bpo-33671 / shutil.copyfile: use memoryview() with dynamic size on Windows (#7681)

bpo-33671
* use memoryview() with size == file size on Windows, see https://github.com/python/cpython/pull/7160#discussion_r195405230
* release intermediate (sliced) memoryview immediately
* replace "OSX" occurrences with "macOS"
* add some unittests for copyfileobj()

1 files changed, 7 insertions, 8 deletions

diff --git a/Misc/NEWS.d/next/Library/2018-05-28-23-25-17.bpo-33671.GIdKKi.rst b/Misc/NEWS.d/next/Library/2018-05-28-23-25-17.bpo-33671.GIdKKi.rst
index 5fd7e1f..b1523f2 100644
--- a/Misc/NEWS.d/next/Library/2018-05-28-23-25-17.bpo-33671.GIdKKi.rst
+++ b/Misc/NEWS.d/next/Library/2018-05-28-23-25-17.bpo-33671.GIdKKi.rst
@@ -1,11 +1,10 @@
 :func:`shutil.copyfile`, :func:`shutil.copy`, :func:`shutil.copy2`,
 :func:`shutil.copytree` and :func:`shutil.move` use platform-specific
-fast-copy syscalls on Linux, Solaris and OSX in order to copy the file
-more efficiently. All other platforms not using such technique will rely on a
-faster :func:`shutil.copyfile` implementation using :func:`memoryview`,
-:class:`bytearray` and
-:meth:`BufferedIOBase.readinto() <io.BufferedIOBase.readinto>`.
-Finally, :func:`shutil.copyfile` default buffer size on Windows was increased
-from 16KB to 1MB. The speedup for copying a 512MB file is about +26% on Linux,
-+50% on OSX and +38% on Windows. Also, much less CPU cycles are consumed
+fast-copy syscalls on Linux, Solaris and macOS in order to copy the file
+more efficiently.
+On Windows :func:`shutil.copyfile` uses a bigger default buffer size (1 MiB
+instead of 16 KiB) and a :func:`memoryview`-based variant of
+:func:`shutil.copyfileobj` is used.
+The speedup for copying a 512MiB file is about +26% on Linux, +50% on macOS and
++40% on Windows. Also, much less CPU cycles are consumed.
 (Contributed by Giampaolo Rodola' in :issue:`25427`.)