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package org.apache.naming.resources;
import java.util.HashMap;
import java.util.Random;
/**
* Implements a special purpose cache.
*
* @author <a href="mailto:remm@apache.org">Remy Maucherat</a>
* @version $Revision: 1.4 $
*/
public class ResourceCache {
// ----------------------------------------------------------- Constructors
public ResourceCache() {
}
// ----------------------------------------------------- Instance Variables
/**
* Random generator used to determine elements to free.
*/
protected Random random = new Random();
/**
* Cache.
* Path -> Cache entry.
*/
protected CacheEntry[] cache = new CacheEntry[0];
/**
* Not found cache.
*/
protected HashMap notFoundCache = new HashMap();
/**
* Max size of resources which will have their content cached.
*/
protected int cacheMaxSize = 10240; // 10 MB
/**
* Max amount of removals during a make space.
*/
protected int maxAllocateIterations = 20;
/**
* Entry hit ratio at which an entry will never be removed from the cache.
* Compared with entry.access / hitsCount
*/
protected long desiredEntryAccessRatio = 3;
/**
* Spare amount of not found entries.
*/
protected int spareNotFoundEntries = 500;
/**
* Current cache size in KB.
*/
protected int cacheSize = 0;
/**
* Number of accesses to the cache.
*/
protected long accessCount = 0;
/**
* Number of cache hits.
*/
protected long hitsCount = 0;
// ------------------------------------------------------------- Properties
/**
* Return the access count.
* Note: Update is not synced, so the number may not be completely
* accurate.
*/
public long getAccessCount() {
return accessCount;
}
/**
* Return the maximum size of the cache in KB.
*/
public int getCacheMaxSize() {
return cacheMaxSize;
}
/**
* Set the maximum size of the cache in KB.
*/
public void setCacheMaxSize(int cacheMaxSize) {
this.cacheMaxSize = cacheMaxSize;
}
/**
* Return the current cache size in KB.
*/
public int getCacheSize() {
return cacheSize;
}
/**
* Return desired entry access ratio.
*/
public long getDesiredEntryAccessRatio() {
return desiredEntryAccessRatio;
}
/**
* Set the desired entry access ratio.
*/
public void setDesiredEntryAccessRatio(long desiredEntryAccessRatio) {
this.desiredEntryAccessRatio = desiredEntryAccessRatio;
}
/**
* Return the number of cache hits.
* Note: Update is not synced, so the number may not be completely
* accurate.
*/
public long getHitsCount() {
return hitsCount;
}
/**
* Return the maximum amount of iterations during a space allocation.
*/
public int getMaxAllocateIterations() {
return maxAllocateIterations;
}
/**
* Set the maximum amount of iterations during a space allocation.
*/
public void setMaxAllocateIterations(int maxAllocateIterations) {
this.maxAllocateIterations = maxAllocateIterations;
}
/**
* Return the amount of spare not found entries.
*/
public int getSpareNotFoundEntries() {
return spareNotFoundEntries;
}
/**
* Set the amount of spare not found entries.
*/
public void setSpareNotFoundEntries(int spareNotFoundEntries) {
this.spareNotFoundEntries = spareNotFoundEntries;
}
// --------------------------------------------------------- Public Methods
public boolean allocate(int space) {
int toFree = space - (cacheMaxSize - cacheSize);
if (toFree <= 0) {
return true;
}
// Increase the amount to free so that allocate won't have to run right
// away again
toFree += (cacheMaxSize / 20);
int size = notFoundCache.size();
if (size > spareNotFoundEntries) {
notFoundCache.clear();
cacheSize -= size;
toFree -= size;
}
if (toFree <= 0) {
return true;
}
int attempts = 0;
int entriesFound = 0;
long totalSpace = 0;
int[] toRemove = new int[maxAllocateIterations];
while (toFree > 0) {
if (attempts == maxAllocateIterations) {
// Give up, no changes are made to the current cache
return false;
}
if (toFree > 0) {
// Randomly select an entry in the array
int entryPos = -1;
boolean unique = false;
int count = 0;
while (!unique) {
unique = true;
entryPos = random.nextInt(cache.length) ;
// Guarantee uniqueness
for (int i = 0; i < entriesFound; i++) {
if (toRemove[i] == entryPos) {
unique = false;
}
}
}
long entryAccessRatio =
((cache[entryPos].accessCount * 100) / accessCount);
if (entryAccessRatio < desiredEntryAccessRatio) {
toRemove[entriesFound] = entryPos;
totalSpace += cache[entryPos].size;
toFree -= cache[entryPos].size;
entriesFound++;
}
}
attempts++;
}
// Now remove the selected entries
java.util.Arrays.sort(toRemove, 0, entriesFound);
CacheEntry[] newCache = new CacheEntry[cache.length - entriesFound];
int pos = 0;
int n = -1;
if (entriesFound > 0) {
n = toRemove[0];
for (int i = 0; i < cache.length; i++) {
if (i == n) {
if ((pos + 1) < entriesFound) {
n = toRemove[pos + 1];
pos++;
} else {
pos++;
n = -1;
}
} else {
newCache[i - pos] = cache[i];
}
}
}
cache = newCache;
cacheSize -= totalSpace;
return true;
}
public CacheEntry lookup(String name) {
CacheEntry cacheEntry = null;
accessCount++;
int pos = find(cache, name);
if ((pos != -1) && (name.equals(cache[pos].name))) {
cacheEntry = cache[pos];
}
if (cacheEntry == null) {
try {
cacheEntry = (CacheEntry) notFoundCache.get(name);
} catch (Exception e) {
// Ignore: the reliability of this lookup is not critical
}
}
if (cacheEntry != null) {
hitsCount++;
}
return cacheEntry;
}
public void load(CacheEntry entry) {
if (entry.exists) {
if (insertCache(entry)) {
cacheSize += entry.size;
}
} else {
int sizeIncrement = (notFoundCache.get(entry.name) == null) ? 1 : 0;
notFoundCache.put(entry.name, entry);
cacheSize += sizeIncrement;
}
}
public boolean unload(String name) {
CacheEntry removedEntry = removeCache(name);
if (removedEntry != null) {
cacheSize -= removedEntry.size;
return true;
} else if (notFoundCache.remove(name) != null) {
cacheSize--;
return true;
}
return false;
}
/**
* Find a map elemnt given its name in a sorted array of map elements.
* This will return the index for the closest inferior or equal item in the
* given array.
*/
private static final int find(CacheEntry[] map, String name) {
int a = 0;
int b = map.length - 1;
// Special cases: -1 and 0
if (b == -1) {
return -1;
}
if (name.compareTo(map[0].name) < 0) {
return -1;
}
if (b == 0) {
return 0;
}
int i = 0;
while (true) {
i = (b + a) / 2;
int result = name.compareTo(map[i].name);
if (result > 0) {
a = i;
} else if (result == 0) {
return i;
} else {
b = i;
}
if ((b - a) == 1) {
int result2 = name.compareTo(map[b].name);
if (result2 < 0) {
return a;
} else {
return b;
}
}
}
}
/**
* Insert into the right place in a sorted MapElement array, and prevent
* duplicates.
*/
private final boolean insertCache(CacheEntry newElement) {
CacheEntry[] oldCache = cache;
int pos = find(oldCache, newElement.name);
if ((pos != -1) && (newElement.name.equals(oldCache[pos].name))) {
return false;
}
CacheEntry[] newCache = new CacheEntry[cache.length + 1];
System.arraycopy(oldCache, 0, newCache, 0, pos + 1);
newCache[pos + 1] = newElement;
System.arraycopy
(oldCache, pos + 1, newCache, pos + 2, oldCache.length - pos - 1);
cache = newCache;
return true;
}
/**
* Insert into the right place in a sorted MapElement array.
*/
private final CacheEntry removeCache(String name) {
CacheEntry[] oldCache = cache;
int pos = find(oldCache, name);
if ((pos != -1) && (name.equals(oldCache[pos].name))) {
CacheEntry[] newCache = new CacheEntry[cache.length - 1];
System.arraycopy(oldCache, 0, newCache, 0, pos);
System.arraycopy(oldCache, pos + 1, newCache, pos,
oldCache.length - pos - 1);
cache = newCache;
return oldCache[pos];
}
return null;
}
}
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