In 2015, Google discovered a rare disastrous classloading bug in first call to LockSupport.park() that occurred in the AppClassLoader using the Java 7 ConcurrentHashMap, which used ReentrantLock for the synchronization.

Since then, the recommended fix for this bug seems to be this code snippet in any class that directly calls LockSupport.park():

static {
    // Prevent rare disastrous classloading in first call to LockSupport.park.
    // See: https://bugs.openjdk.java.net/browse/JDK-8074773
    Class<?> ensureLoaded = LockSupport.class;
}

Since the bug was logged, we have seen new classes in the JDK that call LockSupport.park(), but that do not have this code snippet. For example:

sun.nio.ch.Poller
jdk.internal.misc.ThreadFlock
java.util.concurrent.ThreadPerTaskExecutor

It should probably also be in:

java.util.concurrent.Exchanger

Considering how hard this bug is to detect and solve, it would probably be safer to add the code snippet into these newer classes.