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From "Boris (JIRA)" <>
Subject [jira] Commented: (LANG-481) Possible race-conditions in hashCode of the range classes
Date Sat, 14 Nov 2009 15:33:39 GMT


Boris commented on LANG-481:

The current hashCode() is fine of course :) And as optimum long as speed is no concern it's
also the best. Just my 2ct on this topic:

Caching or pre-calculating the value will be a trade-off on how you want to use the class.
If you pre-calculate the value and never use hashCode() the "effort" was pointless. If you
cache it, it will MAY be re-calculated on every call (but this is rather unlikely).

I think the cached-approach is the best (if it's done right of course :)), but the constructor-approach
is easier to get right.
But as one can use String.hashCode() as a boilerplate it should be easy to implement optimistic
caching right.

> Possible race-conditions in hashCode of the range classes
> ---------------------------------------------------------
>                 Key: LANG-481
>                 URL:
>             Project: Commons Lang
>          Issue Type: Bug
>    Affects Versions: 2.4
>            Reporter: Boris
>            Priority: Minor
>             Fix For: 3.0
>         Attachments: LANG-481-reordering_datarace.patch, LANG-481.patch
> The hashCode() methods of the range classes look very suspicious to me. The value is
lazily initialized, but the calculation is done _on the cached value. With some unlucky timing
a caller may get an incomplete hash.
> An unlucky sequence of Code could be something like
> T1:        if (hashCode == 0) // true
> T1:            hashCode = 17;
> T2:         if (hashCode == 0) // now false because hashCode was already set to 17
> T2:         return hashCode; // return 17
> T1:            hashCode = 37 * hashCode...........
> where T1 and T2 are different threads accessing the method in parallel and T2 gets the
wrong hash "17".
> Affected classes are
> org.apache.commons.lang.math.DoubleRange
> org.apache.commons.lang.math.FloatRange
> org.apache.commons.lang.math.IntRange
> org.apache.commons.lang.math.LongRange
> org.apache.commons.lang.math.NumberRange
> org.apache.commons.lang.math.Range
> Possible fix: calculate the hash on a temporary variable and finally assign it to the

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