Am 15.08.2017 um 14:53 schrieb Martin Ågren:
When checking the conditional of "while (me->remaining)", we did not hold the lock. Calling find_deltas would still be safe, since it checks "remaining" (after taking the lock) and is able to handle all values. In fact, this could (currently) not trigger any bug: a bug could happen if `remaining` transitioning from zero to non-zero races with the evaluation of the while-condition, but these are always separated by the data_ready-mechanism.Make sure we have the lock when we read `remaining`. This does mean we release it just so that find_deltas can take it immediately again. We could tweak the contract so that the lock should be taken before calling find_deltas, but let's defer that until someone can actually show that "unlock+lock" has a measurable negative impact. Signed-off-by: Martin Ågren <martin.ag...@gmail.com> --- I don't think this corrects any real error. The benefits of this patch would be "future-proofs things slightly" and "silences tsan, so that other errors don't drown in noise". Feel free to tell me those benefits are negligible and that this change actually hurts. builtin/pack-objects.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c index c753e9237..bd391e97a 100644 --- a/builtin/pack-objects.c +++ b/builtin/pack-objects.c @@ -2170,7 +2170,10 @@ static void *threaded_find_deltas(void *arg) { struct thread_params *me = arg;+ progress_lock();while (me->remaining) { + progress_unlock(); + find_deltas(me->list, &me->remaining, me->window, me->depth, me->processed);@@ -2192,7 +2195,10 @@ static void *threaded_find_deltas(void *arg)pthread_cond_wait(&me->cond, &me->mutex); me->data_ready = 0; pthread_mutex_unlock(&me->mutex); + + progress_lock(); } + progress_unlock(); /* leave ->working 1 so that this doesn't get more work assigned */ return NULL; }
It is correct that this access of me->remaining requires a lock. It could be solved in the way you did. I tried to do it differently, but all cleaner solutions that I can think of are overkill...
-- Hannes
