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(ns ^{:author "Chas Emerick"}
(:require [ :as t]
(:use [ :only (response-for returning)]
[ :only (set-descriptor!)])
(:import clojure.lang.LineNumberingPushbackReader
( StringReader Writer)
(java.util.concurrent LinkedBlockingQueue
TimeUnit ThreadPoolExecutor
(def ^{:dynamic true
:doc "The message currently being evaluated."}
*msg* nil)
(defn evaluate
"Evaluates some code within the dynamic context defined by a map of `bindings`,
as per `clojure.core/get-thread-bindings`.
Uses `clojure.main/repl` to drive the evaluation of :code in a second
map argument (either a string or a seq of forms to be evaluated), which may
also optionally specify a :ns (resolved via `find-ns`). The map MUST
contain a Transport implementation in :transport; expression results and errors
will be sent via that Transport.
Returns the dynamic scope that remains after evaluating all expressions
in :code.
It is assumed that `bindings` already contains useful/appropriate entries
for all vars indicated by `clojure.main/with-bindings`."
[bindings {:keys [code ns transport] :as msg}]
(let [explicit-ns-binding (when-let [ns (and ns (-> ns symbol find-ns))]
{#'*ns* ns})
bindings (atom (merge bindings explicit-ns-binding))
out (@bindings #'*out*)
err (@bindings #'*err*)]
(if (and ns (not explicit-ns-binding))
(t/send transport (response-for msg {:status #{:error :namespace-not-found :done}}))
(with-bindings @bindings
;; clojure.main/repl paves over certain vars even if they're already thread-bound
:init #(do (set! *compile-path* (@bindings #'*compile-path*))
(set! *1 (@bindings #'*1))
(set! *2 (@bindings #'*2))
(set! *3 (@bindings #'*3))
(set! *e (@bindings #'*e)))
:read (if (string? code)
(let [reader (LineNumberingPushbackReader. (StringReader. code))]
#(read reader false %2))
(let [code (.iterator code)]
#(or (and (.hasNext code) (.next code)) %2)))
:prompt (fn [])
:need-prompt (constantly false)
; TODO pretty-print?
:print (fn [v]
(reset! bindings (assoc (get-thread-bindings)
#'*3 *2
#'*2 *1
#'*1 v))
(.flush ^Writer err)
(.flush ^Writer out)
(t/send transport (response-for msg
{:value v
:ns (-> *ns* ns-name str)})))
; TODO customizable exception prints
:caught (fn [e]
(let [root-ex (#'clojure.main/root-cause e)]
(when-not (instance? ThreadDeath root-ex)
(reset! bindings (assoc (get-thread-bindings) #'*e e))
(t/send transport (response-for msg {:status :eval-error
:ex (-> e class str)
:root-ex (-> root-ex class str)}))
(clojure.main/repl-caught e)))))
(.flush ^Writer out)
(.flush ^Writer err)))))
(defn- configure-thread-factory
"Returns a new ThreadFactory for the given session. This implementation
generates daemon threads, with names that include the session id."
(let [session-thread-counter (AtomicLong. 0)]
(reify ThreadFactory
(newThread [_ runnable]
(doto (Thread. runnable
(format "nREPL-worker-%s" (.getAndIncrement session-thread-counter)))
(.setDaemon true))))))
(def ^{:private true} jdk6? (try
(Class/forName "java.util.ServiceLoader")
(catch ClassNotFoundException e false)))
; this is essentially the same as Executors.newCachedThreadPool, except
; for the JDK 5/6 fix described below
(defn- configure-executor
"Returns a ThreadPoolExecutor, configured (by default) to
have no core threads, use an unbounded queue, create only daemon threads,
and allow unused threads to expire after 30s."
[& {:keys [keep-alive queue thread-factory]
:or {keep-alive 30000
queue (SynchronousQueue.)}}]
; ThreadPoolExecutor in JDK5 *will not run* submitted jobs if the core pool size is zero and
; the queue has not yet rejected a job (see
(ThreadPoolExecutor. (if jdk6? 0 1) Integer/MAX_VALUE
(long 30000) TimeUnit/MILLISECONDS
(or thread-factory (configure-thread-factory))))
; A little mini-agent implementation. Needed because agents cannot be used to host REPL
; evaluation:
(defn- prep-session
(locking session
(returning session
(when-not (-> session meta :queue)
(alter-meta! session assoc :queue (atom clojure.lang.PersistentQueue/EMPTY))))))
(declare run-next)
(defn- run-next*
[session executor]
(let [qa (-> session meta :queue)]
(loop []
(let [q @qa
qn (pop q)]
(if-not (compare-and-set! qa q qn)
(when (seq qn)
(.execute executor (run-next session executor (peek qn)))))))))
(defn- run-next
[session executor f]
(run-next* session executor))))
(defn- queue-eval
"Queues the function for the given session."
[session executor f]
(let [qa (-> session prep-session meta :queue)]
(loop []
(let [q @qa]
(if-not (compare-and-set! qa q (conj q f))
(when (empty? q)
(.execute executor (run-next session executor f))))))))
(defn interruptible-eval
"Evaluation middleware that supports interrupts. Returns a handler that supports
\"eval\" and \"interrupt\" :op-erations that delegates to the given handler
[h & {:keys [executor] :or {executor (configure-executor)}}]
(fn [{:keys [op session interrupt-id id transport] :as msg}]
(case op
(if-not (:code msg)
(t/send transport (response-for msg :status #{:error :no-code}))
(queue-eval session executor
(partial reset! session)
(fn []
(alter-meta! session assoc
:thread (Thread/currentThread)
:eval-msg msg)
(binding [*msg* msg]
(returning (dissoc (evaluate @session msg) #'*msg*)
(t/send transport (response-for msg :status :done))
(alter-meta! session dissoc :thread :eval-msg)))))))
; interrupts are inherently racy; we'll check the agent's :eval-msg's :id and
; bail if it's different than the one provided, but it's possible for
; that message's eval to finish and another to start before we send
; the interrupt / .stop.
(let [{:keys [id eval-msg ^Thread thread]} (meta session)]
(if (or (not interrupt-id)
(= interrupt-id (:id eval-msg)))
(if-not thread
(t/send transport (response-for msg :status #{:done :session-idle}))
; notify of the interrupted status before we .stop the thread so
; it is received before the standard :done status (thereby ensuring
; that is stays within the scope of a seq
(t/send transport {:status #{:interrupted}
:id (:id eval-msg)
:session id})
(.stop thread)
(t/send transport (response-for msg :status #{:done}))))
(t/send transport (response-for msg :status #{:error :interrupt-id-mismatch :done}))))
(h msg))))
(set-descriptor! #'interruptible-eval
{:requires #{"clone" "close" #'}
:expects #{}
:handles {"eval"
{:doc "Evaluates code."
:requires {"code" "The code to be evaluated."
"session" "The ID of the session within which to evaluate the code."}
:optional {"id" "An opaque message ID that will be included in responses related to the evaluation, and which may be used to restrict the scope of a later \"interrupt\" operation."}
:returns {}}
{:doc "Attempts to interrupt some code evaluation."
:requires {"session" "The ID of the session used to start the evaluation to be interrupted."}
:optional {"interrupt-id" "The opaque message ID sent with the original \"eval\" request."}
:returns {"status" "'interrupted' if an evaluation was identified and interruption will be attempted
'session-idle' if the session is not currently evaluating any code
'interrupt-id-mismatch' if the session is currently evaluating code sent using a different ID than specified by the \"interrupt-id\" value "}}}})
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