/*
* Licensed to Crate under one or more contributor license agreements.
* See the NOTICE file distributed with this work for additional
* information regarding copyright ownership. Crate licenses this file
* to you under the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License. You may
* obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
* implied. See the License for the specific language governing
* permissions and limitations under the License.
*
* However, if you have executed another commercial license agreement
* with Crate these terms will supersede the license and you may use the
* software solely pursuant to the terms of the relevant commercial
* agreement.
*/
package io.crate.blob;
import org.elasticsearch.cluster.routing.Murmur3HashFunction;
import java.util.concurrent.Semaphore;
/**
* Offers coordination support for blob operations which need to execute in a mutually exclusive way
* (eg. blob commits for the same blob digest cannot execute concurrently)
*
* Should be used like this:
*
* <pre>
* Semaphore semaphore = blobCoordinator.digestCoordinator(digest);
* try {
* semaphore.acquire();
*
* try {
* // guaranteed single thread access to execute operation
* } finally {
* semaphore.release();
* }
* } catch(InterruptedException e) {
* // couldn't acquire semaphore
* }
* </pre>
*/
class BlobCoordinator {
private final Semaphore[] digestBinarySemaphores;
BlobCoordinator() {
digestBinarySemaphores = new Semaphore[500];
for (int i = 0; i < digestBinarySemaphores.length; i++) {
digestBinarySemaphores[i] = new Semaphore(1);
}
}
Semaphore digestCoordinator(String digest) {
return digestBinarySemaphores[Math.abs(Murmur3HashFunction.hash(digest) % digestBinarySemaphores.length)];
}
}