added more future fns, fixed print of pending futures, added promise/deliver

Author: richhickey

src/clj/clojure/core.clj

@@ -4023,6 +4023,14 @@
 
   Defaults to true")
 
+(defn future?
+  "Returns true if x is a future"
+  [x] (instance? java.util.concurrent.Future x))
+
+(defn future-done?
+  "Returns true if future f is done"
+  [#^java.util.concurrent.Future f] (.isDone f))
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; helper files ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 (alter-meta! (find-ns 'clojure.core) assoc :doc "Fundamental library of the Clojure language")
 (load "core_proxy")
@@ -4052,6 +4060,15 @@
   not yet finished, calls to deref/@ will block."  
   [& body] `(future-call (fn [] ~@body)))
 
+
+(defn future-cancel
+  "Cancels the future, if possible."
+  [#^java.util.concurrent.Future f] (.cancel f true))
+
+(defn future-cancelled?
+  "Returns true if future f is cancelled"
+  [#^java.util.concurrent.Future f] (.isCancelled f))
+
 (defn pmap
   "Like map, except f is applied in parallel. Semi-lazy in that the
   parallel computation stays ahead of the consumption, but doesn't
@@ -4131,3 +4148,28 @@
          (str "-" q))
        (when (:interim *clojure-version*)
          "-SNAPSHOT")))
+
+(defn promise
+  "Experimental.
+  Returns a promise object that can be read with deref/@, and set,
+  once only, with deliver. Calls to deref/@ prior to delivery will
+  block. All subsequent derefs will return the same delivered value
+  without blocking."  
+  []
+  (let [d (java.util.concurrent.CountDownLatch. 1)
+        v (atom nil)]
+    (proxy [clojure.lang.AFn clojure.lang.IDeref] []
+      (deref [] (.await d) @v)
+      (invoke [x]
+        (locking d
+          (if (pos? (.getCount d))
+            (do (.countDown d)
+                (reset! v x)
+                this)
+            (throw (IllegalStateException. "Multiple deliver calls to a promise"))))))))
+
+(defn deliver
+  "Experimental.
+  Delivers the supplied value to the promise, releasing any pending
+  derefs. A subsequent call to deliver on a promise will throw an exception."  
+  [promise val] (promise val))

src/clj/clojure/core_print.clj

@@ -312,6 +312,6 @@
   (print-sequential (format "#<%s@%x: "
                             (.getSimpleName (class o))
                             (System/identityHashCode o))
-                    pr-on, "", ">", (list @o), w))
+                    pr-on, "", ">", (list (if (and (future? o) (not (future-done? o))) :pending @o)), w))
 
 (def #^{:private true} print-initialized true)