Github user afs commented on the issue:
https://github.com/apache/jena/pull/297
From the documentation, the default mode of Surefire is that
`<threadCount>` is count-per-core.
{noformat}
perCoreThreadCount (Default: true)
(JUnit 4.7 provider) Indicates that threadCount, threadCountSuites,
threadCountClasses, threadCountMethods are per cpu core.
User property: perCoreThreadCount
{noformat}
So setting thread count to 50% CPUs is a number per core?
Let's go with the original PR for the 3.5.0 RC2.
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