpython/pull/7160#discussion_r195162475 | ||
| elif _WINDOWS and file_size >= 128 * 1024 * 1024: |
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Would you mind to add a top-level private constant rather than an hardcoded value? (Would it make sense to make it somehow public? Or add an optional parameter...?)
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This is outdated, I modified code to always use the readinto() variant regardless of file size, see: #7160 (comment)
As per #7160 (comment) it appears using memoryview() on Windows is faster also for small files if memoryview() length is equal to file size.
giampaolo
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This is a follow up of #7160.
Changes:
memoryview()with size == file size, see bpo-33671: efficient zero-copy for shutil.copy* functions (Linux, OSX and Win) #7160 (comment)memoryviewimmediatelyhttps://bugs.python.org/issue33671