On 6/8/21 4:25 AM, Nicholas Piggin wrote:
Are shared pthread mutexes using existing pthread APIs that are today implemented okay with futex1 system call a good reason to constrain futex2 I wonder? Or do we have an opportunity to make a bigger change to the API so it suffers less from non deterministic latency (for example)?
If futex2 is not able to cover futex1 use cases then it cannot be viewed as a replacement. In the long term this means futex1 cannot be deprecated and has to be maintained. My impression was that futex1 was basically unmaintainable(*) and futex2 was an evolution of futex1 so that users of futex1 could migrate relatively easily and futex1 eventually removed. Maybe my impression was wrong, but I would like to see futex2 as a replacement and extension of futex1, so the latter can be deprecated at some point.
In any case, creating a new API should consider requirements of its potential users. If futex2 is intended to eventually replace futex1 then all current futex1 users are potential users of futex2. If not, then the futex2 submission should list its intended users, at least in general terms, and their requirements that led to the proposed API design.
(*) I use "unmaintainable" in a broad sense here. It exists and works in newer kernel versions and may receive code changes that are necessary to keep it working, but maintainers refuse any extensions or modifications of the code, mostly because of its complexity.
