/*  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 com.lmax.disruptor.util;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;


import static java.lang.invoke.MethodType.methodType;

This class captures possible hints that may be used by some runtimes to improve code performance. It is intended to capture hinting behaviours that are implemented in or anticipated to be spec'ed under the Thread class in some Java SE versions, but missing in prior versions. /**
 * This class captures possible hints that may be used by some
 * runtimes to improve code performance. It is intended to capture hinting
 * behaviours that are implemented in or anticipated to be spec'ed under the
 * {@link java.lang.Thread} class in some Java SE versions, but missing in prior
 * versions.
 */
public final class ThreadHints
{
    private static final MethodHandle ON_SPIN_WAIT_METHOD_HANDLE;

    static
    {
        final MethodHandles.Lookup lookup = MethodHandles.lookup();

        MethodHandle methodHandle = null;
        try
        {
            methodHandle = lookup.findStatic(Thread.class, "onSpinWait", methodType(void.class));
        }
        catch (final Exception ignore)
        {
        }

        ON_SPIN_WAIT_METHOD_HANDLE = methodHandle;
    }

    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.
/**
     * 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()
    {
        // Call java.lang.Thread.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.Thread.onSpinWait()
        if (null != ON_SPIN_WAIT_METHOD_HANDLE)
        {
            try
            {
                ON_SPIN_WAIT_METHOD_HANDLE.invokeExact();
            }
            catch (final Throwable ignore)
            {
            }
        }
    }
}