/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j 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.
 *
 * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.resources;

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;

/**
 * Measures CPU time by thread.
 */
public interface CpuClock {
    CpuClock CPU_CLOCK = new CpuClock() {
        private final ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();

        @Override
        public long cpuTimeNanos(long threadId) {
            if (!threadMXBean.isThreadCpuTimeSupported()) {
                return -1;
            }
            if (!threadMXBean.isThreadCpuTimeEnabled()) {
                threadMXBean.setThreadCpuTimeEnabled(true);
            }
            return threadMXBean.getThreadCpuTime(threadId);
        }
    };
    CpuClock NOT_AVAILABLE = threadId -> -1;

    /**
     * Returns the current CPU time used by the thread, in nanoseconds.
     *
     * @param threadId
     *         the id of the thread to get the used CPU time for.
     * @return the current CPU time used by the thread, in nanoseconds, or {@code -1} if getting the CPU time is not
     * supported.
     */
    long cpuTimeNanos(long threadId);
}
