refactor(state): locks and concurrency

[mvayngrib]

for issue #17

let me know what you think

i factored out the locking/queueing logic into a separate module: multi-lock-queue, feel free to copy it over if you like. Actually, I coded it up a while back, when I first saw your issue and got curious about the problem. The code is short, should be pretty simple to follow, and there are tests. I took a look at async-lock, since you're already using it, but when I peeked inside the code, I got lost

the resulting changes of integrating the module are pretty straightforward. There's a queue that supports locks, and pausing it is the equivalent of waiting to acquire a global lock.

There were some unintended changes in the package-lock.json, no matter how many times I rimraf'd and re-installed, idk how you want to go about that. What version of npm are you using?

[smartcontracts]

So generally I'm a fan of the "standard" locking API of lock.acquire() and lock.release(). I know we started with the locking queue mechanism but may be easier to rewrite our existing stuff to do this by acquiring a lock once and doing everything synchronously or, if it's an operation that can happen async, have each "thread" acquire the lock for itself.

[smartcontracts]

As a general rule of thumb I like the idea of writing libraries for ourselves (for maintainability and security), so not relying on async-lock makes sense 👍

[mvayngrib]

@kfichter the problem with acquiring & releasing locks is you now have to do three jobs everywhere: lock, run something, and then release no matter what happens. Isn't it easier for the try/catch/finally to be abstracted away by enqueue()?

[smartcontracts]

Hmmm... that's true. It's part of why I like the syntax of async-lock - it's very similar to the with lock ... syntax in python that automatically releases the lock after execution.

[mvayngrib]

maybe we can just change the name/signature of enqueue. What would you prefer the invocation to look like? Something like await this._locks.withLocks(fn, locksArr) ? You tell me :)