ASYNC-271: Modified dispatch to work off of Executor instances instead of ExecutorService. Then, removed the use of newVTPertask... and implemented a reified Executor that defers to startVirtualThread instead. Modified relevant documentation to match changes.

Author: fogus

src/main/clojure/clojure/core/async.clj

@@ -17,11 +17,11 @@ go block threads - use Thread.setDefaultUncaughtExceptionHandler()
 to catch and handle.
 
 Use the Java system property `clojure.core.async.executor-factory`
-to specify a function that will provide ExecutorServices for
+to specify a function that will provide an Executor instance for
 application-wide use by core.async in lieu of its defaults. The
 property value should name a fully qualified var. The function
 will be passed a keyword indicating the context of use of the
-executor, and should return either an ExecutorService, or nil to
+executor, and should return either an Executor, or nil to
 use the default. Results per keyword will be cached and used for
 the remainder of the application. Possible context arguments are:
 
@@ -36,7 +36,7 @@ flow/process
 
 :core-async-dispatch - used for completion fn handling (e.g. in put!
 and take!, as well as go block IOC thunk processing) throughout
-core.async. If not supplied the ExecutorService for :io will be
+core.async. If not supplied, the Executor for :io will be
 used instead.
 
 The set of contexts may grow in the future so the function should

src/main/clojure/clojure/core/async/impl/dispatch.clj

@@ -8,7 +8,7 @@
 
 (ns ^{:skip-wiki true}
   clojure.core.async.impl.dispatch
-  (:import [java.util.concurrent Executors ExecutorService ThreadFactory]))
+  (:import [java.util.concurrent Executors Executor ExecutorService ThreadFactory]))
 
 (set! *warn-on-reflection* true)
 
@@ -120,8 +120,9 @@
 (defn- make-io-executor
   []
   (if vthreads-available-and-allowed?
-    (-> (.getDeclaredMethod Executors "newVirtualThreadPerTaskExecutor" (make-array Class 0))
-        (.invoke nil (make-array Class 0)))
+    (reify Executor
+      (execute [_ r]
+        (Thread/startVirtualThread r)))
     (make-ctp-named :io)))
 
 (defn ^:private create-default-executor
@@ -132,12 +133,12 @@
     :mixed   (make-ctp-named :mixed)))
 
 (def executor-for
-  "Given a workload tag, returns an ExecutorService instance and memoizes the result. By
+  "Given a workload tag, returns an Executor instance and memoizes the result. By
   default, core.async will defer to a user factory (if provided via sys prop) or construct
-  a specialized ExecutorService instance for each tag :io, :compute, and :mixed. When
+  a specialized Executor instance for each tag :io, :compute, and :mixed. When
   given the tag :core-async-dispatch it will default to the executor service for :io."
   (memoize
-   (fn ^ExecutorService [workload]
+   (fn ^Executor [workload]
      (let [sysprop-factory (when-let [esf (System/getProperty "clojure.core.async.executor-factory")]
                              (requiring-resolve (symbol esf)))
            sp-exec (and sysprop-factory (sysprop-factory workload))]
@@ -148,7 +149,7 @@
 
 (defn exec
   [^Runnable r workload]
-  (let [^ExecutorService e (executor-for workload)]
+  (let [^Executor e (executor-for workload)]
     (.execute e r)))
 
 (defn run