org.infinispan.util.StripedHashFunction Maven / Gradle / Ivy
package org.infinispan.util;
import org.infinispan.commons.equivalence.Equivalence;
/**
* An hash function for stripping.
*
* It calculates the number of segments based on the concurrency level desired and hashes the object to the
* corresponding segments.
*
* @author Pedro Ruivo
* @since 8.0
*/
public class StripedHashFunction {
private final Equivalence equivalence;
private final int lockSegmentMask;
private final int lockSegmentShift;
private final int numSegments;
public StripedHashFunction(Equivalence equivalence, int concurrencyLevel) {
this.equivalence = equivalence;
int tempLockSegShift = 0;
int tmpNumSegments = 1;
while (tmpNumSegments < concurrencyLevel) {
++tempLockSegShift;
tmpNumSegments <<= 1;
}
lockSegmentShift = 32 - tempLockSegShift;
lockSegmentMask = tmpNumSegments - 1;
numSegments = tmpNumSegments;
}
/**
* @param hashCode the object's hash code serving as a key.
* @return the hash code of the key
*/
private static int hash(int hashCode) {
int h = hashCode;
h += ~(h << 9);
h ^= (h >>> 14);
h += (h << 4);
h ^= (h >>> 10);
return h;
}
/**
* @return the number of segments.
*/
public final int getNumSegments() {
return numSegments;
}
/**
* It calculates the segment in which the object belongs.
*
* @param object the object to hash.
* @return the segment index, between 0 and {@link #getNumSegments()}-1.
*/
public final int hashToSegment(T object) {
return (hash(equivalence.hashCode(object)) >>> lockSegmentShift) & lockSegmentMask;
}
}