1 files changed, 163 insertions, 0 deletions
diff --git a/trunk/infrastructure/net.appjet.common/util/ExpiringMapping.java b/trunk/infrastructure/net.appjet.common/util/ExpiringMapping.java
new file mode 100644
index 0000000..d4b9d5a
--- /dev/null
+++ b/trunk/infrastructure/net.appjet.common/util/ExpiringMapping.java
@@ -0,0 +1,163 @@
+/**
+ * Copyright 2009 Google Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.appjet.common.util;
+
+import java.util.*;
+
+// this class is synchronized
+
+public class ExpiringMapping<K,V> {
+
+  private Map<K,TimeStampedValue> keyToValue =
+    new HashMap<K,TimeStampedValue>();
+  private SortedMap<Long,K> timeToKey= new TreeMap<Long,K>();
+  
+  private long lastTimeStamp = 0;
+
+  private ExpiryPolicy policy;
+  
+  public ExpiringMapping(final long maxAgeMillis) {
+    this(new ExpiryPolicy() {
+        public boolean hasExpired(long timeStamp, long now, int rank) {
+          return now - timeStamp > maxAgeMillis;
+        }
+      });
+  }
+  
+  protected ExpiringMapping(ExpiryPolicy policy) {
+    this.policy = policy;
+  }
+  
+  public synchronized void clear() {
+    keyToValue.clear();
+    timeToKey.clear();
+  }
+  
+  public synchronized void put(K key, V value) {
+    TimeStampedValue old = keyToValue.get(key);
+    if (old != null) {
+      timeToKey.remove(old.getTimeStamp());
+    }
+    TimeStampedValue newVal = new TimeStampedValue(value);
+    keyToValue.put(key, newVal);
+    timeToKey.put(newVal.getTimeStamp(), key);
+    checkExpiry();
+  }
+
+  public synchronized void touch(K key) {
+    TimeStampedValue old = keyToValue.get(key);
+    if (old != null) {
+      put(key, old.getValue());
+    }
+  }
+  
+  public synchronized void remove(Object key) {
+    TimeStampedValue old = keyToValue.get(key);
+    if (old != null) {
+      keyToValue.remove(key);
+      timeToKey.remove(old.getTimeStamp());
+    }
+  }
+
+  // doesn't "touch" key or trigger expiry of expired items
+  public synchronized V get(Object key) {
+    if (keyToValue.containsKey(key)) {
+      return keyToValue.get(key).getValue();
+    } else {
+      return null;
+    }
+  }
+
+  public synchronized boolean containsKey(Object key) {
+    return keyToValue.containsKey(key);
+  }
+
+  public synchronized void checkExpiry() {
+    while (timeToKey.size() > 0) {
+      long oldestTime = timeToKey.firstKey();
+      if (hasExpired(oldestTime, timeToKey.size())) {
+        remove(timeToKey.get(oldestTime));
+      }
+      else {
+        break;
+      }
+    }
+  }
+
+  // lists keys in time order, oldest to newest
+  public synchronized List<K> listAllKeys() {
+    List<K> keyList = new java.util.ArrayList<K>(timeToKey.size());
+    for(Map.Entry<Long,K> entry : timeToKey.entrySet()) {
+      keyList.add(entry.getValue());
+    }
+    return Collections.unmodifiableList(keyList);
+  }
+  
+  // result must be monotonic
+  private boolean hasExpired(long time, int rank) {
+    return policy.hasExpired(time, System.currentTimeMillis(), rank);
+  }
+  
+  private long nowTimeStamp() {
+    // return "now", but unique
+    long now = System.currentTimeMillis();
+    if (now <= lastTimeStamp) {
+      now = lastTimeStamp+1;
+    }
+    lastTimeStamp = now;
+    return now;
+  }
+    
+  private class TimeStampedValue {
+    private final V value;
+    private long timeStamp;
+    private TimeStampedValue(V value) {
+      this(value, nowTimeStamp());
+    }
+    private TimeStampedValue(V value, long timeStamp) {
+      this.value = value; this.timeStamp = timeStamp;
+    }
+    public void setTimeStamp(long ts) {
+      timeStamp = ts;
+    }
+    public long getTimeStamp() {
+      return timeStamp;
+    }
+    public V getValue() {
+      return value;
+    }
+    public String toString() {
+      return "("+value+", "+new Date(timeStamp)+")";
+    }
+  }
+
+  public synchronized String toString() {
+    return keyToValue.toString();
+  }
+
+  protected interface ExpiryPolicy {
+    // result must be monotonic wrt timeStamp given now
+    boolean hasExpired(long timeStamp, long now, int rank);
+  }
+
+}
+
+  /*private static int compareLongs(long a, long b) {
+    if (a < b) return -1;
+    if (a > b) return 1;
+    return 0;
+    }*/