Looks like the patch attachment was stripped. I’ll include it inline:
—Ian
diff -r 3e9d813ff918 src/java.base/share/classes/jdk/internal/misc/Unsafe.java
--- a/src/java.base/share/classes/jdk/internal/misc/Unsafe.java Thu Aug 27
20:20:39 2020 +0200
+++ b/src/java.base/share/classes/jdk/internal/misc/Unsafe.java Fri Aug 28
15:21:01 2020 -0500
@@ -3412,9 +3412,8 @@
* Corresponds to C11 atomic_thread_fence(memory_order_acquire)
* (an "acquire fence").
*
- * A pure LoadLoad fence is not provided, since the addition of LoadStore
- * is almost always desired, and most current hardware instructions that
- * provide a LoadLoad barrier also provide a LoadStore barrier for free.
+ * Provides a LoadLoad barrier followed by a LoadStore barrier.
+ *
* @since 1.8
*/
@HotSpotIntrinsicCandidate
@@ -3427,9 +3426,8 @@
* Corresponds to C11 atomic_thread_fence(memory_order_release)
* (a "release fence").
*
- * A pure StoreStore fence is not provided, since the addition of LoadStore
- * is almost always desired, and most current hardware instructions that
- * provide a StoreStore barrier also provide a LoadStore barrier for free.
+ * Provides a StoreStore barrier followed by a LoadStore barrier.
+ *
* @since 1.8
*/
@HotSpotIntrinsicCandidate
@@ -3450,6 +3448,12 @@
/**
* Ensures that loads before the fence will not be reordered with
* loads after the fence.
+ *
+ * This method is operationally equivalent to {@link #loadFence()}
+ * as most hardware instructions that provide a LoadLoad barrier
+ * provide a LoadStore barrier for free.
+ *
+ * @since 9
*/
public final void loadLoadFence() {
loadFence();
@@ -3458,6 +3462,12 @@
/**
* Ensures that stores before the fence will not be reordered with
* stores after the fence.
+ *
+ * This method is operationally equivalent to {@link #storeFence()}
+ * as most hardware instructions that provide a StoreStore barrier
+ * provide a LoadStore barrier for free.
+ *
+ * @since 9
*/
public final void storeStoreFence() {
storeFence();
> On Aug 28, 2020, at 3:12 PM, Ian Graves <ian.gra...@oracle.com> wrote:
>
> Hello,
>
> When reviewing some of the documentation in jdk.internal.misc.Unsafe, it
> appears that there is some dated information regarding the availability of
> “pure barrier” methods (i.e. pure StoreStoreFence sans a LoadStore barrier).
> When the storeFence() and loadFence() methods were implemented the pure
> variations (loadLoadFence(), storeStoreFence()) were not implemented and the
> documentation indicated as much. This is no longer the case.
>
> I’ve included a patch with this email that updates the docs to reflect the
> new state of affairs here as well as indicate some implementation details as
> to how the pure variants utilize the impure original methods.
>
> Thanks!
>
> Ian
>
