Getting cpu usage in java instance, that limits in executing java virtual machine, not os.


Have a look at the java class sun.tools.jconsole.SummaryTab.java in open JDK7 or source in web.(http://www.docjar.com/html/api/sun/tools/jconsole/SummaryTab$Result.java.html)

If you know JConsole, you know that cpu usages graph. that source is below.

  354       private static class CPUOverviewPanel extends OverviewPanel {
  355           private long prevUpTime, prevProcessCpuTime;
  356   
  357           CPUOverviewPanel() {
  358               super(getText("CPU Usage"), cpuUsageKey, cpuUsageName, Plotter.Unit.PERCENT);
  359               getPlotter().setDecimals(CPU_DECIMALS);
  360           }
  361   
  362           public void updateCPUInfo(Result result) {
  363               if (prevUpTime > 0L && result.upTime > prevUpTime) {
  364                   // elapsedCpu is in ns and elapsedTime is in ms.
  365                   long elapsedCpu = result.processCpuTime - prevProcessCpuTime;
  366                   long elapsedTime = result.upTime - prevUpTime;
  367                   // cpuUsage could go higher than 100% because elapsedTime
  368                   // and elapsedCpu are not fetched simultaneously. Limit to
  369                   // 99% to avoid Plotter showing a scale from 0% to 200%.
  370                   float cpuUsage =
  371                       Math.min(99F,
  372                                elapsedCpu / (elapsedTime * 10000F * result.nCPUs));
  373   
  374                   getPlotter().addValues(result.timeStamp,
  375                                   Math.round(cpuUsage * Math.pow(10.0, CPU_DECIMALS)));
  376                   getInfoLabel().setText(getText(cpuUsageFormat,
  377                                                  String.format("%."+CPU_DECIMALS+"f", cpuUsage)));
  378               }
  379               this.prevUpTime = result.upTime;
  380               this.prevProcessCpuTime = result.processCpuTime;
  381           }
  382       }



So. I made my own class to get java-cpu usage.
private void _getJavaRuntime() {
OperatingSystemMXBean osbean = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
RuntimeMXBean runbean = (RuntimeMXBean) ManagementFactory.getRuntimeMXBean();
int nCPUs = osbean.getAvailableProcessors();
long prevUpTime = runbean.getUptime();
long prevProcessCpuTime = osbean.getProcessCpuTime();
try {
Thread.sleep(500);
} catch (Exception e) { }
osbean = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
long upTime = runbean.getUptime();
long processCpuTime = osbean.getProcessCpuTime();
if (prevUpTime > 0L && upTime > prevUpTime) {
long elapsedCpu = processCpuTime - prevProcessCpuTime;
long elapsedTime = upTime - prevUpTime;
javacpu = Math.min(99F, elapsedCpu / (elapsedTime * 10000F * nCPUs));
} else {
javacpu = 0.001;
}
uptime = runbean.getUptime(); 
}


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