Write lock is an exclusive lock and no other threads can obtain read or
write lock while current thread holding write lock.
Why you think checking for current thread is lock-owner is not atomic?
A thread that already holds a write lock has no needs to obtain read locks
unless it releases the write-lock.
Your change can have serious impact.
Can you share a reproducer?
вт, 25 февр. 2020 г., 20:42 Дмитрий Горчаков <
dmitry.gorchakov.mu...@gmail.com>:
> > Could you please describe in detail the issue you are trying to fix?
>
> I once got same deadlock on a productive in v2.7.5. New iteration of
> checkpoint could not start. Dump attached.
>
> > By the way, please take a look at
> GridCacheDatabaseSharedManager.checkpointReadLock:
>
> Thanks, I will look more closely at this check.
>
> > So, do we really need to unconditionally unlock the read lock at
> checkpointReadUnlock as you propose?
>
> Checking for a writе lock holding through method isHeldByCurrentThread is
> not atomic, so there is no certainty that this thread still owns a write
> lock.
> I assume that a read lock was obtained and in this code we did not release
> it.
>
> Thanks!
>
> вт, 25 февр. 2020 г. в 14:35, Вячеслав Коптилин <slava.kopti...@gmail.com
> >:
>
>> Hello Dmitry,
>>
>> To be honest, I don't quite understand the proposed fix. Could you please
>> describe in detail the issue you are trying to fix?
>> By the way, please take a look at
>> GridCacheDatabaseSharedManager.checkpointReadLock:
>>
>> @Override public void checkpointReadLock() {
>> if (checkpointLock.writeLock().isHeldByCurrentThread())
>> return;
>> ...
>> }
>>
>> In other words, the read lock is not acquired in case the write lock is
>> already held.
>> So, do we really need to unconditionally unlock the read lock at
>> checkpointReadUnlock as you propose?
>>
>> Thanks,
>> S.
>>
>> вт, 25 февр. 2020 г. в 13:32, Dmitry Gorchakov <
>> dmitry.gorchakov.mu...@gmail.com>:
>>
>> > This issue once reproduced in my productive with similar stack trace.
>> > During
>> > sources analysis I saw the use unsafe of method
>> > writeLock().isHeldByCurrentThread() for unlocking checkpoint. This may
>> > cause
>> > thread to starvation. Problem no longer appeared after local fix.
>> > I prepared pull request https://github.com/apache/ignite/pull/7445.
>> > Accept please jira issue to me and review my PR.
>> >
>> >
>> >
>> >
>> > --
>> > Sent from: http://apache-ignite-developers.2346864.n4.nabble.com/
>> >
>>
>
