Package com.couchbase.client.core.service.strategies

Source Code of com.couchbase.client.core.service.strategies.PartitionSelectionStrategy

/**
* Copyright (C) 2014 Couchbase, Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALING
* IN THE SOFTWARE.
*/
package com.couchbase.client.core.service.strategies;

import com.couchbase.client.core.endpoint.Endpoint;
import com.couchbase.client.core.message.CouchbaseRequest;
import com.couchbase.client.core.message.kv.BinaryRequest;
import com.couchbase.client.core.message.kv.GetBucketConfigRequest;
import com.couchbase.client.core.state.LifecycleState;

/**
* Selects the {@link Endpoint} based on the information enclosed in the {@link CouchbaseRequest}.
*
* This strategy can be used to "pin" certain requests to specific endpoints based on the supplied information. The
* current implementation uses this technique to tie ID-based {@link BinaryRequest}s to the same endpoint to enforce
* at least some amount of ordering guarantees.
*
* @author Michael Nitschinger
* @since 1.0
*/
public class PartitionSelectionStrategy implements SelectionStrategy {

    @Override
    public Endpoint select(final CouchbaseRequest request, final Endpoint[] endpoints) {
        int numEndpoints = endpoints.length;
        if (numEndpoints == 0) {
            return null;
        }

        if (request instanceof BinaryRequest) {
            if (request instanceof GetBucketConfigRequest) {
                return selectFirstConnected(endpoints);
            } else {
                BinaryRequest binaryRequest = (BinaryRequest) request;
                short partition = binaryRequest.partition();
                if (partition > 0) {
                    int id = partition % numEndpoints;
                    Endpoint endpoint = endpoints[id];
                    if (endpoint != null && endpoint.isState(LifecycleState.CONNECTED)) {
                        return endpoint;
                    }
                } else {
                    return selectFirstConnected(endpoints);
                }
            }
        } else {
            throw new IllegalStateException("The PartitionSelectionStrategy does not understand: " + request);
        }

        return null;
    }

    /**
     * Helper method to select the first connected endpoint if no particular pinning is needed.
     *
     * @param endpoints the list of endpoints.
     * @return the first connected or null if none found.
     */
    private static final Endpoint selectFirstConnected(final Endpoint[] endpoints) {
        for (Endpoint endpoint : endpoints) {
            if (endpoint.isState(LifecycleState.CONNECTED)) {
                return endpoint;
            }
        }
        return null;
    }
}
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