/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.pig;
import java.io.IOException;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.List;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.pig.data.Tuple;
import org.apache.pig.impl.PigContext;
import org.apache.pig.impl.logicalLayer.FrontendException;
import org.apache.pig.impl.logicalLayer.schema.Schema;
import org.apache.pig.backend.hadoop.executionengine.physicalLayer.PigLogger;
import org.apache.pig.backend.hadoop.executionengine.physicalLayer.PigProgressable;
/**
* The class is used to implement functions to be applied to
* a dataset. The function is applied to each Tuple in the set.
* The programmer should not make assumptions about state maintained
* between invocations of the invoke() method since the Pig runtime
* will schedule and localize invocations based on information provided
* at runtime. The programmer also should not make assumptions about when or
* how many times the class will be instantiated, since it may be instantiated
* multiple times in both the front and back end.
*/
public abstract class EvalFunc<T> {
// UDFs must use this to report progress
// if the exec is taking more that 300 ms
protected PigProgressable reporter;
protected Log log = LogFactory.getLog(getClass());
protected PigLogger pigLogger;
private static int nextSchemaId; // for assigning unique ids to UDF columns
protected String getSchemaName(String name, Schema input) {
String alias = name + "_";
if (input.getAliases().size() > 0){
alias += input.getAliases().iterator().next() + "_";
}
alias += ++nextSchemaId;
return alias;
}
protected Type returnType;
public EvalFunc(){
//Figure out what the return type is by following the object hierarchy upto the EvalFunc
Class<?> superClass = getClass();
Type superType = getClass();
while (!superClass.isAssignableFrom(EvalFunc.class)){
superType = superClass.getGenericSuperclass();
superClass = superClass.getSuperclass();
}
String errMsg = getClass() + "extends the raw type EvalFunc. It should extend the parameterized type EvalFunc<T> instead.";
if (!(superType instanceof ParameterizedType))
throw new RuntimeException(errMsg);
Type[] parameters = ((ParameterizedType)superType).getActualTypeArguments();
if (parameters.length != 1)
throw new RuntimeException(errMsg);
returnType = parameters[0];
//Type check the initial, intermediate, and final functions
if (this instanceof Algebraic){
Algebraic a = (Algebraic)this;
errMsg = "function of " + getClass().getName() + " is not of the expected type.";
if (getReturnTypeFromSpec(new FuncSpec(a.getInitial())) != Tuple.class)
throw new RuntimeException("Initial " + errMsg);
if (getReturnTypeFromSpec(new FuncSpec(a.getIntermed())) != Tuple.class)
throw new RuntimeException("Intermediate " + errMsg);
if (getReturnTypeFromSpec(new FuncSpec(a.getFinal())) != returnType)
throw new RuntimeException("Final " + errMsg);
}
}
private Type getReturnTypeFromSpec(FuncSpec funcSpec){
try{
return ((EvalFunc<?>)PigContext.instantiateFuncFromSpec(funcSpec)).getReturnType();
}catch (ClassCastException e){
throw new RuntimeException(funcSpec + " does not specify an eval func", e);
}
}
public Type getReturnType(){
return returnType;
}
// report that progress is being made (otherwise hadoop times out after 600 seconds working on one outer tuple)
public final void progress() {
if (reporter != null) reporter.progress();
else warn("No reporter object provided to UDF.", PigWarning.PROGRESS_REPORTER_NOT_PROVIDED);
}
public final void warn(String msg, Enum warningEnum) {
if(pigLogger != null) pigLogger.warn(this, msg, warningEnum);
else log.warn("No logger object provided to UDF: " + this.getClass().getName() + ". " + msg);
}
/**
* Placeholder for cleanup to be performed at the end. User defined functions can override.
*
*/
public void finish(){}
/**
* This callback method must be implemented by all subclasses. This
* is the method that will be invoked on every Tuple of a given dataset.
* Since the dataset may be divided up in a variety of ways the programmer
* should not make assumptions about state that is maintained between
* invocations of this method.
*
* @param input the Tuple to be processed.
* @return result, of type T.
* @throws IOException
*/
abstract public T exec(Tuple input) throws IOException;
/**
* @param input Schema of the input
* @return Schema of the output
*/
public Schema outputSchema(Schema input) {
return null;
}
/**
* This function should be overriden to return true for functions that return their values
* asynchronously. Currently pig never attempts to execute a function
* asynchronously.
* @return true if the function can be executed asynchronously.
*/
public boolean isAsynchronous(){
return false;
}
public PigProgressable getReporter() {
return reporter;
}
public final void setReporter(PigProgressable reporter) {
this.reporter = reporter;
}
/**
* @return A List containing FuncSpec objects representing the Function class
* which can handle the inputs corresponding to the schema in the objects
*/
public List<FuncSpec> getArgToFuncMapping() throws FrontendException{
return null;
}
public PigLogger getPigLogger() {
return pigLogger;
}
public final void setPigLogger(PigLogger pigLogger) {
this.pigLogger = pigLogger;
}
public Log getLogger() {
return log;
}
}