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我为这篇文章的长度提前道歉。我花了相当多的时间缩短了时间，而且这个数字尽可能小。rxjava和clojure异步之谜：期货承诺和代理人，哦我的
我有一个谜，并会感激您的帮助。这个神秘来自我在Clojure写的一个rxjava observer的行为，这个行为来自于在线样本中的几个简单的observable。
一个observable同步地发送消息给其观察者的处理程序，并且我所谓的原则性观察者按预期行事。
另一个可观察的异步在另一个线程上通过Clojure future做同样的事情。完全相同的观察员不会捕获发布到其onNext的所有事件;它似乎在尾部丢失了随机数量的消息。
在等待promise和onCompleted的等待期满和等待发送到agent收集器的所有事件到期之间，存在故意竞赛。如果promise获胜，我希望看到false的onCompleted和agent中可能的短队列。如果agent获胜，我期望看到true的onCompleted和agent的队列中的所有消息。我不希望的结果是true对于onCompleted和从agent短队列。但是，墨菲不睡觉，这正是我所看到的。我不知道垃圾收集是否有问题，或者是一些内部排队到Clojure的STM，或者我的愚蠢，或者其他什么。
我按照自包含表单的顺序显示源代码，以便它可以通过lein repl直接运行。有三个cermonials脱身的办法：第一，leiningen项目文件，project.clj，这对0.9.0版Netflix的rxjava的声明依赖性：
(defproject expt2 "0.1.0-SNAPSHOT"
:description "FIXME: write description"
:url "http://example.com/FIXME"
:license {:name "Eclipse Public License"
:url "http://www.eclipse.org/legal/epl-v10.html"}
:dependencies [[org.clojure/clojure "1.5.1"]
[com.netflix.rxjava/rxjava-clojure "0.9.0"]]
:main expt2.core)
现在，命名空间和Clojure的要求和Java进口：
(ns expt2.core
(:require clojure.pprint)
(:refer-clojure :exclude [distinct])
(:import [rx Observable subscriptions.Subscriptions]))
最后，输出到控制台宏：
(defmacro pdump [x]
`(let [x# ~x]
(do (println "----------------")
(clojure.pprint/pprint '~x)
(println "~~>")
(clojure.pprint/pprint x#)
(println "----------------")
x#)))
最后，我的观察者。我使用agent来收集任何观察者的onNext发送的消息。我使用收集潜在的onError。我使用promise作为onCompleted，以便观察者外部的消费者可以等待它。
(defn- subscribe-collectors [obl]
(let [;; Keep a sequence of all values sent:
onNextCollector (agent [])
;; Only need one value if the observable errors out:
onErrorCollector (atom nil)
;; Use a promise for 'completed' so we can wait for it on
;; another thread:
onCompletedCollector (promise)]
(letfn [;; When observable sends a value, relay it to our agent"
(collect-next [item] (send onNextCollector (fn [state] (conj state item))))
;; If observable errors out, just set our exception;
(collect-error [excp] (reset! onErrorCollector excp))
;; When observable completes, deliver on the promise:
(collect-completed [ ] (deliver onCompletedCollector true))
;; In all cases, report out the back end with this:
(report-collectors [ ]
(pdump
;; Wait for everything that has been sent to the agent
;; to drain (presumably internal message queues):
{:onNext (do (await-for 1000 onNextCollector)
;; Then produce the results:
@onNextCollector)
;; If we ever saw an error, here it is:
:onError @onErrorCollector
;; Wait at most 1 second for the promise to complete;
;; if it does not complete, then produce 'false'.
;; I expect if this times out before the agent
;; times out to see an 'onCompleted' of 'false'.
:onCompleted (deref onCompletedCollector 1000 false)
}))]
;; Recognize that the observable 'obl' may run on another thread:
(-> obl
(.subscribe collect-next collect-error collect-completed))
;; Therefore, produce results that wait, with timeouts, on both
;; the completion event and on the draining of the (presumed)
;; message queue to the agent.
(report-collectors))))
现在，这里是一个同步观察。它沿着观察员的onNext喉咙抽25条消息，然后打电话给他们的onCompleted。
(defn- customObservableBlocking []
(Observable/create
(fn [observer] ; This is the 'subscribe' method.
;; Send 25 strings to the observer's onNext:
(doseq [x (range 25)]
(-> observer (.onNext (str "SynchedValue_" x))))
; After sending all values, complete the sequence:
(-> observer .onCompleted)
; return a NoOpSubsription since this blocks and thus
; can't be unsubscribed (disposed):
(Subscriptions/empty))))
我们订阅我们的观察员此观察到：
;;; The value of the following is the list of all 25 events:
(-> (customObservableBlocking)
(subscribe-collectors))
它能正常工作，而且我们看到控制台
{:onNext (do (await-for 1000 onNextCollector) @onNextCollector),
:onError @onErrorCollector,
:onCompleted (deref onCompletedCollector 1000 false)}
~~>
{:onNext
["SynchedValue_0"
"SynchedValue_1"
"SynchedValue_2"
"SynchedValue_3"
"SynchedValue_4"
"SynchedValue_5"
"SynchedValue_6"
"SynchedValue_7"
"SynchedValue_8"
"SynchedValue_9"
"SynchedValue_10"
"SynchedValue_11"
"SynchedValue_12"
"SynchedValue_13"
"SynchedValue_14"
"SynchedValue_15"
"SynchedValue_16"
"SynchedValue_17"
"SynchedValue_18"
"SynchedValue_19"
"SynchedValue_20"
"SynchedValue_21"
"SynchedValue_22"
"SynchedValue_23"
"SynchedValue_24"],
:onError nil,
:onCompleted true}
----------------
这里在随后的结果是一个异步观察到，做完全一样的东西，只有在future的线程上：
(defn- customObservableNonBlocking []
(Observable/create
(fn [observer] ; This is the 'subscribe' method
(let [f (future
;; On another thread, send 25 strings:
(doseq [x (range 25)]
(-> observer (.onNext (str "AsynchValue_" x))))
; After sending all values, complete the sequence:
(-> observer .onCompleted))]
; Return a disposable (unsubscribe) that cancels the future:
(Subscriptions/create #(future-cancel f))))))
;;; For unknown reasons, the following does not produce all 25 events:
(-> (customObservableNonBlocking)
(subscribe-collectors))
但是，惊喜，这里是我们在控制台上看到的：true为onCompleted，暗示promise DID NOT TIME-OUT;但只有一些异步信息。我们看到的实际消息数量因运行而异，这意味着有一些并发现象在发挥作用。线索表示赞赏。
----------------
{:onNext (do (await-for 1000 onNextCollector) @onNextCollector),
:onError @onErrorCollector,
:onCompleted (deref onCompletedCollector 1000 false)}
~~>
{:onNext
["AsynchValue_0"
"AsynchValue_1"
"AsynchValue_2"
"AsynchValue_3"
"AsynchValue_4"
"AsynchValue_5"
"AsynchValue_6"],
:onError nil,
:onCompleted true}
----------------
经过验证和测试。 –