The examples use the 2013-07-24 snapshot of core.async. At the time of writing, the API is still in flux and very experimental.
[org.clojure/core.async "0.1.0-SNAPSHOT"]
from:
["sonatype-oss-public" "https://oss.sonatype.org/content/repositories/snapshots/"]
Once upon a time, Alice wanted to invite Bob to an awesome party she had heard about, but she didn’t know where the party is going to be yet. So, she told Bob to wait by his phone, and she would send him the location, when she found out.
Unfortunately for them, the police were monitoring all the text messages. So, the police showed up, about an hour after the party had started, and arrested everyone for underage drinking.
Broadcasting
Alice, now feeling bad about the last party, decided to make it up to Bob and Carol by inviting them both to the next party she heard about. But, this time, she wanted to make sure no one else could see the message. So, she made a Facebook group, and only included Bob and Carol.
Unfortunately for them, the police were monitoring all the Facebook groups and messages. So, the police showed up, about an hour after the party had started, and arrested everyone for underage drinking.
Chaining Go Blocks
Alice decided to try one more time. This time also including Dave, to make up for the last failed party. But, Alice was getting slightly paranoid, so she decided to only tell Bob the location of the party, then have Bob tell Carol, and then have Carol pass it on to Dave.
Unfortunately for them, Dave got pulled over by the police, for a broken tail light, on his way to the party. Being within one hundred miles of the border, the police searched his car and found the handwritten note from Carol. So, the police showed up, about an hour after the party had started, and arrested everyone for underage drinking.
Timeouts
With this being the third time Alice, Bob, Carol, Dave, and Eve had appeared in his court, Judge Frank was ready to throw them in jail. In each case he decided to sentence them to several months in jail, based on their honesty (represented by a random number), with the option of letting them out early on good behavior (represented by an extra channel for each person).
Takeaways:
- Go blocks will block and execute in their own thread pool or, for the cljs version, their own state-machine-context-like-thing.
- The broadcast and multiplex (a.k.a. fan-out and fan-in) currently exist only as experiments. I hope they get rolled into the library, because I don’t want to have to write them myself.
- There is no “wait for all channels to have a value” function. Alts! and Multiplex return on the first channel to have a value.
- It looks like you could change the underlying channel implementation to something like a ZeroMQ (zmq-async) or RabbitMQ, but i’m not sure if it would actually be a useful abstraction.
