util: improve iterfile so it chooses code path wisely
We have performance concerns on "iterfile" as it is 4X slower on normal
files. While modern systems have the nice property that reading a "fast"
(on-disk) file cannot be interrupted and should be made use of.
This patch dumps the related knowledge in comments. And "iterfile" chooses
code paths wisely:
1. If it's CPython 3, or PyPY, use the fast path.
2. If fp is a normal file, use the fast path.
3. If fp is not a normal file and CPython version >= 2.7.4, use the same
workaround (4x slower) as before.
4. If fp is not a normal file and CPython version < 2.7.4, use another
workaround (2x slower but may block longer then necessary) which
basically re-invents the buffer + readline logic in Python.
This will give us good confidence on both correctness and performance
dealing with EINTR in iterfile(fp) for all known supported Python versions.
#require execbit
Create extension that can disable exec checks:
$ cat > noexec.py <<EOF
> from mercurial import extensions, util
> def setflags(orig, f, l, x):
> pass
> def checkexec(orig, path):
> return False
> def extsetup(ui):
> extensions.wrapfunction(util, 'setflags', setflags)
> extensions.wrapfunction(util, 'checkexec', checkexec)
> EOF
$ hg init unix-repo
$ cd unix-repo
$ touch a
$ hg add a
$ hg commit -m 'unix: add a'
$ hg clone . ../win-repo
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ chmod +x a
$ hg commit -m 'unix: chmod a'
$ hg manifest -v
755 * a
$ cd ../win-repo
$ touch b
$ hg add b
$ hg commit -m 'win: add b'
$ hg manifest -v
644 a
644 b
$ hg pull
pulling from $TESTTMP/unix-repo
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg manifest -v -r tip
755 * a
Simulate a Windows merge:
$ hg --config extensions.n=$TESTTMP/noexec.py merge --debug
searching for copies back to rev 1
unmatched files in local:
b
resolving manifests
branchmerge: True, force: False, partial: False
ancestor: a03b0deabf2b, local: d6fa54f68ae1+, remote: 2d8bcf2dda39
a: update permissions -> e
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
Simulate a Windows commit:
$ hg --config extensions.n=$TESTTMP/noexec.py commit -m 'win: merge'
$ hg manifest -v
755 * a
644 b
$ cd ..