tools.nrepl

Middleware linearization is nondeterministically wrong

Details

  • Type: Defect Defect
  • Status: Open Open
  • Priority: Critical Critical
  • Resolution: Unresolved
  • Affects Version/s: 0.2.3
  • Fix Version/s: None
  • Component/s: None
  • Labels:
    None
  • Environment:
    clojure 1.6.0

Description

I've had trouble getting my middleware ordered correctly, and have wittled it down to the following example which seems to only fail in some processes. I.e., it is deterministic within a particular jvm, but across jvms the result can change. My guess is that this has to do with hashing vars.

This code prints true (signifying a correct result) roughly 1/3 of the time and false otherwise.

(ns chas.core
  (:require [clojure.tools.nrepl.middleware :as mid]
            [clojure.tools.nrepl.middleware.pr-values]
            [clojure.tools.nrepl.middleware.session]))

(def wrap-foo identity)
(mid/set-descriptor! #'wrap-foo
                     {:expects #{#'clojure.tools.nrepl.middleware.session/session "eval"}})

(def wrap-bar identity)
(mid/set-descriptor! #'wrap-bar
                     {:requires #{#'clojure.tools.nrepl.middleware.session/session},
                      :expects #{"describe" #'clojure.tools.nrepl.middleware.pr-values/pr-values},
                      :handles {"stacktrace" {}}})

(defn -main
  []
  (println
   ;; should return true, since #'wrap-foo belongs later in the stack than
   ;; #'clojure.tools.nrepl.middleware.session/session due to its :expects
   ;; clause
   (->> [#'wrap-foo
         #'wrap-bar
         #'clojure.tools.nrepl.middleware.session/session]
        (mid/linearize-middleware-stack)
        (filter #{#'clojure.tools.nrepl.middleware.session/session #'wrap-foo})
        (= [#'clojure.tools.nrepl.middleware.session/session #'wrap-foo]))))

Activity

Gary Fredericks made changes -
Field Original Value New Value
Description I've had trouble getting my middleware ordered correctly, and have wittled it down to the following example which seems to only fail in some processes. I.e., it is deterministic within a particular jvm, but across jvms the result can change. My guess is that this has to do with hashing vars.

This code prints {{true}} (signifying a correct result) roughly 1/3 of the time and {{false}} otherwise.

{code}
(ns chas.core
  (:require [clojure.tools.nrepl.middleware :as mid]
            [clojure.tools.nrepl.middleware.pr-values]
            [clojure.tools.nrepl.middleware.session]))

(def wrap-foo identity)
(mid/set-descriptor! #'wrap-foo
                     {:expects #{#'clojure.tools.nrepl.middleware.session/session "eval"}})

(def wrap-bar identity)
(mid/set-descriptor! #'wrap-bar
                     {:requires #{#'clojure.tools.nrepl.middleware.session/session},
                      :expects #{"describe" #'clojure.tools.nrepl.middleware.pr-values/pr-values},
                      :handles {"stacktrace" {}}})

(defn -main
  []
  (println
   ;; should be true
   (= #'wrap-foo
      (last
       (mid/linearize-middleware-stack
        [#'wrap-foo
         #'wrap-bar
         #'clojure.tools.nrepl.middleware.session/session])))))
{code}
I've had trouble getting my middleware ordered correctly, and have wittled it down to the following example which seems to only fail in some processes. I.e., it is deterministic within a particular jvm, but across jvms the result can change. My guess is that this has to do with hashing vars.

This code prints {{true}} (signifying a correct result) roughly 1/3 of the time and {{false}} otherwise.

{code}
(ns chas.core
  (:require [clojure.tools.nrepl.middleware :as mid]
            [clojure.tools.nrepl.middleware.pr-values]
            [clojure.tools.nrepl.middleware.session]))

(def wrap-foo identity)
(mid/set-descriptor! #'wrap-foo
                     {:expects #{#'clojure.tools.nrepl.middleware.session/session "eval"}})

(def wrap-bar identity)
(mid/set-descriptor! #'wrap-bar
                     {:requires #{#'clojure.tools.nrepl.middleware.session/session},
                      :expects #{"describe" #'clojure.tools.nrepl.middleware.pr-values/pr-values},
                      :handles {"stacktrace" {}}})

(defn -main
  []
  (println
   ;; should return true, since #'wrap-foo belongs later in the stack than
   ;; #'clojure.tools.nrepl.middleware.session/session due to its :expects
   ;; clause
   (->> [#'wrap-foo
         #'wrap-bar
         #'clojure.tools.nrepl.middleware.session/session]
        (mid/linearize-middleware-stack)
        (filter #{#'clojure.tools.nrepl.middleware.session/session #'wrap-foo})
        (= [#'clojure.tools.nrepl.middleware.session/session #'wrap-foo]))))
{code}
Environment clojure 1.6.0
Affects Version/s 0.2.3 [ 10251 ]
Chas Emerick made changes -
Fix Version/s 0.2.4 [ 10160 ]
Chas Emerick made changes -
Fix Version/s 0.2.4 [ 10160 ]
Chas Emerick made changes -
Priority Major [ 3 ] Critical [ 2 ]
Gary Fredericks made changes -
Attachment NREPL-53.patch [ 13389 ]

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Dates

  • Created:
    Updated: