`ev/select` still revives fibers....

[amano-kenji]

In production code, when ev/select is called again, It even runs defer forms after they are run once...... They shouldn't be run again.... Because of this issue, I eliminated channel/from-each and ev/select in my production code.

This is my minimal example.

(import spork/stream)
(import spork/sh)
(import spork/channel)

(def chan (ev/chan))

(defn revive-fibers
  []
  (def /dev/null (sh/devnull))
  (defer (do
           (:close /dev/null)
           (eprint "/dev/null closed"))
    (def proc (os/spawn ["sleep" "10000000000"]
                        :p {:out :pipe :err /dev/null}))
    (defer (do
             (:close proc)
             (eprint "proc closed"))
      (def lines (channel/from-each (stream/lines (proc :out))))
      (ev/spawn
        (ev/sleep 2)
        (:kill proc false :term))
      (match (ev/select chan lines)
        [:close c]
        (eprint "lines closed naturally")))))

(def supervisor (ev/chan))
(ev/spawn
  (forever
    (let [[status fiber] (ev/take supervisor)]
      (eprintf "status: %n, fiber: %n, fiber/last-value: %n" status fiber
               (fiber/last-value fiber)))))
(ev/go revive-fibers nil supervisor)

Output is

status: :ok, fiber: <fiber 0x55CFED05D6C0>, fiber/last-value: <core/process 0x55CFED0595F0>
status: :ok, fiber: <fiber 0x55CFED05D010>, fiber/last-value: nil
lines closed naturally
status: :ok, fiber: <fiber 0x55CFED05D340>, fiber/last-value: nil
status: :error, fiber: <fiber 0x55CFED05D340>, fiber/last-value: nil
proc closed
/dev/null closed
status: :ok, fiber: <fiber 0x55CFED05CB10>, fiber/last-value: nil

I noticed that the iterable task of channel/from-each was not really cancelled because ev/select didn't return a value in channel/from-each.

[bakpakin]

Hard to say for certain yet (I'm looking into this) but I think the issue is with channel/from-each looking for specific errors and then calling propagate.

[amano-kenji]

I'm thinking that I'm using ev/select wrong. In the above example, ev/select is called twice on the same channel.

[bakpakin]

So on latest master, this seems to work as expected (as I expected). I wrapped every call to ev/go and ev/spawn with tracev so we can see which fibers are created, and then added this bit of code to monitor which fibers are active:

(forever
  (ev/sleep 1)
  (def all-tasks (ev/all-tasks))
  (def me (fiber/root))
  (def sans-self (seq [t :in all-tasks :when (not= me t)] t))
  (printf "%n" sans-self))

At the end, a single fiber is left running that corresponds to the loop that is reading from the supervisor channel via (ev/spawn (forever ...))

Closing as cannot reproduce, please reopen if still an issue.