Re: [PATCH] index-pack: protect deepest_delta in multithread code
- From
Thomas Rast <trast@student.ethz.ch>
- Date
- Mar 19, 2013, 13:50 UTC
- Message-ID
- <87d2uv7b31.fsf@pctrast.inf.ethz.ch>
- In-Reply-To
- <1363698075-12452-1-git-send-email-pclouds@gmail.com>
Nguyễn Thái Ngọc Duy <pclouds@gmail.com> writes:
Show 11 quoted lines
> deepest_delta is a global variable but is updated without protection > in resolve_delta(), a multithreaded function. Add a new mutex for it, > but only protect and update when it's actually used (i.e. show_stat is > non-zero). > > Another variable that will not be updated is delta_depth in "struct > object_entry" as it's only useful when show_stat is 1. Putting it in > "if (show_stat)" makes it clearer. > > The local variable "stat" is renamed to "show_stat" after moving to > global scope because the name "stat" conflicts with stat(2) syscall.
Looks good to me, too. However, I think it would still be less magical if we had the below too. It also silences helgrind.
-- >8 -- Subject: [PATCH] index-pack: guard nr_resolved_deltas reads by lock
The threaded parts of index-pack increment the number of resolved deltas in nr_resolved_deltas guarded by counter_mutex. However, the per-thread outer loop accessed nr_resolved_deltas without any locks.
This is not wrong as such, since it doesn't matter all that much whether we get an outdated value. However, unless someone proves that this one lock makes all the performance difference, it would be much cleaner to guard _all_ accesses to the variable with the lock.
Signed-off-by: Thomas Rast <trast@student.ethz.ch> --- builtin/index-pack.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/builtin/index-pack.c b/builtin/index-pack.c index b3fee45..6be99e2 100644 --- a/builtin/index-pack.c +++ b/builtin/index-pack.c @@ -968,7 +968,9 @@ static void *threaded_second_pass(void *data) for (;;) { int i; work_lock(); + counter_lock(); display_progress(progress, nr_resolved_deltas); + counter_unlock(); while (nr_dispatched < nr_objects && is_delta_type(objects[nr_dispatched].type)) nr_dispatched++;
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1.8.2.487.g725f6bb
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Thomas Rast
trast@{inf,student}.ethz.ch