With VarHandles integrated into JDK 9, we now have the opportunity to use the actual Unsafe.weakCompareAndSet entry points in java.util.concurrent, not delegate them to stronger forms.

E.g.:

diff -r 195c39d24602 src/java.base/share/classes/java/util/concurrent/atomic/AtomicBoolean.java
--- a/src/java.base/share/classes/java/util/concurrent/atomic/AtomicBoolean.java Thu Apr 07 15:09:03 2016 +0800
+++ b/src/java.base/share/classes/java/util/concurrent/atomic/AtomicBoolean.java Thu Apr 07 11:10:51 2016 +0300
@@ -115,9 +115,9 @@
      * @return {@code true} if successful
      */
     public boolean weakCompareAndSet(boolean expect, boolean update) {
- return U.compareAndSwapInt(this, VALUE,
- (expect ? 1 : 0),
- (update ? 1 : 0));
+ return U.weakCompareAndSwapInt(this, VALUE,
+ (expect ? 1 : 0),
+ (update ? 1 : 0));
     }