3:31 a.m.
[
https://issues.redhat.com/browse/DROOLS-1422?page=com.atlassian.jira.plug...
]
Mario Fusco updated DROOLS-1422:
--------------------------------
Sprint: 2020 Week 52-03 (from Dec 21)
Make AccumulateFunction interface simpler and more powerful
-----------------------------------------------------------
Key: DROOLS-1422
URL: https://issues.redhat.com/browse/DROOLS-1422
Project: Drools
Issue Type: Feature Request
Components: core engine
Reporter: Geoffrey De Smet
Assignee: Mario Fusco
Priority: Major
* Replace the AccumulateFunction interface with the AccumulateFunction2 interface:
** All core runtime code uses the AccumulateFunction2 interface.
** Deprecate AccumulateFunction and use a bridge class at DRL compilation time so old
implementations still work because they are bridged into the new interface
* Changes of the AccumulateFunction2:
** Methods no longer throw checked exceptions (no "throws Exception"), so
drools doesn't have to catch them. This might improve performance.
** Remove "Serializable context". The class itself contains the state.
*** Remove method createContext()
*** Replace method init(Serializeble) with constructor call (no-args normally)
*** Remove parameter Serializable from accumulate(value), reserve(value) and getResult()
methods
*** Instead of making 1 AccFunction instance and n context instances, make n AccFunction
instances. This uses less memory.
*** This might improve performance (data locality).
** It should Serializable, but doesn't have to Externalizable. Removes methods
writeExternal() and readExternal() in the user implementation.
* Interface ReversableAccumulateFunction2 extends AccumulateFunction2
** Only ReversableAccumulateFunction2 has method reverse(value)
** Remove method supportsReverse(): the custom accumulate is reverseable if it also
implements this interface
* Opportunities
** construction parameters. For example: fixed average for standard deviation (very
useful for OptaPlanner)
** Multi-argument accumulates, for example in DRL: `$total : standardDeviation($groupBy,
$weight)`
Notice how clean the user implementation would become.
{code}
// NEW
public class SumAccumulateFunction
implements ReversableAccumulateFunction2<Integer, Integer> {
public int total;
public SumAccumulateFunction() {
total = 0;
}
public void accumulate(Integer value) {
total += value;
}
public void reverse(Integer value) {
total -= value;
}
public Integer getResult() {
return total;
}
}
{code}
*Compare that with the old way:*
{code}
// OLD
public class SumAccumulateFunction implements AccumulateFunction {
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
}
public void writeExternal(ObjectOutput out) throws IOException { }
protected static class SumData implements Externalizable {
public double total = 0;
public SumData() {}
public void readExternal(ObjectInput in) throws IOException,
ClassNotFoundException {
total = in.readDouble();
}
public void writeExternal(ObjectOutput out) throws IOException {
out.writeDouble(total);
}
}
public Serializable createContext() {
return new SumData();
}
public void init(Serializable context) {
SumData data = (SumData) context;
data.total = 0;
}
public void accumulate(Serializable context,
Object value) {
SumData data = (SumData) context;
data.total += ((Number) value).doubleValue();
}
public void reverse(Serializable context,
Object value) {
SumData data = (SumData) context;
data.total -= ((Number) value).doubleValue();
}
public Object getResult(Serializable context) {
return ((SumData) context).total;
}
public boolean supportsReverse() {
return true;
}
public Class<?> getResultType() {
return Double.class;
}
}
{code}
Some other cases:
Different result type than value type:
{code}
public class AverageAccumulateFunction
implements ReversableAccumulateFunction2<Integer, Double> {
public int total;
public int count;
public AverageAccumulateFunction() {
total = 0;
count = 0;
}
public void accumulate(Integer value) {
total += value;
count++;
}
public void reverse(Integer value) {
total -= value;
count--;
}
public Double getResult() {
return (double) total / count;
}
}
{code}
Construction parameter:
{code}
public class StdDeviationAccumulateFunction
implements ReversableAccumulateFunction2<Integer, Double> {
public final double average;
public double variance;
public StdDeviationAccumulateFunction(double average) {
this.average = average;
variance = 0;
}
public void accumulate(double value) {
variance += (value - average)²; // TODO
}
public void reverse(double value) {
variance -= (value - average)²; // TODO
}
public Double getResult() {
return Math.sqrt(variance);
}
}
{code}
TODO multi-argument accumulate:
...
--
This message was sent by Atlassian Jira
(v8.13.1#813001)