Default to the number of CPU cores, which seems about optimal
on my laptop. Using one more saves me 2 seconds actually.
Better packing of workers improves speed significantly.
In 2 tests runs, I saw segfaulting workers despite my attempt
to work around that issue. So detect when a worker does, and re-run it.
Removed installSignalHandlers again, because I was seeing an
error "lost signal due to full pipe", which I guess was somehow caused
by using it.
Sponsored-by: Dartmouth College's Datalad project
Note the very weird workaround for what appears to be some kind of tasty
bug, which causes a segfault. This is not new to this modification,
I was seeing a segfault before at least intermittently when limiting
git-annex test -p to only run a single test group.
Also, the path from one test repo to a remote test repo used to be
"../../foo", which somehow broke when moving the test repos from .t to
.t/N. I don't actually quite understand how it used to work, but
"../foo" seems correct and works in the new situation.
Test output from the concurrent processes is not yet serialized.
Should be easy to do using concurrent-output.
More test groups will probably make the speedup larger. It would
probably be best to have a larger number of test groups and divvy them
amoung subprocesses numbered based on the number of CPU cores, perhaps
times 2 or 3.
Sponsored-by: Dartmouth College's Datalad project
