Sig inports for Const nodes

[emil14]

Can we avoid using lock by introducing sig inport to constant? What are upsides and downsides?

Related to #106

[emil14]

Problem №1 - We still need locks

TLDR: we can't use Const without locks no matter what triggers them (either we trigger them manually like this discussion suggests or they are triggered automatically like current implementation does). Const's receiver will receive too much messages.

This is how current approach works

There is const node that sends messages in infinite loop.

When we need to send message from const node to some other node, we use lock

We lock const's message at lock.v and use some kind of signal at lock.sig to unlock the message. This the mechanism that prevents receiving more messages that we need by receiver node.

This is how it will work without lockers (and with sig inport in Const)

Without locks const nodes will deliver multiple messages to their receiver nodes.

E.g. we want send helloWorld to print.v. We still need some kind of signal to trigger const right? Let that would be enter inport. We have our enter fired exactly once - this is how runtime works.

But after we trigger enter -> helloWorld we cannot know how many messages const actually will send. Actually it will send as many as buffer can fit and as fast as printer can read. It's possible in theory that print will print several messages before we exit the program.

I.e. without lock we can't control how many messages print will receive even though we want it to receive exactly once (current solution with locks gives us such control)

Possible solution - send one message per signal (no infinite sending)

Send only one message per each const trigger

The problem with possible solution

Initial inports use-case. E.g. we have some requestSender node with 2 inports url and data. Data is dynamic but URL is always the same (static).

With this approach we will block after first firing. requestSender will probably block forever while waiting the second "pair" of messages. It will receive second value for data but second URL will never arrive.

But we of-course can use data as a trigger signal for url const node (TODO think about this)

[emil14]

Problem №2 - $ sugar

How it works now

Let's take a look at infamous hello world example

in.enter -> lock.sig
$msg -> lock.v
lock.v -> print.v
print.v -> out.exit

We use $msg syntax sugar to create msg const node (instance of Const component)

How it will work

in.enter -> $msg.v
$msg.v -> print.v
print.v -> out.exit

What I don't like about this is

1. The need to specify v port - it's not obvious where this comes from (I have to know about stdlib which means I have to know about how this sugar is implemented)
2. Isn't it weird to have implicit $msg node? (Not sure about this one)

[emil14]

We're stick with current implementation

Explanation added in docs

76ace2b