RefCnt.java — netty Source File

Source Code

/*
 * Copyright 2025 The Netty Project
 *
 * The Netty Project licenses this file to you 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:
 *
 *   https://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 io.netty.util.internal;

import io.netty.util.IllegalReferenceCountException;

import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;

import static io.netty.util.internal.ObjectUtil.checkPositive;

/**
 * Monomorphic reference counter implementation that always use the most efficient available atomic updater.
 * This implementation is easier for the JIT compiler to optimize,
 * compared to when {@link ReferenceCountUpdater} is used.
 */
@SuppressWarnings("deprecation")
public final class RefCnt {

    private static final int UNSAFE = 0;
    private static final int VAR_HANDLE = 1;
    private static final int ATOMIC_UPDATER = 2;
    private static final int REF_CNT_IMPL;

    static {
        if (PlatformDependent.hasUnsafe()) {
            REF_CNT_IMPL = UNSAFE;
        } else if (PlatformDependent.hasVarHandle()) {
            REF_CNT_IMPL = VAR_HANDLE;
        } else {
            REF_CNT_IMPL = ATOMIC_UPDATER;
        }
    }

    /*
     * Implementation notes:
     *
     * For the updated int field:
     *   Even => "real" refcount is (refCnt >>> 1)
     *   Odd  => "real" refcount is 0
     *
     * This field is package-private so that the AtomicRefCnt implementation can reach it, even on native-image.
     */
    volatile int value;

    public RefCnt() {
// ... (417 more lines)