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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-1134) unsafe initialization in BicubicSplineInterpolatingFunction
Date Tue, 01 Jul 2014 17:56:24 GMT

    [ https://issues.apache.org/jira/browse/MATH-1134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14049121#comment-14049121
] 

Gilles commented on MATH-1134:
------------------------------

0) is a bit sad, because it can be thread-safe in an obvious way (all fields "final").

Affirming thread-safety with 1) might not be as obvious. If only the "private" method that
computed the derivatives were "synchronized", there might still be race conditions (leading
to multiple computations of the same fields). While having all accessors synchronized will
bring a penalty to applications that really make concurrent accesses.

2) is not efficient, always (if derivatives are used).

3) is not efficient, at instantiation.

bq. Gilles suggestion to make 3) itself configurable sort of combines 3) and 0)

Yes, IIUC what you means by "combines".
Users who need the derivatives would have to specifically request that derivatives are computed
(at instantiation), while the default would leave them at "null" (and if called later a NPE
will be raised, by the JVM).
\[This is my preferred option. And you didn't rank it ;)\]

Another option might be to deprecate the derivatives code altogether. And perhaps move it
to a subclass. And reimplement it, using the "o.a.c.m.analysis.differentiation.DerivativeStructure".


> unsafe initialization in BicubicSplineInterpolatingFunction
> -----------------------------------------------------------
>
>                 Key: MATH-1134
>                 URL: https://issues.apache.org/jira/browse/MATH-1134
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.3
>            Reporter: Derek Scherger
>            Priority: Minor
>
> The lazy initialization of the internal array of partialDerivatives in BicubicSplineInterpolatingFunction
is not thread safe. If multiple threads call any of the partialDerivative functions concurrently
one thread may start the initialization and others will see the array is non-null and assume
it is fully initialized. If the internal array of partial derivatives was initialized in the
constructor this would not be a problem.
> i.e. the following check in partialDerivative(which, x, y)
>         if (partialDerivatives == null) {
>             computePartialDerivatives();
>         }
> will start the initialization. However in computePartialDerivatives()
>         partialDerivatives = new BivariateFunction[5][lastI][lastJ];
> makes it appear to other threads as the the initialization has completed when it may
not have.



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