/***********************************************************************************************************************
* 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.api.common.functions;
import eu.stratosphere.configuration.Configuration;
/**
* An base interface for all user-defined functions. This class defines methods for
* the life cycle of the functions, as well as methods to access the context in which the functions
* are executed.
*/
public interface Function {
/**
* Initialization method for the function. It is called before the actual working methods
* (like <i>map</i> or <i>join</i>) and thus suitable for one time setup work. For functions that
* are part of an iteration, this method will be invoked at the beginning of each iteration superstep.
* <p>
* The configuration object passed to the function can be used for configuration and initialization.
* The configuration contains all parameters that were configured on the function in the program
* composition.
*
* <pre><blockquote>
* public class MyMapper extends FilterFunction<String> {
*
* private String searchString;
*
* public void open(Configuration parameters) {
* this.searchString = parameters.getString("foo");
* }
*
* public boolean filter(String value) {
* return value.equals(searchString);
* }
* }
* </blockquote></pre>
* <p>
* By default, this method does nothing.
*
* @param parameters The configuration containing the parameters attached to the contract.
*
* @throws Exception Implementations may forward exceptions, which are caught by the runtime. When the
* runtime catches an exception, it aborts the task and lets the fail-over logic
* decide whether to retry the task execution.
*
* @see eu.stratosphere.configuration.Configuration
*/
void open(Configuration parameters) throws Exception;
/**
* Teardown method for the user code. It is called after the last call to the main working methods
* (e.g. <i>map</i> or <i>join</i>). For functions that are part of an iteration, this method will
* be invoked after each iteration superstep.
* <p>
* This method can be used for clean up work.
*
* @throws Exception Implementations may forward exceptions, which are caught by the runtime. When the
* runtime catches an exception, it aborts the task and lets the fail-over logic
* decide whether to retry the task execution.
*/
void close() throws Exception;
/**
* Gets the context that contains information about the UDF's runtime.
*
* Context information are for example {@link eu.stratosphere.api.common.accumulators.Accumulator}s
* or the {@link eu.stratosphere.api.common.cache.DistributedCache}.
*
* @return The UDF's runtime context.
*/
RuntimeContext getRuntimeContext();
/**
* Sets the function's runtime context. Called by the framework when creating a parallel instance of the function.
*
* @param t The runtime context.
*/
void setRuntimeContext(RuntimeContext t);
}