Make AtomicReferenceFieldUpdater fields static for [better performance](https://shipilev.net/blog/2015/faster-atomic-fu/#:~:text=thrown%20out%20of%20the%20window).

This may eliminate the reason for [an `Unsafe`-based implementation](#6806) even under Java 8, but we will ideally confirm that with benchmarks before ripping that implementation out. (There's also Android: `AtomicReferenceFieldUpdater` is available there, but we should look into performance, including under older versions, especially with AFAIK no plans to remove `Unsafe` there.)

(Also, make a few other tiny edits to the backport copy so that it matches the mainline copy more closely.)

RELNOTES=n/a
PiperOrigin-RevId: 713006636

Author: cpovirk

android/guava-tests/test/com/google/common/util/concurrent/AggregateFutureStateFallbackAtomicHelperTest.java

@@ -68,7 +68,13 @@ public static TestSuite suite() {
     // corresponding method on FuturesTest in the correct classloader.
     TestSuite suite = new TestSuite(AggregateFutureStateFallbackAtomicHelperTest.class.getName());
     for (Method method : FuturesTest.class.getDeclaredMethods()) {
-      if (Modifier.isPublic(method.getModifiers()) && method.getName().startsWith("test")) {
+      if (Modifier.isPublic(method.getModifiers())
+          && method.getName().startsWith("test")
+          /*
+           * When we block access to AtomicReferenceFieldUpdater, we can't even reflect on
+           * AbstractFuture, since it declares methods that use that type in their signatures.
+           */
+          && !method.getName().equals("testFutures_nullChecks")) {
         suite.addTest(
             TestSuite.createTest(
                 AggregateFutureStateFallbackAtomicHelperTest.class, method.getName()));

android/guava/src/com/google/common/util/concurrent/AbstractFuture.java

@@ -159,24 +159,15 @@ public final boolean cancel(boolean mayInterruptIfRunning) {
       helper = new UnsafeAtomicHelper();
     } catch (Exception | Error unsafeFailure) { // sneaky checked exception
       thrownUnsafeFailure = unsafeFailure;
-      // catch absolutely everything and fall through to our
-      // 'AtomicReferenceFieldUpdaterAtomicHelper' The access control checks that ARFU does means
-      // the caller class has to be AbstractFuture instead of
-      // AtomicReferenceFieldUpdaterAtomicHelper, so we annoyingly define these here
+      // Catch absolutely everything and fall through to AtomicReferenceFieldUpdaterAtomicHelper.
       try {
-        helper =
-            new AtomicReferenceFieldUpdaterAtomicHelper(
-                newUpdater(Waiter.class, Thread.class, "thread"),
-                newUpdater(Waiter.class, Waiter.class, "next"),
-                newUpdater(AbstractFuture.class, Waiter.class, "waiters"),
-                newUpdater(AbstractFuture.class, Listener.class, "listeners"),
-                newUpdater(AbstractFuture.class, Object.class, "value"));
+        helper = new AtomicReferenceFieldUpdaterAtomicHelper();
       } catch (Exception // sneaky checked exception
           | Error atomicReferenceFieldUpdaterFailure) {
         // Some Android 5.0.x Samsung devices have bugs in JDK reflection APIs that cause
         // getDeclaredField to throw a NoSuchFieldException when the field is definitely there.
-        // For these users fallback to a suboptimal implementation, based on synchronized. This will
-        // be a definite performance hit to those users.
+        // For these users fallback to a suboptimal implementation, based on synchronized. This
+        // will be a definite performance hit to those users.
         thrownAtomicReferenceFieldUpdaterFailure = atomicReferenceFieldUpdaterFailure;
         helper = new SynchronizedHelper();
       }
@@ -716,7 +707,7 @@ mayInterruptIfRunning, new CancellationException("Future.cancel() was called."))
    *
    * <p>The default implementation does nothing.
    *
-   * <p>This method is likely to be deprecated. Prefer to override {@link #afterDone}, consulting
+   * <p>This method is likely to be deprecated. Prefer to override {@link #afterDone}, checking
    * {@link #wasInterrupted} to decide whether to interrupt your task.
    *
    * @since 10.0
@@ -1447,24 +1438,16 @@ boolean casValue(AbstractFuture<?> future, @Nullable Object expect, Object updat
 
   /** {@link AtomicHelper} based on {@link AtomicReferenceFieldUpdater}. */
   private static final class AtomicReferenceFieldUpdaterAtomicHelper extends AtomicHelper {
-    final AtomicReferenceFieldUpdater<Waiter, Thread> waiterThreadUpdater;
-    final AtomicReferenceFieldUpdater<Waiter, Waiter> waiterNextUpdater;
-    final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Waiter> waitersUpdater;
-    final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Listener> listenersUpdater;
-    final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Object> valueUpdater;
-
-    AtomicReferenceFieldUpdaterAtomicHelper(
-        AtomicReferenceFieldUpdater<Waiter, Thread> waiterThreadUpdater,
-        AtomicReferenceFieldUpdater<Waiter, Waiter> waiterNextUpdater,
-        AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Waiter> waitersUpdater,
-        AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Listener> listenersUpdater,
-        AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Object> valueUpdater) {
-      this.waiterThreadUpdater = waiterThreadUpdater;
-      this.waiterNextUpdater = waiterNextUpdater;
-      this.waitersUpdater = waitersUpdater;
-      this.listenersUpdater = listenersUpdater;
-      this.valueUpdater = valueUpdater;
-    }
+    private static final AtomicReferenceFieldUpdater<Waiter, Thread> waiterThreadUpdater =
+        newUpdater(Waiter.class, Thread.class, "thread");
+    private static final AtomicReferenceFieldUpdater<Waiter, Waiter> waiterNextUpdater =
+        newUpdater(Waiter.class, Waiter.class, "next");
+    private static final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Waiter>
+        waitersUpdater = waitersUpdaterFromWithinAbstractFuture();
+    private static final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Listener>
+        listenersUpdater = listenersUpdaterFromWithinAbstractFuture();
+    private static final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Object>
+        valueUpdater = valueUpdaterFromWithinAbstractFuture();
 
     @Override
     void putThread(Waiter waiter, Thread newValue) {
@@ -1502,6 +1485,24 @@ boolean casValue(AbstractFuture<?> future, @Nullable Object expect, Object updat
     }
   }
 
+  /** Returns an {@link AtomicReferenceFieldUpdater} for {@link #waiters}. */
+  private static AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Waiter>
+      waitersUpdaterFromWithinAbstractFuture() {
+    return newUpdater(AbstractFuture.class, Waiter.class, "waiters");
+  }
+
+  /** Returns an {@link AtomicReferenceFieldUpdater} for {@link #listeners}. */
+  private static AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Listener>
+      listenersUpdaterFromWithinAbstractFuture() {
+    return newUpdater(AbstractFuture.class, Listener.class, "listeners");
+  }
+
+  /** Returns an {@link AtomicReferenceFieldUpdater} for {@link #value}. */
+  private static AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Object>
+      valueUpdaterFromWithinAbstractFuture() {
+    return newUpdater(AbstractFuture.class, Object.class, "value");
+  }
+
   /**
    * {@link AtomicHelper} based on {@code synchronized} and volatile writes.
    *

guava-tests/test/com/google/common/util/concurrent/AggregateFutureStateFallbackAtomicHelperTest.java

@@ -68,7 +68,13 @@ public static TestSuite suite() {
     // corresponding method on FuturesTest in the correct classloader.
     TestSuite suite = new TestSuite(AggregateFutureStateFallbackAtomicHelperTest.class.getName());
     for (Method method : FuturesTest.class.getDeclaredMethods()) {
-      if (Modifier.isPublic(method.getModifiers()) && method.getName().startsWith("test")) {
+      if (Modifier.isPublic(method.getModifiers())
+          && method.getName().startsWith("test")
+          /*
+           * When we block access to AtomicReferenceFieldUpdater, we can't even reflect on
+           * AbstractFuture, since it declares methods that use that type in their signatures.
+           */
+          && !method.getName().equals("testFutures_nullChecks")) {
         suite.addTest(
             TestSuite.createTest(
                 AggregateFutureStateFallbackAtomicHelperTest.class, method.getName()));

guava/src/com/google/common/util/concurrent/AbstractFuture.java

@@ -186,18 +186,9 @@ private static MethodHandles.Lookup methodHandlesLookupFromWithinAbstractFuture(
         helper = new UnsafeAtomicHelper();
       } catch (Exception | Error unsafeFailure) { // sneaky checked exception
         thrownUnsafeFailure = unsafeFailure;
-        // catch absolutely everything and fall through to our
-        // 'AtomicReferenceFieldUpdaterAtomicHelper' The access control checks that ARFU does means
-        // the caller class has to be AbstractFuture instead of
-        // AtomicReferenceFieldUpdaterAtomicHelper, so we annoyingly define these here
+        // Catch absolutely everything and fall through to AtomicReferenceFieldUpdaterAtomicHelper.
         try {
-          helper =
-              new AtomicReferenceFieldUpdaterAtomicHelper(
-                  newUpdater(Waiter.class, Thread.class, "thread"),
-                  newUpdater(Waiter.class, Waiter.class, "next"),
-                  newUpdater(AbstractFuture.class, Waiter.class, "waiters"),
-                  newUpdater(AbstractFuture.class, Listener.class, "listeners"),
-                  newUpdater(AbstractFuture.class, Object.class, "value"));
+          helper = new AtomicReferenceFieldUpdaterAtomicHelper();
         } catch (Exception // sneaky checked exception
             | Error atomicReferenceFieldUpdaterFailure) {
           // Some Android 5.0.x Samsung devices have bugs in JDK reflection APIs that cause
@@ -1559,24 +1550,16 @@ boolean casValue(AbstractFuture<?> future, @Nullable Object expect, Object updat
 
   /** {@link AtomicHelper} based on {@link AtomicReferenceFieldUpdater}. */
   private static final class AtomicReferenceFieldUpdaterAtomicHelper extends AtomicHelper {
-    final AtomicReferenceFieldUpdater<Waiter, Thread> waiterThreadUpdater;
-    final AtomicReferenceFieldUpdater<Waiter, Waiter> waiterNextUpdater;
-    final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Waiter> waitersUpdater;
-    final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Listener> listenersUpdater;
-    final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Object> valueUpdater;
-
-    AtomicReferenceFieldUpdaterAtomicHelper(
-        AtomicReferenceFieldUpdater<Waiter, Thread> waiterThreadUpdater,
-        AtomicReferenceFieldUpdater<Waiter, Waiter> waiterNextUpdater,
-        AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Waiter> waitersUpdater,
-        AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Listener> listenersUpdater,
-        AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Object> valueUpdater) {
-      this.waiterThreadUpdater = waiterThreadUpdater;
-      this.waiterNextUpdater = waiterNextUpdater;
-      this.waitersUpdater = waitersUpdater;
-      this.listenersUpdater = listenersUpdater;
-      this.valueUpdater = valueUpdater;
-    }
+    private static final AtomicReferenceFieldUpdater<Waiter, Thread> waiterThreadUpdater =
+        newUpdater(Waiter.class, Thread.class, "thread");
+    private static final AtomicReferenceFieldUpdater<Waiter, Waiter> waiterNextUpdater =
+        newUpdater(Waiter.class, Waiter.class, "next");
+    private static final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Waiter>
+        waitersUpdater = waitersUpdaterFromWithinAbstractFuture();
+    private static final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Listener>
+        listenersUpdater = listenersUpdaterFromWithinAbstractFuture();
+    private static final AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Object>
+        valueUpdater = valueUpdaterFromWithinAbstractFuture();
 
     @Override
     void putThread(Waiter waiter, Thread newValue) {
@@ -1614,6 +1597,24 @@ boolean casValue(AbstractFuture<?> future, @Nullable Object expect, Object updat
     }
   }
 
+  /** Returns an {@link AtomicReferenceFieldUpdater} for {@link #waiters}. */
+  private static AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Waiter>
+      waitersUpdaterFromWithinAbstractFuture() {
+    return newUpdater(AbstractFuture.class, Waiter.class, "waiters");
+  }
+
+  /** Returns an {@link AtomicReferenceFieldUpdater} for {@link #listeners}. */
+  private static AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Listener>
+      listenersUpdaterFromWithinAbstractFuture() {
+    return newUpdater(AbstractFuture.class, Listener.class, "listeners");
+  }
+
+  /** Returns an {@link AtomicReferenceFieldUpdater} for {@link #value}. */
+  private static AtomicReferenceFieldUpdater<? super AbstractFuture<?>, Object>
+      valueUpdaterFromWithinAbstractFuture() {
+    return newUpdater(AbstractFuture.class, Object.class, "value");
+  }
+
   /**
    * {@link AtomicHelper} based on {@code synchronized} and volatile writes.
    *