Fixes JCTools#284 Add support for Thread.onSpinWait() while spinning

jctools-core/src/main/java/org/jctools/util/InternalThreadHints.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2016 Gil Tene
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jctools.util;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+
+final class InternalThreadHints
+{
+
+    private static final MethodHandle onSpinWaitMH;
+
+    static
+    {
+        MethodHandle mh;
+        MethodHandles.Lookup lookup = MethodHandles.lookup();
+        try
+        {
+            mh = lookup.findStatic(java.lang.Thread.class, "onSpinWait", MethodType.methodType(void.class));
+        }
+        catch (Exception e)
+        {
+            mh = null;
+        }
+        onSpinWaitMH = mh;
+    }
+
+    // prevent construction...
+    private InternalThreadHints()
+    {
+    }
+
+    public static void onSpinWait()
+    {
+        // Call java.lang.Runtime.onSpinWait() on Java SE versions that support it. Do nothing otherwise.
+        // This should optimize away to either nothing or to an inlining of java.lang.Runtime.onSpinWait()
+        if (onSpinWaitMH != null)
+        {
+            try
+            {
+                onSpinWaitMH.invokeExact();
+            }
+            catch (Throwable throwable)
+            {
+                // Nothing to do here...
+            }
+        }
+    }
+}

jctools-core/src/main/java/org/jctools/util/ThreadHints.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2016 Gil Tene
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jctools.util;
+
+@InternalAPI
+public final class ThreadHints
+{
+
+    /**
+     * Set this system property to true to disable {@link #onSpinWait()}.
+     */
+    public static final String DISABLE_ON_SPIN_WAIT = "jctools.disable.onSpinWait";
+    private static final boolean okToInvokeInternalThreadHintsCaller;
+
+    static
+    {
+        boolean okToInvokeMHCaller = false;
+        if (!Boolean.getBoolean(DISABLE_ON_SPIN_WAIT))
+        {
+            try
+            {
+                Class.forName("java.lang.invoke.MethodHandle");
+                okToInvokeMHCaller = true;
+            }
+            catch (Exception e)
+            {
+                okToInvokeMHCaller = false;
+            }
+        }
+        // okToInvokeThreadHintsMHCaller will be false for e.g. Java SE 6 and earlier:
+        okToInvokeInternalThreadHintsCaller = okToInvokeMHCaller;
+    }
+
+    // prevent construction...
+    private ThreadHints()
+    {
+    }
+
+    /**
+     * Indicates that the caller is momentarily unable to progress, until the
+     * occurrence of one or more actions on the part of other activities.  By
+     * invoking this method within each iteration of a spin-wait loop construct,
+     * the calling thread indicates to the runtime that it is busy-waiting. The runtime
+     * may take action to improve the performance of invoking spin-wait loop
+     * constructions.
+     */
+    public static void onSpinWait()
+    {
+        if (okToInvokeInternalThreadHintsCaller)
+        {
+            InternalThreadHints.onSpinWait();
+        }
+    }
+}