danlentz · February 18, 2014 05:19 · Feb 18, 2014
diff --git a/mmap.clj b/mmap.clj
@@ -0,0 +1,90 @@
+;   Copyright (c) Chris Houser, April 2008. All rights reserved.
+;   The use and distribution terms for this software are covered by the
+;   Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
+;   which can be found in the file epl-v10.html at the root of this distribution.
+;   By using this software in any fashion, you are agreeing to be bound by
+;   the terms of this license.
+;   You must not remove this notice, or any other, from this software.
+
+; Functions for memory-mapping files, plus some functions that use a
+; mmaped file for "normal" activies -- slurp, load-file, etc.
+
+(ns 
+  #^{:author "Chris Houser",
+     :doc "Functions for memory-mapping files, plus some functions that use a
+mmaped file for \"normal\" activies -- slurp, load-file, etc."}
+  clojure.contrib.mmap
+    (:refer-clojure :exclude (slurp load-file))
+    (:import (java.nio ByteBuffer CharBuffer)
+             (java.io PushbackReader InputStream InputStreamReader
+                      FileInputStream)))
+
+;(set! *warn-on-reflection* true)
+
+(def READ_ONLY #^{:private true}
+  (java.nio.channels.FileChannel$MapMode/READ_ONLY))
+
+(defn mmap
+  "Memory-map the file named f.  Returns a ByteBuffer."
+  [f]
+  (let [channel (.getChannel (FileInputStream. f))]
+    (.map channel READ_ONLY 0 (.size channel))))
+
+(defn slurp
+  "Reads the file named by f and returns it as a string."
+  [#^String f]
+  (.. java.nio.charset.Charset (forName "UTF-8")
+      (newDecoder) (decode (mmap f))))
+
+(defn buffer-stream
+  "Returns an InputStream for a ByteBuffer, such as returned by mmap."
+  [#^ByteBuffer buf]
+  (proxy [InputStream] []
+    (available [] (.remaining buf))
+    (read
+      ([] (if (.hasRemaining buf) (.get buf) -1))
+      ([dst offset len] (let [actlen (min (.remaining buf) len)]
+                          (.get buf dst offset actlen)
+                          (if (< actlen 1) -1 actlen))))))
+
+(defn load-file [f]
+  "Like clojure.lang/load-file, but uses mmap internally."
+  (with-open [rdr (-> f mmap buffer-stream InputStreamReader. PushbackReader.)]
+    (load-reader rdr)))
+
+
+(comment
+
+(alias 'mmap 'clojure.contrib.mmap)
+(alias 'core 'clojure.core)
+
+;---
+; zip_filter.clj is 95KB
+(def tf "/home/chouser/build/clojure/src/clj/clojure/core.clj")
+(println "\nload-file" tf)
+(time (dotimes [_ 5] (core/load-file tf))) ; 5420.177813 msecs
+(time (dotimes [_ 5] (mmap/load-file tf))) ; 7946.854434 msecs -- not so good
+
+;---
+; kern.log.0 is 961KB
+(def tf "/var/log/kern.log.0")
+(println "\nslurp" tf)
+(time (dotimes [_ 10] (.length (core/slurp tf)))) ; 435.767226 msecs
+(time (dotimes [_ 10] (.length (mmap/slurp tf)))) ;  93.176858 msecs
+
+;---
+; kern.log.0 is 961KB
+(def tf "/var/log/kern.log.0")
+(println "\nregex slurp large" tf)
+(time (dotimes [_ 10] (count (re-seq #"EXT3.*" (core/slurp tf))))) ; 416
+(time (dotimes [_ 10] (count (re-seq #"EXT3.*" (mmap/slurp tf))))) ; 101
+
+;---
+; mmap.clj is about 3.1KB
+(def tf "/home/chouser/proj/clojure-contrib/src/clojure/contrib/mmap.clj")
+(println "\nregex slurp small" tf)
+
+(time (dotimes [_ 1000] (count (re-seq #"defn \S*" (core/slurp tf))))) ; 308
+(time (dotimes [_ 1000] (count (re-seq #"defn \S*" (mmap/slurp tf))))) ; 198
+
+)