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CloudSim Plus: A modern, highly extensible and easier-to-use Java 8 Framework for Modeling and Simulation of Cloud Computing Infrastructures and Services

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/*
 * CloudSim Plus: A modern, highly-extensible and easier-to-use Framework for
 * Modeling and Simulation of Cloud Computing Infrastructures and Services.
 * http://cloudsimplus.org
 *
 *     Copyright (C) 2015-2021 Universidade da Beira Interior (UBI, Portugal) and
 *     the Instituto Federal de Educação Ciência e Tecnologia do Tocantins (IFTO, Brazil).
 *
 *     This file is part of CloudSim Plus.
 *
 *     CloudSim Plus is free software: you can redistribute it and/or modify
 *     it under the terms of the GNU General Public License as published by
 *     the Free Software Foundation, either version 3 of the License, or
 *     (at your option) any later version.
 *
 *     CloudSim Plus 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 for more details.
 *
 *     You should have received a copy of the GNU General Public License
 *     along with CloudSim Plus. If not, see .
 */
package org.cloudbus.cloudsim.allocationpolicies;

import org.cloudbus.cloudsim.distributions.ContinuousDistribution;
import org.cloudbus.cloudsim.hosts.Host;
import org.cloudbus.cloudsim.vms.Vm;

import java.util.Objects;
import java.util.Optional;

/**
 * A VM allocation policy
 * which finds a random Host having suitable resources to place a given VM.
 * This is a high time-efficient policy with a best-case complexity O(1)
 * and a worst-case complexity O(N), where N is the number of Hosts.
 *
 * 
 *     NOTES:
 *     

 *         This policy doesn't perform optimization of VM allocation by means of VM migration.
 *         It has a low computational complexity (high time-efficient) but may return
 *         and inactive Host that will be activated, while there may be active Hosts
 *         suitable for the VM.
 *         Despite the low computational complexity, such a policy may increase the number of active Hosts,
 *         that increases power consumption.
 *     
 * 
 *
 * @author Manoel Campos da Silva Filho
 * @since CloudSim Plus 4.4.2
 */
public class VmAllocationPolicyRandom extends VmAllocationPolicyAbstract implements VmAllocationPolicy {
    /**
     * A Pseudo-Random Number Generator (PRNG) used to select a Host.
     */
    private final ContinuousDistribution random;

    /**
     * Instantiates a VmAllocationPolicyRandom.
     *
     * @param random a Pseudo-Random Number Generator (PRNG) used to select a Host.
     *               The PRNG must return values between 0 and 1.
     */
    public VmAllocationPolicyRandom(final ContinuousDistribution random){
        super();
        this.random = Objects.requireNonNull(random);
    }

    @Override
    protected Optional defaultFindHostForVm(final Vm vm) {
        final var hostList = getHostList();
        /* The for loop just defines the maximum number of Hosts to try.
         * When a suitable Host is found, the method returns immediately. */
        final int maxTries = hostList.size();
        for (int i = 0; i < maxTries; i++) {
            final int hostIndex = (int)(random.sample() * hostList.size());
            final var host = hostList.get(hostIndex);
            if (host.isSuitableForVm(vm)) {
                return Optional.of(host);
            }
        }

        return Optional.empty();
    }
}