Currently these tests are precluded from running in parallel due to being listed in exclusiveAccess.dirs in TEST.ROOT. There are a bunch of other Attach API related tests also listed in exclusiveAccess.dirs. Last year I filed JDK-8244765 to remove all of them from exclusiveAccess.dirs because it seemed to no longer be necessary after a number of bug fixes. At the time I was indeed able to run all these tests in parallel with no issue, and did so with changes in my local repo for an extended period of time, but just never got around to pushing the change. Now I'm getting back to working on JDK-8244765, and the jstatd tests are failing when removed from exclusiveAccess.dirs. What I usually see is the following when running sun/tools/jstatd/TestJstatdServer.java:

java.lang.Exception: There is already RMI registry on the default port: RegistryImpl_Stub[UnicastRef [liveRef: [endpoint:[100.104.98.168:1099](remote),objID:[0:0:0, 0]]]]
at JstatdTest.verifyNoRmiRegistryOnDefaultPort(JstatdTest.java:368)
at JstatdTest.runTest(JstatdTest.java:327)
at JstatdTest.doTest(JstatdTest.java:320)
at TestJstatdServer.main(TestJstatdServer.java:39)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
at java.base/java.lang.reflect.Method.invoke(Method.java:577)
at com.sun.javatest.regtest.agent.MainActionHelper$AgentVMRunnable.run(MainActionHelper.java:312)
at java.base/java.lang.Thread.run(Thread.java:833)

I'm not sure when this got introduced. I can't see any changes in the jstatd directory since I filed JDK-8244765 that may have contributed to this. In any case, due to this issue jstatd tests will remain on the exclusiveAccess.dirs list even after fixing JDK-8244765.