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/* Licensed 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.
 */
package org.flowable.cdi.spi;

import java.util.ServiceLoader;

import org.flowable.cdi.impl.FlowableCmmnExtension;
import org.flowable.cmmn.engine.CmmnEngine;

/**
 * 
 * Represents a strategy for building or looking up a {@link CmmnEngine}.
 * 
 * 
 * 
 * Implementations of this class are looked up using the Java SE 6 {@link ServiceLoader} facilities.
 * Users of this class that provide a custom implementation, must declare it in a file named
 * META-INF/services/org.flowable.cdi.spi.CmmnEngineLookup in order for it to be found.
 * 
 * 
 * 
 * Each implementation declares a "precedence".
 * The precedence controls the order in which the resolved implementations will be invoked. (See: getPrecedence().)
 * Implementations with a higher precedence will be invoked first.
 * 
 *
 * @author Andy Verberne
 * @since 6.6.1
 */
public interface CmmnEngineLookup {

    /**
     * Determines the ordering in which implementations are invoked.
     * Implementations with a high ordering are invoked first.
     */
    int getPrecedence();

    /**
     * This method will only be called once by the {@link FlowableCmmnExtension}, at startup
     * 
     * @return a {@link CmmnEngine}
     * 
     */
    CmmnEngine getCmmnEngine();

    /**
     * This method will only be called once by the {@link FlowableCmmnExtension}, at shutdown
     */
    void ungetCmmnEngine();
}