On 26/09/18 17:00, Alan Bateman wrote:
The reason that we've mentioned it a few times is because it's a significant issue. If you have a byte buffer then you can't have different threads accessing different parts of the buffer at the same time, at least not with any of the relative get/put methods as they depend on the buffer position. Sure you can globally synchronize all operations but you'll likely want much finer granularity. This bugbear comes up periodically, particularly when using buffers for cases that they weren't really designed for. Stuart pointed out the lack of absolute bulk get/put operations which is something that I think will help some of these cases.
Ok, I see that there is an issue here where only byte puts at absolute positions can be performed concurrently (assuming threads know how to avoid overlapping writes) while, by contrast, cursor-based byte[] stores require synchronization. Is that the problem in full? Or is there still more that I have missed? I certainly agree that a retro-fit to ByteBuffer which provided for byte[] puts at absolute positions would be of benefit for this proposal. However, such a retro-fix would be equally as useful for volatile memory buffers. I am not clear why this omission suggests to you that we should look at a new, alternative model for managing this particular type of mapped memory rather than just fixing the current one properly for all buffers.
Also, can you explain what you mean by confinement? (thread confinement?). Yes, thread vs. global. I haven't been following Panama close enough to say how this is exposed in the API.
Well, my vague stab was obviously in the right ballpark but I'm afraid I still don't know what baseball is. Could you explain what you mean by confinement?
Also, I don't think I would label this API an attempt to develop a file system. I think that's rather and overblown characterisation of what it does. I think you may have mis-read my mail as was just picking another example where MBB would be problematic.
Apologies for my very evident confusion here. I'd be very grateful if you could talk down a notch or two and/or amplify a bit more to help the hard of thinking.
I'm still not quite sure where this reply leaves the JEP though. Shall I update the Risks and Assumptions section to include mention of JDK-5029431 as suggested to Stuart? Is there anything else I can do to progress things?
It wouldn't do any harm to have this section mention that an alternative that exposes a more memory centric API may be possible in the future. Ok, I'll certainly add that.
regards, Andrew Dinn ----------- Senior Principal Software Engineer Red Hat UK Ltd Registered in England and Wales under Company Registration No. 03798903 Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander