antville/helma
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Updated size of internal HashMap and rotation threshold to avoid

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rehashing to take place in internal maps.

Provided setCapacity() method to change cache capacity during runtime.
This commit is contained in:
hns 2002-09-17 22:43:19 +00:00
parent d4f379a54d
commit 2dda7607c5
1 changed files with 37 additions and 12 deletions
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41
src/helma/util/CacheMap.java
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@ -44,9 +44,6 @@ import java.util.HashMap;
public class CacheMap {
// Number of buckets.
private static final int nBuckets = 2;
// Load factor.
private float loadFactor;
@ -82,11 +79,17 @@ public class CacheMap {
if ( initialCapacity <= 0 || loadFactor <= 0.0 )
throw new IllegalArgumentException();
this.loadFactor = loadFactor;
threshold = (int) (initialCapacity * loadFactor) - 1;
eachCapacity = initialCapacity / nBuckets + 1;
oldTable = new HashMap (eachCapacity, loadFactor);
// table rotation threshold: we allow each table to gain
// initialCapacity/2 entries.
threshold = initialCapacity / 2;
// We deliberately choose the initial capacity of tables large
// enough that it can hold threshold entries without being rehashed,
// in other words, make sure our threshold for table rotation is lower
// than that of the underlying HashMap for table rehashing.
eachCapacity = (int) (threshold / loadFactor) + 2;
// create tables
oldTable = new HashMap ();
newTable = new HashMap (eachCapacity, loadFactor);
// System.out.println ("CREATED NEW CACHEMAP: CAP="+initialCapacity+" EACH="+eachCapacity+" THRES="+threshold);
}
/// Constructs a new, empty hashtable with the specified initial
@ -109,6 +112,28 @@ public class CacheMap {
}
/// Set the capacity of the CacheMap
public void setCapacity(int capacity) {
// table rotation threshold: we allow each table to gain
// initialCapacity/2 entries.
int newThreshold = capacity / 2;
if (newThreshold != threshold) {
if (logger != null)
logger.log ("Setting cache capacity to "+capacity);
updateThreshold (newThreshold);
}
}
private synchronized void updateThreshold (int newThreshold) {
threshold = newThreshold;
eachCapacity = (int) (threshold / loadFactor) + 2;
// if newtable is larger than threshold, rotate.
if (newTable.size() > threshold) {
oldTable = newTable;
newTable = new HashMap (eachCapacity, loadFactor);
}
}
/// Returns true if the specified object is an element of the hashtable.
// This operation is more expensive than the containsKey() method.
// @param value the value that we are looking for
@ -207,7 +232,7 @@ public class CacheMap {
if (oldValue != null)
oldTable.remove( key );
else {
if (newTable.size() >= eachCapacity) {
if (newTable.size() >= threshold) {
// Rotate the tables.
if (logger != null)
logger.log ("Rotating Cache tables at "+newTable.size()+"/"+oldTable.size()+" (new/old)");