RR History/Checkpoints and can_add_checkpoint

Benoit Girard bgirard at mozilla.com
Sat Jan 23 04:41:48 UTC 2016

Jeff and Ehsan, today I said that I got into a state where RR checkpoints
where not working. Turns out that there's timeline.can_add_checkpoint()
which returns false in area where RR can't clone.

This is a problem for the history and checkpoint commands. For some reason
in 'mozilla::layers::ClientLayerManager::EndEmptyTransaction' I can't
create checkpoint so the limitation is a lot than just mostly in syscall as
the code is implying.

To create a lightweight GdbServer Checkpoint you only need a timeline
mark(), not an explicitly/heavyweight timeline checkpoint (clone). However
that function warns that it might need to seek and can be costly.

Roc, do you have any suggestions on how to precede with implementing the
History command and improving the reliability of gdb Checkpoint?
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