Change directory structure.

[dvibrowser/dvi2epub.git] / src / main / java / jp / sourceforge / dvibrowser / dvicore / util / concurrent / CachedComputer.java

diff --git a/src/main/java/jp/sourceforge/dvibrowser/dvicore/util/concurrent/CachedComputer.java b/src/main/java/jp/sourceforge/dvibrowser/dvicore/util/concurrent/CachedComputer.java
new file mode 100644 (file)
index 0000000..9923d28
--- /dev/null
+++ b/src/main/java/jp/sourceforge/dvibrowser/dvicore/util/concurrent/CachedComputer.java
@@ -0,0 +1,143 @@
+/*
+ * Copyright (c) 2009, Takeyuki Nagao
+ * All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the
+ * following conditions are met:
+ * 
+ *  * Redistributions of source code must retain the above
+ *    copyright notice, this list of conditions and the
+ *    following disclaimer.
+ *  * Redistributions in binary form must reproduce the above
+ *    copyright notice, this list of conditions and the
+ *    following disclaimer in the documentation and/or other
+ *    materials provided with the distribution.
+ *    
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+ * USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
+ * OF SUCH DAMAGE.
+ */
+
+package jp.sourceforge.dvibrowser.dvicore.util.concurrent;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.concurrent.Future;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import jp.sourceforge.dvibrowser.dvicore.util.DviUtils;
+
+
+
+public class CachedComputer<K, V> implements Computer<K, V>
+{
+  private final class LinkedHashMapExtension extends
+      LinkedHashMap<K, CacheEntry<K, V>> {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    protected boolean removeEldestEntry(Map.Entry<K,CacheEntry<K, V>> eldest)
+    {
+      boolean doRemove = CachedComputer.this.removeEldestEntry(eldest);
+      LOGGER.finer("doRemove = " + doRemove);
+      return doRemove;
+    }
+  }
+
+  private static final Logger LOGGER = Logger.getLogger(CachedComputer.class.getName());
+  private final Map<K, CacheEntry<K, V>> map;
+  private final Computer<K, V> computer;
+  
+  public CachedComputer(final Computer<K, V> computer)
+  {
+    this.computer = computer;
+    map = Collections.synchronizedMap(createCache());
+  }
+  
+  protected Map<K, CacheEntry<K, V>> createCache()
+  {
+    return new LinkedHashMapExtension();
+  }
+  
+  protected boolean removeEldestEntry(Map.Entry<K, CacheEntry<K, V>> entry)
+  {
+    return false;
+  }
+  
+  protected synchronized Future<V> startComputation(final Computation<K, V> computable)
+  {
+    final Future<V> future = computer.compute(new Computation<K, V>() {
+      public V call() throws Exception {
+        try {
+          return computable.call();
+        } catch (Throwable e) {
+          // We would like to associate any exception with the return value of null.
+          DviUtils.logStackTrace(LOGGER, Level.SEVERE, e);
+          return null;
+        }
+      }
+
+      public K getCacheKey() {
+        return computable.getCacheKey();
+      }
+      
+    });
+    return future;
+  }
+
+  /* (non-Javadoc)
+   * @see Computer#compute(Computation, java.util.concurrent.ExecutorService)
+   */
+  public synchronized Future<V> compute(Computation<K, V> computable)
+  {
+    K key = computable.getCacheKey();
+    if (key == null) {
+      LOGGER.finer("Key is null: " + computable);
+      final Future<V> future = startComputation(computable);
+      return future;
+    }
+    CacheEntry<K, V> cacheEntry = map.get(key);
+    if (cacheEntry == null) {
+      LOGGER.finer("Cache miss: " + key);
+      final Future<V> future = startComputation(computable);
+      cacheEntry = new CacheEntry<K, V>(this, computable, future);
+      getCache().put(key, cacheEntry);
+      LOGGER.finer("Wrote cache: key=" + key + " value=" + future);
+    } else {
+      LOGGER.finest("Cache hit: " + key);
+    }
+    return cacheEntry.getFuture();
+  }
+
+  public synchronized Future<V> getCachedResult(Computation<K, V> computable)
+  {
+    K key = computable.getCacheKey();
+    if (key == null) {
+      return null;
+    }
+    CacheEntry<K, V> cacheEntry = map.get(key);
+    if (cacheEntry == null) {
+      return null;
+    } else {
+      return cacheEntry.getFuture();
+    }
+  }
+  
+  public Map<K, CacheEntry<K, V>> getCache()
+  {
+    return map;
+  }
+}