Parallel cache push strawman

[acmorrow]

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated CHANGES.txt (and read the README.rst)
• I have updated the appropriate documentation

[acmorrow]

@bdbaddog - This seems to pass all tests, but please let me know if you would prefer to do this under a --experimental=??? flag and I can rework it like that.

[bdbaddog]

One concern/question.
Previously the node had .cached which you could use to see if the file was cached or not.
Now there's only a check to see if it shouldn't be cached, but no way to tell if the node has actually been cached?

Would restoring .cached break anything in this change?

[acmorrow]

One concern/question. Previously the node had .cached which you could use to see if the file was cached or not. Now there's only a check to see if it shouldn't be cached, but no way to tell if the node has actually been cached?

Would restoring .cached break anything in this change?

I don't think it would break anything to restore it. I took it out mostly because as far as I could see it was only being used to transfer info about caching from execute to executed, and we don't do that anymore. And I think the test that examined it will still need to go away. So it really will be more or less unused. Fine with me either way though.

[bdbaddog]

One concern/question. Previously the node had .cached which you could use to see if the file was cached or not. Now there's only a check to see if it shouldn't be cached, but no way to tell if the node has actually been cached?
Would restoring .cached break anything in this change?

I don't think it would break anything to restore it. I took it out mostly because as far as I could see it was only being used to transfer info about caching from execute to executed, and we don't do that anymore. And I think the test that examined it will still need to go away. So it really will be more or less unused. Fine with me either way though.

I think it's worth adding back in.
While not part of the published API, I can see someone useing it, and we may find it useful going forward with remote caching,etc..

[acmorrow]

One concern/question. Previously the node had .cached which you could use to see if the file was cached or not. Now there's only a check to see if it shouldn't be cached, but no way to tell if the node has actually been cached?
Would restoring .cached break anything in this change?

I don't think it would break anything to restore it. I took it out mostly because as far as I could see it was only being used to transfer info about caching from execute to executed, and we don't do that anymore. And I think the test that examined it will still need to go away. So it really will be more or less unused. Fine with me either way though.

I think it's worth adding back in. While not part of the published API, I can see someone useing it, and we may find it useful going forward with remote caching,etc..

@bdbaddog - done.