RFR: 8260869: Test java/foreign/TestHandshake.java fails intermittently

[Maurizio Cimadamore]

This simple fix reduces the amount of concurrency on the foreign memory TestHandshake test. As this test spins a new accessor thread for each available processors, on machines which feature an high number of available processors (because of multi-threading), and which are slower in forking new threads (e.g. Windows), the test can sometimes timeout.

The sensible step, for now, is to introduce an hard limit on the number of concurrent accessor threads being created. I've looked at the test logs quite in depth, and there's nothing suggesting that something else is amiss - the number of concurrent threads just seem to be too high in some instances.

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Commit messages:
 - Reduce concurrency in handshake test

Changes: https://git.openjdk.java.net/jdk/pull/2748/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2748&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260869
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2748.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2748/head:pull/2748

PR: https://git.openjdk.java.net/jdk/pull/2748