com.google.apphosting.runtime.timer.JmxCpuTimer Maven / Gradle / Ivy
/*
* Copyright 2021 Google LLC
*
* 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
*
* 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 com.google.apphosting.runtime.timer;
import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;
/**
* Use the JMX {@link ThreadMXBean} to retrieve CPU timing information
* about a particular {@link Thread}.
*
* Counts the number of nanoseconds that this thread spent on a CPU.
* The JVM implements this with a fast path and a slow path. The fast
* path involves calling {@code pthread_getcpuclockid} and passing the
* resulting clock to {@code clock_gettime}, and is only used if
* {@code -XX:+UseLinuxPosixThreadCPUClocks} is set and if
* {@code clock_getres} on an arbitrary CPU clock returns < 1 second.
* The slow path involves reading from
* {@code /proc/self/task//stat}.
*
*/
class JmxCpuTimer extends AbstractIntervalTimer {
private static final ThreadMXBean THREAD_MX = ManagementFactory.getThreadMXBean();
private final long threadId;
/**
* Creates a new {@code JmxCpuTimer} initialized with the specified
* {@code Thread}. As a side-effect, also ensures that CPU thread
* timing is enabled.
*/
public JmxCpuTimer(Thread thread) {
this.threadId = thread.getId();
THREAD_MX.setThreadCpuTimeEnabled(true);
}
/**
* Returns true if the current JVM supports thread cpu timing via
* {@code ThreadMXBean}.
*/
public static boolean isAvailable() {
return THREAD_MX.isThreadCpuTimeSupported();
}
@Override
protected long getCurrent() {
// This returns the combined user and system time.
return THREAD_MX.getThreadCpuTime(threadId);
}
}