有没有办法来评估Clojure的STM交易是否正在重试,以及以什么速度进行?
答案 0 :(得分:2)
您可以观察参考的history count
,表明存在争用:
user=> (def my-ref (ref 0 :min-history 1))
#'user/my-ref
user=> (ref-history-count my-ref)
0
user=> (dosync (alter my-ref inc))
1
user=> (ref-history-count my-ref)
1
历史记录计数不直接代表争用。相反,它表示为维护并发读取而维护的过去值的数量。
历史记录的大小受min
和max
值的限制。默认情况下,它们分别为0
和10
,但您可以在创建ref
时更改它们(请参见上文)。由于min-history
默认为0
,因此您通常不会看到ref-history-count
返回非零值,除非参考号存在争用。
在此处查看有关history count
的更多讨论:https://groups.google.com/forum/?fromgroups#!topic/clojure/n_MKCoa870o
我认为clojure.core
提供的任何方式都没有办法观察目前STM交易的速度。你当然可以做类似于@Chouser在history stress test中所做的事情:
(dosync
(swap! try-count inc)
...)
即。在交易中增加一个计数器。每次尝试交易时都会发生增量。如果try-count
大于1
,则会重试该交易。
答案 1 :(得分:2)
通过引入命名的dosync块和提交计数(命名的dosync成功的次数),可以很容易地跟踪线程重试给定事务的时间
(def ^{:doc "ThreadLocal<Map<TxName, Map<CommitNumber, TriesCount>>>"}
local-tries (let [l (ThreadLocal.)]
(.set l {})
l))
(def ^{:doc "Map<TxName, Int>"}
commit-number (ref {}))
(def history ^{:doc "Map<ThreadId, Map<TxName, Map<CommitNumber, TriesCount>>>"}
(atom {}))
(defn report [_ thread-id tries]
(swap! history assoc thread-id tries))
(def reporter (agent nil))
(defmacro dosync [tx-name & body]
`(clojure.core/dosync
(let [cno# (@commit-number ~tx-name 0)
tries# (update-in (.get local-tries) [~tx-name] update-in [cno#] (fnil inc 0))]
(.set local-tries tries#)
(send reporter report (.getId (Thread/currentThread)) tries#))
~@body
(alter commit-number update-in [~tx-name] (fnil inc 0))))
鉴于以下示例......
(def foo (ref {}))
(def bar (ref {}))
(defn x []
(dosync :x ;; `:x`: the tx-name.
(let [r (rand-int 2)]
(alter foo assoc r (rand))
(Thread/sleep (rand-int 400))
(alter bar assoc (rand-int 2) (@foo r)))))
(dotimes [i 4]
(future
(dotimes [i 10]
(x))))
... @history
评估为:
;; {thread-id {tx-name {commit-number tries-count}}}
{40 {:x {3 1, 2 4, 1 3, 0 1}}, 39 {:x {2 1, 1 3, 0 1}}, ...}
答案 2 :(得分:0)
这种额外的实施方式非常简单。
;; {thread-id retries-of-latest-tx}
(def tries (atom {}))
;; The max amount of tries any thread has performed
(def max-tries (atom 0))
(def ninc (fnil inc 0))
(def reporter (agent nil))
(defn report [_ tid]
(swap! max-tries #(max % (get @tries tid 0)))
(swap! tries update-in [tid] (constantly 0)))
(defmacro dosync [& body]
`(clojure.core/dosync
(swap! tries update-in [(.getId (Thread/currentThread))] ninc)
(commute commit-id inc)
(send reporter report (.getId (Thread/currentThread)))
~@body))