Re: Better RecursiveTask Example

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Please go ahead and use it :-)

On Wed, 24 Nov 2021 at 22:42, Doug Lea via Concurrency-interest <
[email protected]> wrote:

>
> On 11/24/21 2:15 PM, Dr Heinz M. Kabutz via Concurrency-interest wrote:
> > Every time I see the example in RecursiveTask I have to cringe:
>
> The initial rationale was that "nearly everyone" knows Fibonacci so it
> doesn't need much explanation it. but you are right that even more
> people know factorial, and the BigInteger version fits RecursiveTask
> without needing caveats, so we should use it; thanks. Here's a javadoc'd
> version of your example. Any objections to using it?
>
>
>   *
>   * <pre> {@code
>   * public class FactorialTask extends RecursiveTask<BigInteger> {
>   *   private final int from, to;
>   *   public FactorialTask(int n) { this(0, n); }
>   *   private FactorialTask(int from, int to) { this.from = from;
> this.to = to; }
>   *   protected BigInteger compute() {
>   *     if (from == to)                        // base case
>   *       return (from == 0) ? BigInteger.ONE : BigInteger.valueOf(from);
>   *     int mid = (from + to) >>> 1;           // split in half
>   *     FactorialTask leftTask = (new FactorialTask(from, mid)).fork();
>   *     FactorialTask rightTask = new FactorialTask(mid + 1, to);
>   *     BigInteger right = rightTask.invoke(); // perform half the work
> locally
>   *     BigInteger left = leftTask.join();
>   *     return left.multiply(right);
>   *   }
>   * }}</pre>
>   *
>
> _______________________________________________
> Concurrency-interest mailing list
> [email protected]
> http://cs.oswego.edu/mailman/listinfo/concurrency-interest
>
-- 
Dr Heinz M. Kabutz (PhD CompSci)
Author of "The Java(tm) Specialists' Newsletter"
Sun/Oracle Java Champion
JavaOne Rockstar Speaker
http://www.javaspecialists.eu
Tel: +30 69 75 595 262
Skype: kabutz

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<div dir=3D"auto">Please go ahead and use it :-)</div><div><br><div class=
=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Wed, 24 Nov 2021 =
at 22:42, Doug Lea via Concurrency-interest &lt;<a href=3D"mailto:concurren=
[email protected]">[email protected]</a>&gt; wrote=
:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;bor=
der-left:1px #ccc solid;padding-left:1ex"><br>
On 11/24/21 2:15 PM, Dr Heinz M. Kabutz via Concurrency-interest wrote:<br>
&gt; Every time I see the example in RecursiveTask I have to cringe:<br>
<br>
The initial rationale was that &quot;nearly everyone&quot; knows Fibonacci =
so it <br>
doesn&#39;t need much explanation it. but you are right that even more <br>
people know factorial, and the BigInteger version fits RecursiveTask <br>
without needing caveats, so we should use it; thanks. Here&#39;s a javadoc&=
#39;d <br>
version of your example. Any objections to using it?<br>
<br>
<br>
=C2=A0=C2=A0*<br>
=C2=A0=C2=A0* &lt;pre&gt; {@code<br>
=C2=A0=C2=A0* public class FactorialTask extends RecursiveTask&lt;BigIntege=
r&gt; {<br>
=C2=A0=C2=A0*=C2=A0=C2=A0 private final int from, to;<br>
=C2=A0=C2=A0*=C2=A0=C2=A0 public FactorialTask(int n) { this(0, n); }<br>
=C2=A0=C2=A0*=C2=A0=C2=A0 private FactorialTask(int from, int to) { this.fr=
om =3D from; <br>
<a href=3D"http://this.to" rel=3D"noreferrer" target=3D"_blank">this.to</a>=
 =3D to; }<br>
=C2=A0=C2=A0*=C2=A0=C2=A0 protected BigInteger compute() {<br>
=C2=A0=C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0 if (from =3D=3D to)=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 // base case<br>
=C2=A0=C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return (from =3D=3D 0) ? =
BigInteger.ONE : BigInteger.valueOf(from);<br>
=C2=A0=C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0 int mid =3D (from + to) &gt;&gt;&gt; =
1;=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 // split in =
half<br>
=C2=A0=C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0 FactorialTask leftTask =3D (new Facto=
rialTask(from, mid)).fork();<br>
=C2=A0=C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0 FactorialTask rightTask =3D new Facto=
rialTask(mid + 1, to);<br>
=C2=A0=C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0 BigInteger right =3D rightTask.invoke=
(); // perform half the work <br>
locally<br>
=C2=A0=C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0 BigInteger left =3D leftTask.join();<=
br>
=C2=A0=C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0 return left.multiply(right);<br>
=C2=A0=C2=A0*=C2=A0=C2=A0 }<br>
=C2=A0=C2=A0* }}&lt;/pre&gt;<br>
=C2=A0=C2=A0*<br>
<br>
_______________________________________________<br>
Concurrency-interest mailing list<br>
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[email protected]</a><br>
<a href=3D"http://cs.oswego.edu/mailman/listinfo/concurrency-interest" rel=
=3D"noreferrer" target=3D"_blank">http://cs.oswego.edu/mailman/listinfo/con=
currency-interest</a><br>
</blockquote></div></div>-- <br><div dir=3D"ltr" class=3D"gmail_signature" =
data-smartmail=3D"gmail_signature">Dr Heinz M. Kabutz (PhD CompSci)<br>Auth=
or of &quot;The Java(tm) Specialists&#39; Newsletter&quot;<br>Sun/Oracle Ja=
va Champion<br>JavaOne Rockstar Speaker<br><a href=3D"http://www.javaspecia=
lists.eu" target=3D"_blank">http://www.javaspecialists.eu</a><br>Tel: +30 6=
9 75 595 262<br>Skype: kabutz<br></div>

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