--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/lang/invoke/SwitchPoint.java Wed Mar 23 23:02:31 2011 -0700
@@ -0,0 +1,199 @@
+/*
+ * Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang.invoke;
+
+/**
+ * <p>
+ * A {@code SwitchPoint} is an object which can publish state transitions to other threads.
+ * A switch point is initially in the <em>valid</em> state, but may at any time be
+ * changed to the <em>invalid</em> state. Invalidation cannot be reversed.
+ * A switch point can combine a <em>guarded pair</em> of method handles into a
+ * <em>guarded delegator</em>.
+ * The guarded delegator is a method handle which delegates to one of the old method handles.
+ * The state of the switch point determines which of the two gets the delegation.
+ * <p>
+ * A single switch point may be used to control any number of method handles.
+ * (Indirectly, therefore, it can control any number of call sites.)
+ * This is done by using the single switch point as a factory for combining
+ * any number of guarded method handle pairs into guarded delegators.
+ * <p>
+ * When a guarded delegator is created from a guarded pair, the pair
+ * is wrapped in a new method handle {@code M},
+ * which is permanently associated with the switch point that created it.
+ * Each pair consists of a target {@code T} and a fallback {@code F}.
+ * While the switch point is valid, invocations to {@code M} are delegated to {@code T}.
+ * After it is invalidated, invocations are delegated to {@code F}.
+ * <p>
+ * Invalidation is global and immediate, as if the switch point contained a
+ * volatile boolean variable consulted on every call to {@code M}.
+ * The invalidation is also permanent, which means the switch point
+ * can change state only once.
+ * The switch point will always delegate to {@code F} after being invalidated.
+ * At that point {@code guardWithTest} may ignore {@code T} and return {@code F}.
+ * <p>
+ * Here is an example of a switch point in action:
+ * <blockquote><pre>
+MethodType MT_str2 = MethodType.methodType(String.class, String.class);
+MethodHandle MH_strcat = MethodHandles.lookup()
+ .findVirtual(String.class, "concat", MT_str2);
+SwitchPoint spt = new SwitchPoint();
+// the following steps may be repeated to re-use the same switch point:
+MethodHandle worker1 = strcat;
+MethodHandle worker2 = MethodHandles.permuteArguments(strcat, MT_str2, 1, 0);
+MethodHandle worker = spt.guardWithTest(worker1, worker2);
+assertEquals("method", (String) worker.invokeExact("met", "hod"));
+SwitchPoint.invalidateAll(new SwitchPoint[]{ spt });
+assertEquals("hodmet", (String) worker.invokeExact("met", "hod"));
+ * </pre></blockquote>
+ * <p style="font-size:smaller;">
+ * <em>Discussion:</em>
+ * Switch points are useful without subclassing. They may also be subclassed.
+ * This may be useful in order to associate application-specific invalidation logic
+ * with the switch point.
+ * Notice that there is no permanent association between a switch point and
+ * the method handles it produces and consumes.
+ * The garbage collector may collect method handles produced or consumed
+ * by a switch point independently of the lifetime of the switch point itself.
+ * <p style="font-size:smaller;">
+ * <em>Implementation Note:</em>
+ * A switch point behaves as if implemented on top of {@link MutableCallSite},
+ * approximately as follows:
+ * <blockquote><pre>
+public class SwitchPoint {
+ private static final MethodHandle
+ K_true = MethodHandles.constant(boolean.class, true),
+ K_false = MethodHandles.constant(boolean.class, false);
+ private final MutableCallSite mcs;
+ private final MethodHandle mcsInvoker;
+ public SwitchPoint() {
+ this.mcs = new MutableCallSite(K_true);
+ this.mcsInvoker = mcs.dynamicInvoker();
+ }
+ public MethodHandle guardWithTest(
+ MethodHandle target, MethodHandle fallback) {
+ // Note: mcsInvoker is of type ()boolean.
+ // Target and fallback may take any arguments, but must have the same type.
+ return MethodHandles.guardWithTest(this.mcsInvoker, target, fallback);
+ }
+ public static void invalidateAll(SwitchPoint[] spts) {
+ List<MutableCallSite> mcss = new ArrayList<>();
+ for (SwitchPoint spt : spts) mcss.add(spt.mcs);
+ for (MutableCallSite mcs : mcss) mcs.setTarget(K_false);
+ MutableCallSite.syncAll(mcss.toArray(new MutableCallSite[0]));
+ }
+}
+ * </pre></blockquote>
+ * @author Remi Forax, JSR 292 EG
+ */
+public class SwitchPoint {
+ private static final MethodHandle
+ K_true = MethodHandles.constant(boolean.class, true),
+ K_false = MethodHandles.constant(boolean.class, false);
+
+ private final MutableCallSite mcs;
+ private final MethodHandle mcsInvoker;
+
+ /**
+ * Creates a new switch point.
+ */
+ public SwitchPoint() {
+ this.mcs = new MutableCallSite(K_true);
+ this.mcsInvoker = mcs.dynamicInvoker();
+ }
+
+ /**
+ * Returns a method handle which always delegates either to the target or the fallback.
+ * The method handle will delegate to the target exactly as long as the switch point is valid.
+ * After that, it will permanently delegate to the fallback.
+ * <p>
+ * The target and fallback must be of exactly the same method type,
+ * and the resulting combined method handle will also be of this type.
+ *
+ * @param target the method handle selected by the switch point as long as it is valid
+ * @param fallback the method handle selected by the switch point after it is invalidated
+ * @return a combined method handle which always calls either the target or fallback
+ * @throws NullPointerException if either argument is null
+ * @see MethodHandles#guardWithTest
+ */
+ public MethodHandle guardWithTest(MethodHandle target, MethodHandle fallback) {
+ if (mcs.getTarget() == K_false)
+ return fallback; // already invalid
+ return MethodHandles.guardWithTest(mcsInvoker, target, fallback);
+ }
+
+ /**
+ * Sets all of the given switch points into the invalid state.
+ * After this call executes, no thread will observe any of the
+ * switch points to be in a valid state.
+ * <p>
+ * This operation is likely to be expensive and should be used sparingly.
+ * If possible, it should be buffered for batch processing on sets of switch points.
+ * <p>
+ * If {@code switchPoints} contains a null element,
+ * a {@code NullPointerException} will be raised.
+ * In this case, some non-null elements in the array may be
+ * processed before the method returns abnormally.
+ * Which elements these are (if any) is implementation-dependent.
+ *
+ * <p style="font-size:smaller;">
+ * <em>Discussion:</em>
+ * For performance reasons, {@code invalidateAll} is not a virtual method
+ * on a single switch point, but rather applies to a set of switch points.
+ * Some implementations may incur a large fixed overhead cost
+ * for processing one or more invalidation operations,
+ * but a small incremental cost for each additional invalidation.
+ * In any case, this operation is likely to be costly, since
+ * other threads may have to be somehow interrupted
+ * in order to make them notice the updated switch point state.
+ * However, it may be observed that a single call to invalidate
+ * several switch points has the same formal effect as many calls,
+ * each on just one of the switch points.
+ *
+ * <p style="font-size:smaller;">
+ * <em>Implementation Note:</em>
+ * Simple implementations of {@code SwitchPoint} may use
+ * a private {@link MutableCallSite} to publish the state of a switch point.
+ * In such an implementation, the {@code invalidateAll} method can
+ * simply change the call site's target, and issue one call to
+ * {@linkplain MutableCallSite#syncAll synchronize} all the
+ * private call sites.
+ *
+ * @param switchPoints an array of call sites to be synchronized
+ * @throws NullPointerException if the {@code switchPoints} array reference is null
+ * or the array contains a null
+ */
+ public static void invalidateAll(SwitchPoint[] switchPoints) {
+ if (switchPoints.length == 0) return;
+ MutableCallSite[] sites = new MutableCallSite[switchPoints.length];
+ for (int i = 0; i < switchPoints.length; i++) {
+ SwitchPoint spt = switchPoints[i];
+ if (spt == null) break; // MSC.syncAll will trigger a NPE
+ sites[i] = spt.mcs;
+ spt.mcs.setTarget(K_false);
+ }
+ MutableCallSite.syncAll(sites);
+ }
+}