Summary

Method LockSupport.setCurrentBlocker was added as part of JDK-8229442 mainly to allow implementations to maintain compatibility with tools and utilities reporting LockSupport.getBlocker when threads are parked.

Problem

The primary rationale for this method is to allow people to improve compatibility with previous implementations that includes calls to LockSupport.park, with respect to tools expecting a particular type of blocker object to be reported in stack traces etc.

Solution

LockSupport.setCurrentBlocker allows a given blocker to be set instead of per-park arguments for upcoming calls to park that may be performed in some other object.

Specification

/**
 * Sets the object to be returned by invocations of {@link
 * #getBlocker getBlocker} for the current thread. This method may
 * be used before invoking the no-argument version of {@link
 * LockSupport#park() park()} from non-public objects, allowing
 * more helpful diagnostics, or retaining compatibility with
 * previous implementations of blocking methods.  Previous values
 * of the blocker are not automatically restored after blocking.
 * To obtain the effects of {@code park(b}}, use {@code
 * setCurrentBlocker(b); park(); setCurrentBlocker(null);}
 *
 * @param blocker the blocker object
 * @since 14
 */
public static void setCurrentBlocker(Object blocker) {
    U.putObjectOpaque(Thread.currentThread(), PARKBLOCKER, blocker);
}