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/*
* Copyright Camunda Services GmbH and/or licensed to Camunda Services GmbH
* under one or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information regarding copyright
* ownership. Camunda licenses this file to you under the Apache License,
* Version 2.0; 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.camunda.bpm.engine.context;
import org.camunda.bpm.engine.impl.context.ProcessEngineContextImpl;
import java.util.concurrent.Callable;
/**
* When a Process Engine API call is performed, the engine
* will create a Process Engine Context. The context caches database
* entities, so that multiple operations on the same entity do not
* result in multiple database queries. This also means that the changes
* to these entities are accumulated and are flushed to the database
* as soon as the Process Engine API call returns (however, the current
* transaction might be committed at a later time).
*
* If a Process Engine API call is nested into another call, the
* default behaviour is to reuse the existing Process Engine Context.
* This means that the nested call will have access to the same cached
* entities and the changes made to them.
*
* When the nested call is to be executed in a new transaction, a new Process
* Engine Context needs to be created for its execution. In this case, the
* nested call will use a new cache for the database entities, independent of
* the previous (outer) call cache. This means that, the changes in the cache of
* one call are invisible to the other call and vice versa. When the nested call
* returns, the changes are flushed to the database independently of the Process
* Engine Context of the outer call.
*
* The ProcessEngineContext is a utility class to declare to
* the Process Engine that a new Process Engine Context needs to be created
* in order for the database operations in a nested Process Engine API call
* to be separated in a new transaction.
*
* Example on declaring a new Process Engine Context:
*
*
* try {
* ProcessEngineContext.requiresNew();
* runtimeService.startProcessInstanceByKey("EXAMPLE_INSTANCE");
* } finally {
* ProcessEngineContext.clear();
* }
*
*/
public class ProcessEngineContext {
/**
* Declares to the Process Engine that a new, separate context,
* bound to the current thread, needs to be created for all subsequent
* Process Engine database operations. The method should always be used
* in a try-finally block to ensure that {@link #clear()} is called
* under any circumstances.
*
* Please see the {@link ProcessEngineContext} class documentation for
* a more detailed description on the purpose of this method.
*/
public static void requiresNew() {
ProcessEngineContextImpl.set(true);
}
/**
* Declares to the Process Engine that the new Context created
* by the {@link #requiresNew()} method can be closed. Please
* see the {@link ProcessEngineContext} class documentation for
* a more detailed description on the purpose of this method.
*/
public static void clear() {
ProcessEngineContextImpl.clear();
}
/**
* Takes a callable and executes all engine API invocations
* within that callable in a new Process Engine Context. Please
* see the {@link ProcessEngineContext} class documentation for
* a more detailed description on the purpose of this method.
*
* An alternative to calling:
*
*
* try {
* requiresNew();
* callable.call();
* } finally {
* clear();
* }
*
*
* @param callable the callable to execute
* @return what is defined by the callable passed to the method
* @throws Exception
*/
public static T withNewProcessEngineContext(Callable callable) throws Exception {
try {
requiresNew();
return callable.call();
} finally {
clear();
}
}
}