On Python 2, PyBytes_GET_SIZE is the same as PyString_GET_SIZE which
is the same as Py_SIZE which resolves to a struct member.
On Python 3, PyBytes_GET_SIZE is
"(assert(PyBytes_Check(op)),Py_SIZE(op))". The compiler barfs when
assigning to this version.
This patch simply changes PyBytes_GET_SIZE to Py_SIZE. On Python 2,
there is no effective change in behavior. On Python 3, we drop the
PyBytes_Check(). However, in all cases we have explicitly created
a PyBytesObject in the same function, so the PyBytes_Check() is
guaranteed to be true. Despite this, code changes over time, so
I've added added assert() in all callers so we can catch this in
debug builds.
With this patch, all mercurial.* C extensions now compile on Python 3
on my OS X machine. There are several compiler warnings and I'm sure
there are incompatibilities with Python 3, including possibly
segfaults. But it is a milestone.
Compiling mercurial with the Sun Studio compiler gives seven copies of the
following warning on pathencode.c:
line 533: warning: initializer will be sign-extended: -1
Using explicit unsigned literals silences it.
The Python version of this (see mercurial/store.py:_hashencode) copies path
components up to a limit of maxshortdirslen bytes. The Python version does not
consider the initial "dh/" to be part of the this, though, while the C version
currently does. Adding len("dh/") == 3 to the limit for the C version brings it
in line with the Python version.
This was not caught by the randomized testing scheme in test-pathencode.py
because of a couple of flaws with the test. Upcoming patches will fix those
problems.
This will be used by an upcoming patch.
This calls out to the Python hash implementation.
An earlier version of this function implemented SHA-1 directly, but
the amount of extra code didn't seem like a good tradeoff compared
to the small big-picture increase in performance (long paths are
uncommon).
(This is not yet enabled; it will be turned on in a followup patch.)
The path encoding performed by fncache is complex and (perhaps
surprisingly) slow enough to negatively affect the overall performance
of Mercurial.
For a short path (< 120 bytes), the Python code can be reduced to a fairly
tractable state machine that either determines that nothing needs to be
done in a single pass, or performs the encoding in a second pass.
For longer paths, we avoid the more complicated hashed encoding scheme
for now, and fall back to Python.
Raw performance: I measured in a repo containing 150,000 files in its tip
manifest, with a median path name length of 57 bytes, and 95th percentile
of 96 bytes.
In this repo, the Python code takes 3.1 seconds to encode all path
names, while the hybrid C-and-Python code (called from Python) takes
0.21 seconds, for a speedup of about 14.
Across several other large repositories, I've measured the speedup from
the C code at between 26x and 40x.
For path names above 120 bytes where we must fall back to Python for
hashed encoding, the speedup is about 1.7x. Thus absolute performance
will depend strongly on the characteristics of a particular repository.
Not yet used (will be enabled in a later patch).
This patch is a stripped down version of patches originally created by
Bryan O'Sullivan <bryano@fb.com>