/**
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.geowebcache.locks;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.commons.codec.digest.DigestUtils;
import org.geowebcache.GeoWebCacheException;
/**
* An in memory lock provider based on a striped lock
*
* @author Andrea Aime - GeoSolutions
*/
public class MemoryLockProvider implements LockProvider {
java.util.concurrent.locks.Lock[] locks;
public MemoryLockProvider() {
this(1024);
}
public MemoryLockProvider(int concurrency) {
locks = new java.util.concurrent.locks.Lock[concurrency];
for (int i = 0; i < locks.length; i++) {
locks[i] = new ReentrantLock();
}
}
public Lock getLock(String lockKey) {
final int idx = getIndex(lockKey);
locks[idx].lock();
return new Lock() {
boolean released = false;
public void release() throws GeoWebCacheException {
if(!released) {
released = true;
locks[idx].unlock();
}
}
};
}
private int getIndex(String lockKey) {
// Simply hashing the lock key generated a significant number of collisions,
// doing the SHA1 digest of it provides a much better distribution
int idx = Math.abs(DigestUtils.shaHex(lockKey).hashCode() % locks.length);
return idx;
}
}