Add channels example

[twetzel59]

Added an example that shows
how to use channels in a typical
multithreaded scenario.

[twetzel59]

This is just my second PR for Nim, so let me know if anything isn't quite right.

The example aims to be general but useful by explaining what I think most people might often do with channels.

[timotheecour]

could that code block be turned into a runnableExamples: ? that way it's guaranteed to always compile/run

[twetzel59]

@timotheecour, can runnableExamples work at module level? I wasn't quite sure how to use it l, so I searched the Nim repo and with a quick look I only saw it inside procs.

Many other modules have module level examples in a comment. Do they not use runnableExamples because they haven't been updates, or for a good reason?

[Araq]

This example mixes channels with threadpool and that's unwise. Also how the documentation of channels is generated is bad and needs to be changed.

[twetzel59]

Would it be better to use pure threads, or single threading instead?

[Araq]

Better show how to use plain threads with these channels.

[timotheecour]

@twetzel59

can runnableExamples work at module level?

just filed:

• runnableExamples doesn't work at module level runnableExamples doesn't work at module level #8641

IMO it'd be higher priority to fix this, so that you can add your example in top-level runnableExamples instead of adding more legacy code that'll later need to be changed to runnableExamples block.
But doesn't have to be you :-) If no-one volunteers I can look into it, but I have my hands full with a ton of other PR's at the moment.
I don't think it's a hard bug to fix

[timotheecour]

@timotheecour, can runnableExamples work at module level? I wasn't quite sure how to use it l, so I searched the Nim repo and with a quick look I only saw it inside procs.

it now works in devel

[twetzel59]

@timotheecour I have a question about the Git workflow here. My fork is quite old and doesn't have that fix yet. I assume I need to sync the fork.

Will doing so introduce an unwanted merge commit, or is that okay? Sorry, I'm a bit new to working on large projects :)

[timotheecour]

we really want to avoid merge commits, as discussed in another issue. Just do: git pull --rebase origin devel and then, if there are conflicts, resolve them. If you're having any issues in the process I'm happy to help

[Araq]

No progress, the example still uses the threadpool.