As far as I can tell, this structure doesn't compose with well-defined semantics. Consider, e.g. x ++ y — what is the executor for such a composite?

It seems like we need to say three things:

• Invocation of "open" occurs on the blocking thread pool, which we can do in the reserve of the managed
• Invocation of "close" occurs on the blocking thread pool, which we can do in the reserve of managed (on finalization)
• Invocation of the "pull" occurs on the blocking thread pool, which we can also do (below, using effectBlocking instead of effectTotal, etc.).

So unless I'm missing something, we can do this w/o new machinery. Right? Or wrong? 😄

Say x: StreamEffect uses a Blocking executor, y: StreamEffect uses a regular executor, and z: Stream that is asynchronous.

(x ++ y ++ z).process does the following:

• opens x and starts pulling it. The Pull on x evaluates the () => A thunk while locked to the Blocking executor (StreamEffect.scala:34), so that pull runs on the blocking executor;
• opens y and starts pulling it. Similarly, it evaluates the thunk while locked to the default executor, so that pull runs there.
• opens z and starts pulling it. That Pull does whatever it wants because it's effectful.

From how I'm reading things, the semantics here are identical to the semantics of lock, as long as we always propagate the executor when composing StreamEffect values. Wdyt?

@jdegoes

Sorry, I realized I didn't respond to your questions about whether it's possible to do this without new machinery.

The problem is as follows: how does a constructor (like fromInputStream), which only produces a thunk Managed[E, () => A], indicate that when a stream which is based on it is run, it should be run on the Blocking threadpool? We can't use effectBlocking because we want to produce synchronous code that runs in the thunk.

@jdegoes Any thoughts on the above? :-)

I was busy with the huge ZSink rewrite PR, where are we with this?

@iravid @jdegoes

We hashed it over deadlift sets. I believe @jdegoes is onboard. I'll pick this back up next week :-)

Awesome. Please keep me in the review loop.