/***********************************************************************************************************************
* Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
*
* 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 eu.stratosphere.pact.runtime.task;
import eu.stratosphere.api.common.functions.Function;
/**
* The interface to be implemented by all pact drivers that run alone (or as the primary driver) in a nephele task.
* The driver is the code that deals with everything that specific to a certain PACT. It implements the actual
* <i>map</i> or <i>reduce</i> specific code.
*
* @see PactTaskContext
*
* @param <S> The type of stub driven by this driver.
* @param <OT> The data type of the records produced by this driver.
*/
public interface PactDriver<S extends Function, OT> {
void setup(PactTaskContext<S, OT> context);
/**
* Gets the number of inputs (= Nephele Gates and Readers) that the task has.
*
* @return The number of inputs.
*/
int getNumberOfInputs();
/**
* Gets the class of the stub type that is run by this task. For example, a <tt>MapTask</tt> should return
* <code>MapFunction.class</code>.
*
* @return The class of the stub type run by the task.
*/
Class<S> getStubType();
/**
* Flag indicating whether the inputs require always comparators or not.
*
* @return True, if the initialization should look for and create comparators, false otherwise.
*/
boolean requiresComparatorOnInput();
/**
* This method is called before the user code is opened. An exception thrown by this method
* signals failure of the task.
*
* @throws Exception Exceptions may be forwarded and signal task failure.
*/
void prepare() throws Exception;
/**
* The main operation method of the task. It should call the user code with the data subsets until
* the input is depleted.
*
* @throws Exception Any exception thrown by this method signals task failure. Because exceptions in the user
* code typically signal situations where this instance in unable to proceed, exceptions
* from the user code should be forwarded.
*/
void run() throws Exception;
/**
* This method is invoked in any case (clean termination and exception) at the end of the tasks operation.
*
* @throws Exception Exceptions may be forwarded.
*/
void cleanup() throws Exception;
/**
* This method is invoked when the driver must aborted in mid processing. It is invoked asynchronously by a different thread.
*
* @throws Exception Exceptions may be forwarded.
*/
void cancel() throws Exception;
}