alts? throws alts! used not in (go ...) block

[laurentsenta]

Hi,
First, thanks for sharing this lib and the rest of you work (konserve, etc) with the community.

I get an unexpected exception with alts?:

;; http://stackoverflow.com/questions/30766215/how-do-i-unit-test-clojure-core-async-go-macros/30781278#30781278
(defn test-within
  "Asserts that ch does not close or produce a value within ms. Returns a
  channel from which the value can be taken."
  [ms ch]
  (go-try S
    (let [t (timeout ms)
          [v ch] (alts? S [ch t])]
      (is (not= ch t)
          (str "Test should have finished within " ms "ms."))
      v)))

(test-within 100 
  (go-try S 1))

(S is the default supervisor).

Throws:

=> #object[cljs.core.async.impl.channels.ManyToManyChannel]
Supervisor: #object[Error Error: alts! used not in (go ...) block] Error: alts! used not in (go ...) block
    at Function.cljs.core.async.alts_BANG_.cljs$core$IFn$_invoke$arity$variadic (http://localhost:3002/js/testbook.out/cljs/core/async.js:767:8)
    at cljs$core$async$alts_BANG_ (http://localhost:3002/js/testbook.out/cljs/core/async.js:760:35)
    at Function.superv.async.alts_QMARK_.cljs$core$IFn$_invoke$arity$variadic (http://localhost:3002/js/testbook.out/superv/async.js:673:45)
    at superv$async$alts_QMARK_ (http://localhost:3002/js/testbook.out/superv/async.js:667:33)
    at http://localhost:3002/js/testbook.out/budb/test/helpers.js?zx=rxrmkpegur10:623:43
    at http://localhost:3002/js/testbook.out/budb/test/helpers.js?zx=rxrmkpegur10:674:51
    at budb$test$helpers$test_within_$_state_machine__27340__auto____1 (http://localhost:3002/js/testbook.out/budb/test/helpers.js?zx=rxrmkpegur10:695:4)
    at budb$test$helpers$test_within_$_state_machine__27340__auto__ (http://localhost:3002/js/testbook.out/budb/test/helpers.js?zx=rxrmkpegur10:711:72)
    at cljs$core$async$impl$ioc_helpers$run_state_machine (http://localhost:3002/js/testbook.out/cljs/core/async/impl/ioc_helpers.js:93:110)
    at cljs$core$async$impl$ioc_helpers$run_state_machine_wrapped (http://localhost:3002/js/testbook.out/cljs/core/async/impl/ioc_helpers.js:96:63)
    at http://localhost:3002/js/testbook.out/budb/test/helpers.js?zx=rxrmkpegur10:726:67
    at cljs$core$async$impl$dispatch$process_messages (http://localhost:3002/js/testbook.out/cljs/core/async/impl/dispatch.js:20:9)

Using alts! instead behave as expected.

[raycheung]

Looks like the wrap-abort! inside alts? violates the restriction mentioned here.

[whilo]

@raycheung Correct. I thought Rich Hickey once said that alts! is a real function, not just syntax (macros), but it is not wrappable and I think one has to treat it as syntax and wrap it in a macro unfortunately.

@lsenta I think this has fixed it d291239. Thanks for reporting! Somehow it slipped through the tests, I have added one for it.

[whilo]

I will release a new version soon, unless you find other issues. 😃

[whilo]

@raycheung The function boundary wrapping is a bit cumbersome, but understandable. All JVM libraries supporting fibers (they mention Erjang, I also know it from pulsar) do bytecode transformations. I just wish they had covered error handling in core.async, so wrapping all of it wasn't necessary.

[laurentsenta]

Thanks for sharing the limitations post and providing a fix for this issue. No other issues on my side, I'll wait for the next release, try alts? again and let you know!

[whilo]

Fixed with 0.2.6 release :)