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From sebb <seb...@gmail.com>
Subject Re: svn commit: r1197626 - /commons/proper/math/trunk/src/main/java/org/apache/commons/math/random/RandomDataImpl.java
Date Fri, 04 Nov 2011 17:50:38 GMT
On 4 November 2011 17:44, Phil Steitz <phil.steitz@gmail.com> wrote:
> On 11/4/11 10:25 AM, sebb wrote:
>> On 4 November 2011 16:20,  <psteitz@apache.org> wrote:
>>> Author: psteitz
>>> Date: Fri Nov  4 16:20:05 2011
>>> New Revision: 1197626
>>>
>>> URL: http://svn.apache.org/viewvc?rev=1197626&view=rev
>>> Log:
>>> Changed default non-secure generator to Well19937c and changed default seeds
to add system identity haschode to timestamp.  JIRA: MATH-701.
>> You've actually use the object hashcode - did you mean to use
>> j.l.System.indentityHashcode() ?
>
> Yes, maybe I am wrong, but I thought that's what you got by default
> when hashcode is not overridden.  What we want is just something
> that will be unique by instance (with high probability) and is
> relatively fast to compute.

Yes, you do get that if it is not overridden, but if the hashcode is
later overriden then:
- the Javadoc will not be accurate
- it may not be as quick to compute.

It would be easy to overlook this in a future update, so I'd recommend
using what the Javadoc says.

> Phil
>>
>>> Modified:
>>>    commons/proper/math/trunk/src/main/java/org/apache/commons/math/random/RandomDataImpl.java
>>>
>>> Modified: commons/proper/math/trunk/src/main/java/org/apache/commons/math/random/RandomDataImpl.java
>>> URL: http://svn.apache.org/viewvc/commons/proper/math/trunk/src/main/java/org/apache/commons/math/random/RandomDataImpl.java?rev=1197626&r1=1197625&r2=1197626&view=diff
>>> ==============================================================================
>>> --- commons/proper/math/trunk/src/main/java/org/apache/commons/math/random/RandomDataImpl.java
(original)
>>> +++ commons/proper/math/trunk/src/main/java/org/apache/commons/math/random/RandomDataImpl.java
Fri Nov  4 16:20:05 2011
>>> @@ -49,7 +49,7 @@ import org.apache.commons.math.util.Resi
>>>  * instance to generate non-secure data and a {@link java.security.SecureRandom}
>>>  * instance to provide data for the <code>nextSecureXxx</code> methods.
If no
>>>  * <code>RandomGenerator</code> is provided in the constructor,
the default is
>>> - * to use a generator based on {@link java.util.Random}. To plug in a different
>>> + * to use a {@link Well19937c} generator. To plug in a different
>>>  * implementation, either implement <code>RandomGenerator</code>
directly or
>>>  * extend {@link AbstractRandomGenerator}.
>>>  * <p>
>>> @@ -81,10 +81,10 @@ import org.apache.commons.math.util.Resi
>>>  * When a new <code>RandomDataImpl</code> is created, the underlying
random
>>>  * number generators are <strong>not</strong> initialized. If you
do not
>>>  * explicitly seed the default non-secure generator, it is seeded with the
>>> - * current time in milliseconds on first use. The same holds for the secure
>>> - * generator. If you provide a <code>RandomGenerator</code> to the
constructor,
>>> - * however, this generator is not reseeded by the constructor nor is it reseeded
>>> - * on first use.</li>
>>> + * current time in milliseconds plus the system identity hash code on first
use.
>>> + * The same holds for the secure generator. If you provide a <code>RandomGenerator</code>
>>> + * to the constructor, however, this generator is not reseeded by the constructor
>>> + * nor is it reseeded on first use.</li>
>>>  * <li>
>>>  * The <code>reSeed</code> and <code>reSeedSecure</code>
methods delegate to the
>>>  * corresponding methods on the underlying <code>RandomGenerator</code>
and
>>> @@ -827,7 +827,8 @@ public class RandomDataImpl implements R
>>>     /**
>>>      * Returns the RandomGenerator used to generate non-secure random data.
>>>      * <p>
>>> -     * Creates and initializes a default generator if null.
>>> +     * Creates and initializes a default generator if null. Uses a {@link
Well19937c}
>>> +     * generator with {@code System.currentTimeMillis() + hashCode()} as the
default seed.
>>>      * </p>
>>>      *
>>>      * @return the Random used to generate random data
>>> @@ -835,8 +836,7 @@ public class RandomDataImpl implements R
>>>      */
>>>     private RandomGenerator getRan() {
>>>         if (rand == null) {
>>> -            rand = new JDKRandomGenerator();
>>> -            rand.setSeed(System.currentTimeMillis());
>>> +            rand = new Well19937c(System.currentTimeMillis() + hashCode());
>>>         }
>>>         return rand;
>>>     }
>>> @@ -844,7 +844,8 @@ public class RandomDataImpl implements R
>>>     /**
>>>      * Returns the SecureRandom used to generate secure random data.
>>>      * <p>
>>> -     * Creates and initializes if null.
>>> +     * Creates and initializes if null.  Uses
>>> +     * {@code System.currentTimeMillis() + hashCode()} as the default seed.
>>>      * </p>
>>>      *
>>>      * @return the SecureRandom used to generate secure random data
>>> @@ -852,7 +853,7 @@ public class RandomDataImpl implements R
>>>     private SecureRandom getSecRan() {
>>>         if (secRand == null) {
>>>             secRand = new SecureRandom();
>>> -            secRand.setSeed(System.currentTimeMillis());
>>> +            secRand.setSeed(System.currentTimeMillis() + hashCode());
>>>         }
>>>         return secRand;
>>>     }
>>>
>>>
>>>
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>
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