clojure - core.async 与分区状态传感器不保持状态？

Question

(我之前有一个问题 here ，并假设我在访问 core.async 时不会遇到问题)。

给定如下输入数据:

(require '[clojure.core.async :as a])

(def input-data
  [{:itm_na 1 :seq_no 1  :doc_img "this is a very long "}
   {:itm_na 1 :seq_no 2  :doc_img "sentence from a mainframe "}
   {:itm_na 1 :seq_no 3  :doc_img "system that was built before i was "}
   {:itm_na 1 :seq_no 4  :doc_img "born."}
   {:itm_na 2 :seq_no 1  :doc_img "this is a another very long "}
   {:itm_na 2 :seq_no 2  :doc_img "sentence from the same mainframe "}
   {:itm_na 3 :seq_no 1  :doc_img "Ok here we are again. "}
   {:itm_na 3 :seq_no 2  :doc_img "The mainframe only had 40 char per field so"}
   {:itm_na 3 :seq_no 3  :doc_img "they broke it into multiple rows "}
   {:itm_na 3 :seq_no 4  :doc_img "which seems to be common"}
   {:itm_na 3 :seq_no 5  :doc_img " for the time. "}
   {:itm_na 3 :seq_no 6  :doc_img "thanks for your help."}])

partition-by (如预期)将我的数据聚集到 seq 中(以便稍后折叠):

(count (partition-by :itm_na input-data ))
;;=> 3

但是，当我出于某种原因尝试使用 core.async 管道执行此操作时，它 似乎没有做同样的事情...我如何获得有状态传感器部分 partition-by 在异步管道中实际上保留状态吗？

(let
    [source-chan (a/to-chan input-data)
     target-chan (a/chan 100)
     xf (comp (partition-by :itm_na))
     ]
  (a/pipeline 1
              target-chan
              xf
              source-chan)
  (count (<!! (a/into [] target-chan))))

;;=>12

这应该是3？

奇怪的是，当我将 xf 绑定(bind)到如下所示的 channel 时，我得到了预期的结果。我不确定为什么 a/pipeline 的行为不同。

(let [xf (comp (partition-by :itm_na))
      ch (a/chan 1 xf)]
  (a/onto-chan ch input-data)
  (count (<!! (a/into [] ch))))
=>3

从文档中...提到有状态位:

(clojure.repl/doc partition-by) 
-------------------------
clojure.core/partition-by
([f] [f coll])
  Applies f to each value in coll, splitting it each time f returns a
   new value.  Returns a lazy seq of partitions.  Returns a stateful
   transducer when no collection is provided.

Answer 1

这个特殊案例是briefly highlighted Rich Hickey 在他的演讲中说道:您不能将pipeline 与有状态转换器一起使用，这主要是因为pipeline 的并行性质。