/*
* 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.Deque;
import java.util.LinkedList;
import java.util.List;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.pig.backend.hadoop.executionengine.physicalLayer.PigLogger;
import org.apache.pig.backend.hadoop.executionengine.physicalLayer.PigProgressable;
import org.apache.pig.builtin.OutputSchema;
import org.apache.pig.classification.InterfaceAudience;
import org.apache.pig.classification.InterfaceStability;
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.impl.util.UDFContext;
import org.apache.pig.impl.util.Utils;
import org.apache.pig.parser.ParserException;
/**
* The class is used to implement functions to be applied to
* fields in 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 exec() 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.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class EvalFunc<T> {
/**
* Reporter to send heartbeats to Hadoop. If exec will take more than a
* a few seconds {@link PigProgressable#progress} should be called
* occasionally to avoid timeouts. Default Hadoop timeout is 600 seconds.
*/
protected PigProgressable reporter;
/**
* Logging object. Log calls made on the front end will be sent to
* pig's log on the client. Log calls made on the backend will be
* sent to stdout and can be seen in the Hadoop logs.
*/
protected Log log = LogFactory.getLog(getClass());
/**
* Logger for aggregating warnings. Any warnings to be sent to the user
* should be logged to this via {@link PigLogger#warn}.
*/
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!=null && input.getAliases().size() > 0){
alias += input.getAliases().iterator().next() + "_";
}
alias += ++nextSchemaId;
return alias;
}
/**
* Return type of this instance of EvalFunc.
*/
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();
Deque<Type> geneticsStack = new LinkedList<Type>();
// Go up the hierachy of the class up to the EvalFunc
while (!superClass.isAssignableFrom(EvalFunc.class))
{
superType = superClass.getGenericSuperclass();
superClass = superClass.getSuperclass();
geneticsStack.push(superType);
}
// From EvalFunc (superclass), go downward (subclass),
// find the first class materialize the genetics
Type materializedType = null;
while (!geneticsStack.isEmpty()) {
Type aType = geneticsStack.pop();
if (aType instanceof ParameterizedType) {
// We materialized something, eg, materialized the type to Double,
// or materialized the type to Map<String, Object>, or materialized the type
// to T(another genetics). In the 1st case, getActualTypeArguments()
// returns a class, we can tell easily; In the 2nd and 3th case,
// getActualTypeArguments() returns a ParameterizedType,
// we cannot tell 2nd case from 3th case.
// So we need further check if the type inside materializedType
// are materialized (case 2)
materializedType = ((ParameterizedType)aType).getActualTypeArguments()[0];
}
Type currentType = materializedType;
while (currentType instanceof ParameterizedType)
currentType = ((ParameterizedType)currentType).getActualTypeArguments()[0];
if (currentType instanceof Class) {
returnType = materializedType;
break;
}
}
String errMsg = getClass() + "extends the raw type EvalFunc. It should extend the parameterized type EvalFunc<T> instead.";
if (returnType==null)
throw new RuntimeException(errMsg);
//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())).equals(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);
}
}
/**
* Get the Type that this EvalFunc returns.
* @return Type
*/
public Type getReturnType(){
return returnType;
}
// report that progress is being made (otherwise hadoop times out after 600 seconds working on one outer tuple)
/**
* Utility method to allow UDF to report progress. If exec will take more than a
* a few seconds {@link PigProgressable#progress} should be called
* occasionally to avoid timeouts. Default Hadoop timeout is 600 seconds.
*/
public final void progress() {
if (reporter != null) reporter.progress();
else warn("No reporter object provided to UDF.", PigWarning.PROGRESS_REPORTER_NOT_PROVIDED);
}
/**
* Issue a warning. Warning messages are aggregated and reported to
* the user.
* @param msg String message of the warning
* @param warningEnum type of warning
*/
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.
* Default implementation is a no-op.
*/
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;
/**
* Report the schema of the output of this UDF. Pig will make use of
* this in error checking, optimization, and planning. The schema
* of input data to this UDF is provided.
* <p>
* The default implementation interprets the {@link OutputSchema} annotation,
* if one is present. Otherwise, it returns <code>null</code> (no known output schema).
*
* @param input Schema of the input
* @return Schema of the output
*/
public Schema outputSchema(Schema input) {
OutputSchema schema = this.getClass().getAnnotation(OutputSchema.class);
try {
return (schema == null) ? null : Utils.getSchemaFromString(schema.value());
} catch (ParserException e) {
throw new RuntimeException(e);
}
}
/**
* 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.
*/
@Deprecated
public boolean isAsynchronous(){
return false;
}
public PigProgressable getReporter() {
return reporter;
}
/**
* Set the reporter. Called by Pig to provide a reference of
* the reporter to the UDF.
* @param reporter Hadoop reporter
*/
public final void setReporter(PigProgressable reporter) {
this.reporter = reporter;
}
/**
* Allow a UDF to specify type specific implementations of itself. For example,
* an implementation of arithmetic sum might have int and float implementations,
* since integer arithmetic performs much better than floating point arithmetic. Pig's
* typechecker will call this method and using the returned list plus the schema
* of the function's input data, decide which implementation of the UDF to use.
* @return A List containing FuncSpec objects representing the EvalFunc class
* which can handle the inputs corresponding to the schema in the objects. Each
* FuncSpec should be constructed with a schema that describes the input for that
* implementation. For example, the sum function above would return two elements in its
* list:
* <ol>
* <li>FuncSpec(this.getClass().getName(), new Schema(new Schema.FieldSchema(null, DataType.DOUBLE)))
* <li>FuncSpec(IntSum.getClass().getName(), new Schema(new Schema.FieldSchema(null, DataType.INTEGER)))
* </ol>
* This would indicate that the main implementation is used for doubles, and the special
* implementation IntSum is used for ints.
*/
public List<FuncSpec> getArgToFuncMapping() throws FrontendException{
return null;
}
/**
* Allow a UDF to specify a list of files it would like placed in the distributed
* cache. These files will be put in the cache for every job the UDF is used in.
* The default implementation returns null.
* @return A list of files
*/
public List<String> getCacheFiles() {
return null;
}
public PigLogger getPigLogger() {
return pigLogger;
}
/**
* Set the PigLogger object. Called by Pig to provide a reference
* to the UDF.
* @param pigLogger PigLogger object.
*/
public final void setPigLogger(PigLogger pigLogger) {
this.pigLogger = pigLogger;
}
public Log getLogger() {
return log;
}
private Schema inputSchemaInternal=null;
/**
* This method will be called by Pig both in the front end and back end to
* pass a unique signature to the {@link EvalFunc}. The signature can be used
* to store into the {@link UDFContext} any information which the
* {@link EvalFunc} needs to store between various method invocations in the
* front end and back end.
* @param signature a unique signature to identify this EvalFunc
*/
public void setUDFContextSignature(String signature) {
}
/**
* This method is for internal use. It is called by Pig core in both front-end
* and back-end to setup the right input schema for EvalFunc
*/
public void setInputSchema(Schema input){
this.inputSchemaInternal=input;
}
/**
* This method is intended to be called by the user in {@link EvalFunc} to get the input
* schema of the EvalFunc
*/
public Schema getInputSchema(){
return this.inputSchemaInternal;
}
}