为什么我只拍一张！从这个频道？

Question

试图了解渠道的运作方式；我不明白为什么我的take! 在这个 REPL 序列中只工作一次，即使我在此过程中尝试了多次放置：

cplay.core> (def h (chan))
#'cplay.core/h
cplay.core> (go (put! h "hello"))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@4afdd6ba>
cplay.core> (go (take! h (fn [x] (println x))))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@9fe39a1>
cplay.core> hello

cplay.core> (go (take! h (fn [x] (println x))))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@206564e9>
cplay.core> (go (put! h "hello"))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@6c0ec468>
cplay.core> (go (take! h (fn [x] (println x))))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@60c85184>
cplay.core> (go (take! h (fn [x] (println x))))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@3edc08c3>
cplay.core> (go (take! h (fn [x] (println x))))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@6a7b295f>
cplay.core> (go (put! h "hello"))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@60331d8b>
cplay.core> (go (take! h (fn [x] (println x))))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@557c3bce>
cplay.core> (go (put! h "hello"))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@203fdcfb>
cplay.core> (go (put! h "hello"))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@ed11c1>
cplay.core> (go (take! h (fn [x] (println x))))
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@6c7ea146>
cplay.core> 

是不是因为当通道上没有任何东西时我连续几次从通道中取出，从而留下由后续 put 填充的“空白”，直到通道以某种方式恢复到偶数的 put 和 take？

Answer 1

在这种异步场景中，println 的行为非常奇怪。 如果您的最后一次调用是“take！” fn 那么你最终会在你的 repl 中得到打印结果，但是最后一次调用是“put！”。 fn 那么你必须在 nrepl-server 终端上找到打印结果。

在 core.async 的Timothy Baldridge video 开头引入了这种行为和必要的工作空间

这里是 one screenshot 我在 emacs 中的 2 个帧，一个用于 nrepl，另一个用于 nrepl-server 输出

Answer 2

不要用go 包裹put! 和take!。里面去你想要<!或!>：

user=> (require '[clojure.core.async :refer (chan put! take! <! >!)])
nil
user=> (def h (chan))
#'user/h
user=> (put! h "hello")
true
user=> (take! h println)
hello
nil
user=> (put! h "hello")
true
user=> (take! h println)
hello
nil
user=> (put! h "hello")
true
user=> (take! h println)
hello
nil
user=> (put! h "hello")
true
user=> (take! h println)
hello
nil
user=> (take! h println)
nil
user=> (put! h "hello")
hello
true