This giant patch makes some much needed improvements to the code base.
* The engine has been rewritten and lives within engine/graph/
* All of the common interfaces and code now live in engine/
* All of the resources are in one package called engine/resources/
* The Res API can use different "traits" from engine/traits/
* The Res API has been simplified to hide many of the old internals
* The Watch & Process loops were previously inverted, but is now fixed
* The likelihood of package cycles has been reduced drastically
* And much, much more...
Unfortunately, some code had to be temporarily removed. The remote code
had to be taken out, as did the prometheus code. We hope to have these
back in new forms as soon as possible.
The golang race detector complains about some unimportant races, and as
a result, this patch adds some mutexes to prevent these test failures.
We actually lock more than necessary, because a more accurate version
would be more time consuming to implement. Secondarily, it's likely that
in the future we replace this function graph algorithm with something
that is guaranteed to be glitch-free and supports back pressure.
I noticed a very intermittent test failure where interpret would end up
running, but *fail* because a value wasn't present. This should never
happen, because the function engine is designed to only call interpret
when there has been at least one value produced for every node in the
AST. So what is the bug that would produce:
interpret error: could not interpret: func value does not yet exist
About 20 minutes ago while I was getting to bed, it occurred to me where
to look! Out of bed and to the laptop, and after briefly reminding
myself of the code, I think I've found the issue.
What I think was happening, was that an AST node would produce a value,
and send a message on the aggregate channel. This channel is monitored,
and every time it receives a message, it checks to ensure that all the
values now exist before producing a message for interpret to run.
However, this AST node was not the final one to be produced, but before
the message was read by the aggregate channel, the last remaining AST
node ran and set it's "loaded" state to `true`, but *before* its value
was made available for the aggregate channel to read. That channel then
occasionally won the race and tried to access a value before it existed,
thus causing out intermittent bug.
At least I think that's what was going on. Hopefully this patch fixes
this, if not, then there's another bug hiding too! And of course, this
entire function engine could do with some proper analysis from someone
familiar with glitches, back pressure, and FRP parallelism.
One particular note was that I used my brain, not some fancy debugging
tool to find this. Maybe skilled debuggers can fork lift their tools
onto this type of problem, but I haven't those skills!
¯\_(ツ)_/¯
This is an initial implementation of the mgmt language. It is a
declarative (immutable) functional, reactive, domain specific
programming language. It is intended to be a language that is:
* safe
* powerful
* easy to reason about
With these properties, we hope this language, and the mgmt engine will
allow you to model the real-time systems that you'd like to automate.
This also includes a number of other associated changes. Sorry for the
large size of this patch.
