/*
 * Copyright 2017 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:
 *
 *   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 io.netty.util;

import io.netty.util.internal.ObjectUtil;
import io.netty.util.internal.SystemPropertyUtil;

import java.util.Locale;

A utility class for wrapping calls to Runtime. /**
 * A utility class for wrapping calls to {@link Runtime}.
 */
public final class NettyRuntime {

    
Holder class for available processors to enable testing.
/**
     * Holder class for available processors to enable testing.
     */
    static class AvailableProcessorsHolder {

        private int availableProcessors;

        
Set the number of available processors.
Params:
availableProcessors – the number of available processors
Throws:
IllegalArgumentException – if the specified number of available processors is non-positive
IllegalStateException –    if the number of available processors is already configured/**
         * Set the number of available processors.
         *
         * @param availableProcessors the number of available processors
         * @throws IllegalArgumentException if the specified number of available processors is non-positive
         * @throws IllegalStateException    if the number of available processors is already configured
         */
        synchronized void setAvailableProcessors(final int availableProcessors) {
            ObjectUtil.checkPositive(availableProcessors, "availableProcessors");
            if (this.availableProcessors != 0) {
                final String message = String.format(
                        Locale.ROOT,
                        "availableProcessors is already set to [%d], rejecting [%d]",
                        this.availableProcessors,
                        availableProcessors);
                throw new IllegalStateException(message);
            }
            this.availableProcessors = availableProcessors;
        }

        
Get the configured number of available processors. The default is Runtime.availableProcessors(). This can be overridden by setting the system property "io.netty.availableProcessors" or by invoking setAvailableProcessors(int) before any calls to this method. 
Returns:
the configured number of available processors/**
         * Get the configured number of available processors. The default is {@link Runtime#availableProcessors()}.
         * This can be overridden by setting the system property "io.netty.availableProcessors" or by invoking
         * {@link #setAvailableProcessors(int)} before any calls to this method.
         *
         * @return the configured number of available processors
         */
        @SuppressForbidden(reason = "to obtain default number of available processors")
        synchronized int availableProcessors() {
            if (this.availableProcessors == 0) {
                final int availableProcessors =
                        SystemPropertyUtil.getInt(
                                "io.netty.availableProcessors",
                                Runtime.getRuntime().availableProcessors());
                setAvailableProcessors(availableProcessors);
            }
            return this.availableProcessors;
        }
    }

    private static final AvailableProcessorsHolder holder = new AvailableProcessorsHolder();

    
Set the number of available processors.
Params:
availableProcessors – the number of available processors
Throws:
IllegalArgumentException – if the specified number of available processors is non-positive
IllegalStateException –    if the number of available processors is already configured/**
     * Set the number of available processors.
     *
     * @param availableProcessors the number of available processors
     * @throws IllegalArgumentException if the specified number of available processors is non-positive
     * @throws IllegalStateException    if the number of available processors is already configured
     */
    @SuppressWarnings("unused,WeakerAccess") // this method is part of the public API
    public static void setAvailableProcessors(final int availableProcessors) {
        holder.setAvailableProcessors(availableProcessors);
    }

    
Get the configured number of available processors. The default is Runtime.availableProcessors(). This can be overridden by setting the system property "io.netty.availableProcessors" or by invoking setAvailableProcessors(int) before any calls to this method. 
Returns:
the configured number of available processors/**
     * Get the configured number of available processors. The default is {@link Runtime#availableProcessors()}. This
     * can be overridden by setting the system property "io.netty.availableProcessors" or by invoking
     * {@link #setAvailableProcessors(int)} before any calls to this method.
     *
     * @return the configured number of available processors
     */
    public static int availableProcessors() {
        return holder.availableProcessors();
    }

    
No public constructor to prevent instances from being created.
/**
     * No public constructor to prevent instances from being created.
     */
    private NettyRuntime() {
    }
}