FIFOCache


1   // Copyright (c) 2003-2007, Jodd Team (jodd.sf.net). All Rights Reserved.
2   
3   package jodd.cache;
4   
5   import java.util.LinkedHashMap  ;
6   import java.util.Iterator  ;
7   
8   /**
9    * FIFO (first in first out) cache.
10   *
11   * <p>
12   * FIFO (first in first out): just adds items to the cache as they are accessed, putting them in a queue or buffer and
13   * not changing their location in the buffer; when the cache is full, items are ejected in the order they were
14   * added. Cache access overhead is constant time regardless of the size of the cache. The advantage of this algorithm
15   * is that it's simple and fast; it can be implemented using a simple array and an index. The disadvantage is that
16   * it's not very smart; it doesn't make any effort to keep more commonly used items in cache.<br>
17   * Summary for FIFO: fast, not adaptive, not scan resistant
18   */
19  public class FIFOCache extends AbstractCacheMap {
20  
21      public FIFOCache(int cacheSize) {
22          this(cacheSize, 0);
23      }
24  
25      /**
26       * Creates a new LRU cache.
27       */
28      public FIFOCache(int cacheSize, long timeout) {
29          this.cacheSize = cacheSize;
30          this.timeout = timeout;
31          cacheMap = new LinkedHashMap  (cacheSize + 1, 1.0f, false);
32      }
33  
34  
35      // ---------------------------------------------------------------- prune
36  
37      /**
38       * Prune expired objects and, if cache is still full, the first one.
39       */
40      public synchronized int prune() {
41          int count = 0;
42          CacheObject first = null;
43          Iterator   values = cacheMap.values().iterator();
44          while (values.hasNext()) {
45              CacheObject co = (CacheObject) values.next();
46              if (co.isExpired() == true) {
47                  values.remove();
48                  count++;
49              }
50              if (first == null) {
51                  first = co;
52              }
53          }
54          if (isFull()) {
55              if (first != null) {
56                  cacheMap.remove(first.key);
57              }
58          }
59          return count;
60      }
61  }
62
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