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https://issues.apache.org/jira/browse/RNG-72?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16781699#comment-16781699
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Alex D Herbert commented on RNG-72:
-----------------------------------
{quote}I think that synchronization is required within the "if (rng == null)"
to avoid a race condition.
{quote}
Yes. Good point.
I have in the past ignored this when using EnumMap to store stuff. Internally
it uses a fixed length array so you can add to it concurrently. But you risk
breaking the state of the EnumMap such as its known size. A race condition also
creates multiple types of the item you are storing of which only one will be
permanent and the others will end up being discarded. Sometimes this is OK.
However looking at the JDK source for creating a {{ThreadLocal<>}} it does some
magic with the thread table used to store the object which is most probably not
OK.
> Create a RandomSource.create benchmark
> --------------------------------------
>
> Key: RNG-72
> URL: https://issues.apache.org/jira/browse/RNG-72
> Project: Commons RNG
> Issue Type: New Feature
> Components: simple
> Affects Versions: 1.3
> Reporter: Alex D Herbert
> Assignee: Alex D Herbert
> Priority: Minor
> Labels: performance-benchmark
> Fix For: 1.3
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> The recommended method to construct a {{UniformRandomProvider}} is to use,
> e.g.:
> {code:java}
> import org.apache.commons.rng.UniformRandomProvider;
> import org.apache.commons.rng.simple.RandomSource;
> UniformRandomProvider rng = RandomSource.create(RandomSource.MWC_256);
> {code}
> The factory method knows the type of seed required for the constructor and
> generates one as appropriate.
> This factory method could be made more efficient, in particular:
> * Reducing synchronisation around the single source of random seed data
> * Adding knowledge of the required seed size for arrays
> * Changing internal data structures, e.g. {{Map<Class<?>,
> SeedConverter<?,?>>}} can be changed to {{Map<SeedType, SeedConverter<?,?>>}}
> using an {{EnumMap}} if a new enum {{SeedType}} was created for all the
> supported seeds (currently 4 types).
> * Add a new interface to replace {{SeedConverter<?,?>.convert()}} with a
> {{.convert(int outputArraySize)}} method to allow conversions to generate
> appropriately sized arrays. The parameter can be ignored for non-array
> conversions but could optimise array conversions.
> This ticket is to add a JMH benchmark to compare the speed of construction of
> all the providers using:
> * Their native constructor
> * {{RandomSource}} using the native seed of the correct size (calls a
> constructor using reflection)
> * {{RandomSource}} using a non native seed (requires seed conversion)
> * {{RandomSource}} using no seed (requires seed generation)
> The report will be posted here. It could be added to the user guide for
> reference.
> This work is motivated by the new {{XorShiRo}} generators in version 1.3 that
> have a native array seed size of 2, 4, or 8. The current {{RandomSource}}
> create method will generate a fixed seed of length 128 for seeding.
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