This mega patch primarily introduces a new function engine. The main
reasons for this new engine are:
1) Massively improved performance with lock-contended graphs.
Certain large function graphs could have very high lock-contention which
turned out to be much slower than I would have liked. This new algorithm
happens to be basically lock-free, so that's another helpful
improvement.
2) Glitch-free function graphs.
The function graphs could "glitch" (an FRP term) which could be
undesirable in theory. In practice this was never really an issue, and
I've not explicitly guaranteed that the new graphs are provably
glitch-free, but in practice things are a lot more consistent.
3) Simpler graph shape.
The new graphs don't require the private channels. This makes
understanding the graphs a lot easier.
4) Branched graphs only run half.
Previously we would run two pure side of an if statement, and while this
was mostly meant as an early experiment, it stayed in for far too long
and now was the right time to remove this. This also means our graphs
are much smaller and more efficient too.
Note that this changed the function API slightly. Everything has been
ported. It's possible that we introduce a new API in the future, but it
is unexpected to cause removal of the two current APIs.
In addition, we finally split out the "schedule" aspect from
world.schedule(). The "pick me" aspects now happen in a separate
resource, rather than as a yucky side-effect in the function. This also
lets us more precisely choose when we're scheduled, and we can observe
without being chosen too.
As usual many thanks to Sam for helping through some of the algorithmic
graph shape issues!
It's a normally named function for now, until we think of a common
package to move it into.
Hopefully this makes improving the lexer and parser easier for now. We
can consider bringing it back if needed.
Since we focus on safety, it would be nice to reduce the chance of any
runtime errors if we made a typo for a resource parameter. With this
patch, each resource can export constants into the global namespace so
that typos would cause a compile error.
Of course in the future if we had a more advanced type system, then we
could support precise types for each individual resource param, but in
an attempt to keep things simple, we'll leave that for another day. It
would add complexity too if we ever wanted to store a parameter
externally.
Lastly, we might consider adding "special case" parsing so that directly
specified fields would parse intelligently. For example, we could allow:
file "/tmp/hello" {
state => exists, # magic sugar!
}
This isn't supported for now, but if it works after all the other parser
changes have been made, it might be something to consider.
This might be slightly controversial, in that you must specify the state
if a file would need to be created to perform the action. We no longer
implicitly assume that just specifying content is enough. As it turns
out, I believe this is safer and more correct. The code to implement
this turns out to be much more logical and simplified, and does this
removes an ambiguous corner case from the reversed resource code.
Some discussion in: https://github.com/purpleidea/mgmt/issues/540
This patch also does a bit of related cleanup.
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.
