转换器如何在 core.async 通道中执行？答案

【问题标题】：How are transducers executed in core.async channels?转换器如何在 core.async 通道中执行？
【发布时间】：2016-01-18 05:32:46
【问题描述】：

当把频道变成这样的频道时：

(chan 10 tx)

如果我创建了 10 个这样的通道，然后同时向所有通道发送消息，传感器将如何执行。它们是并发运行还是在一个线程上运行？

【问题讨论】：

标签： clojure clojurescript core.async

【解决方案1】：

我认为现在转换器运行时的行为尚未定义，但查看ManyToManyChannel 的实现，转换器（即add! 字段）可以在写入和读取时调用频道。

运行一个简单的测试似乎是如果通道未满，写入线程会执行转换器，但如果通道已满，有时读取线程会运行它。

一个带有小缓冲区的样本：

(defn thread-name []
  (.getName (Thread/currentThread)))

(require '[clojure.core.async :as async :refer [chan <! >! >!! go]])

(defn p [& args]
  (locking *out*
          (apply println (thread-name) ":" args)))

(defn log [v]
  (p "Transforming" v)
  v)

(def tx (map log))

(def c (chan 1 tx))
(def c2 (chan 1 tx))

(go
  (loop []
    (when-let [v (<! c)]
      (p "Getting from c1" v)
      (<! (async/timeout 100))
      (recur))))

(go
  (loop []
    (when-let [v (<! c2)]
      (p "Getting from c2" v)
      (<! (async/timeout 100))
      (recur))))

(dotimes [_ 5]
  (p "Putting in c1" 1)
  (>!! c 1)
  (p "Putting in c2" 100)
  (>!! c2 100))

产生输出：

nREPL-worker-20 : Transforming 1
nREPL-worker-20 : Putting in c2 100
async-dispatch-33 : Getting from c1 1
nREPL-worker-20 : Transforming 100
nREPL-worker-20 : Putting in c1 1
async-dispatch-31 : Getting from c2 100
nREPL-worker-20 : Transforming 1
nREPL-worker-20 : Putting in c2 100
nREPL-worker-20 : Transforming 100
nREPL-worker-20 : Putting in c1 1
async-dispatch-35 : Getting from c2 100
async-dispatch-34 : Transforming 1 <---- In this case is run in the reading side
async-dispatch-34 : Getting from c1 1
nREPL-worker-20 : Putting in c2 100
nREPL-worker-20 : Transforming 100
async-dispatch-37 : Getting from c2 100
async-dispatch-36 : Getting from c1 1
nREPL-worker-20 : Putting in c1 1

【讨论】：