Eric Blake <ebl...@redhat.com> writes: > On 02/02/2018 07:03 AM, Markus Armbruster wrote: >> A massive number of objects depends on QAPI-generated headers. In my >> "build everything" tree, it's roughly 4500 out of 4800. This is >> particularly annoying when only some of the generated files change, >> say for a doc fix. >> >> Improve qapi-gen.py to touch its output files only if they actually >> change. Rebuild time for a QAPI doc fix drops from many minutes to a >> few seconds. Rebuilds get faster for certain code changes, too. For >> instance, adding a simple QMP event now recompiles less than 200 >> instead of 4500 objects. But adding a QAPI type is as bad as ever; we >> clearly got more work to do. > > The last phrase sounds quite colloquial. It may have been intentional; > but if not, s/we/we've/
I'll change it. >> Signed-off-by: Markus Armbruster <arm...@redhat.com> >> --- >> scripts/qapi/common.py | 11 +++++++++-- >> 1 file changed, 9 insertions(+), 2 deletions(-) >> >> diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py >> index cfa2671ca3..be0fcc548a 100644 >> --- a/scripts/qapi/common.py >> +++ b/scripts/qapi/common.py >> @@ -1944,9 +1944,16 @@ class QAPIGen(object): >> except os.error as e: >> if e.errno != errno.EEXIST: >> raise >> - f = open(os.path.join(output_dir, fname), 'w') >> - f.write(self.top(fname) + self._preamble + self._body >> + fd = os.open(os.path.join(output_dir, fname), >> + os.O_RDWR | os.O_CREAT, 0666) >> + f = os.fdopen(fd, 'r+') >> + text = (self.top(fname) + self._preamble + self._body >> + self.bottom(fname)) >> + oldtext = f.read(len(text) + 1) >> + if text != oldtext: >> + f.seek(0) >> + f.truncate(0) >> + f.write(text) > > In-memory rewrite rather than playing games with a secondary file > combined with the rename(2) syscall. It means you're not atomic (an > external reader has a window of time where they can see an incomplete > version of the file). Same as before. > But I think make dependency rules mean we don't > care - even in a parallel rule, as long as all clients depend on the > timestamp file, and the timestamp file isn't updated until all our > rewrites (if any) have settled, then we don't create any of those > external readers that can find the window of incomplete contents. > > Reviewed-by: Eric Blake <ebl...@redhat.com> Thanks!
