这篇博客会先容如何通过JMX 来获取Java 历程占用的CPU操作率和GC所占用的CPU操作率

在利用JVisualVM的时候,发明它可以查察当前JAVA 历程占用的CPU操作率和GC 所占用的CPU操作率,很奇怪它是如何计较的可能怎么获取的.

本文会按照JVisualVM的源码来描写JVisualVM是如何计较的.

获取源码

GITHUB 地点: https://github.com/visualvm/visualvm.src
百度云:http://pan.baidu.com/s/1boHI4HL

方针数据

运行jvisualvm, 方针是获取图中的CPU Usage 和 GC activity.

HOW TO

将源码导入Intellij后,可以全局搜索GC activity,然后可以查察到:
在Bundle.properties 中:

LBL_Gc_Usage=GC activity

然后查察这个property的利用处所:

com.sun.tools.visualvm.application.views.monitor.ApplicationMonitorView.CpuViewSupport
...

        private static final String CPU = NbBundle.getMessage(ApplicationMonitorView.class, "LBL_Cpu"); // NOI18N
        private static final String CPU_USAGE = NbBundle.getMessage(ApplicationMonitorView.class, "LBL_Cpu_Usage"); // NOI18N
        private static final String GC_USAGE = NbBundle.getMessage(ApplicationMonitorView.class, "LBL_Gc_Usage"); // NOI18N
...
private void initModels(ApplicationMonitorModel model) {
            liveModel = model.isLive();
            processorsCount = model.getProcessorsCount();
            cpuMonitoringSupported = model.isCpuMonitoringSupported();
            gcMonitoringSupported = model.isGcMonitoringSupported();

            SimpleXYChartDescriptor chartDescriptor =
                    //下面的这个后头会讲到
                    SimpleXYChartDescriptor.percent(false, 0.1d, model.getChartCache());

            chartDescriptor.addLineItems(CPU_USAGE, GC_USAGE);
            chartDescriptor.setDetailsItems(new String[] { CPU_USAGE, GC_USAGE });

            chartSupport = ChartFactory.createSimpleXYChart(chartDescriptor);
//这里就应该就是界面显示的注册了.   那么注册后是如何利用的???            model.registerCpuChartSupport(chartSupport);

            chartSupport.setZoomingEnabled(!liveModel);
        }

主要的计较逻辑会合在其refresh要领中:

public void refresh(ApplicationMonitorModel model) {
     //假如监控CPU
            if (cpuMonitoringSupported || gcMonitoringSupported) {
     //获取当前的UPTIME
                long upTime = model.getUpTime() * 1000000;
                //获取上次的UPTIME
                long prevUpTime = model.getPrevUpTime() * 1000000;

                boolean tracksProcessCpuTime = cpuMonitoringSupported &&
                                               model.getPrevProcessCpuTime() != -1;
                                               //获取当前的CPU时间
                long processCpuTime = tracksProcessCpuTime ?
                    model.getProcessCpuTime() / processorsCount : -1;
                    //获取上次的CPU时间
                long prevProcessCpuTime = tracksProcessCpuTime ?
                    model.getPrevProcessCpuTime() / processorsCount : -1;

                boolean tracksProcessGcTime  = gcMonitoringSupported &&
                                               model.getPrevProcessGcTime() != -1;
                                               //获取当前的GC占用时间
                long processGcTime  = tracksProcessGcTime  ?
                    model.getProcessGcTime() * 1000000 / processorsCount : -1;
                    //获取上次的GC占用时间
                long prevProcessGcTime  = tracksProcessGcTime  ?
                    model.getPrevProcessGcTime() * 1000000 / processorsCount : -1;

                if (prevUpTime != -1 && (tracksProcessCpuTime || tracksProcessGcTime)) {

                    long upTimeDiff = upTime - prevUpTime;
                    //别离计较CPU利用率和GC的CPU利用率.
                    long cpuUsage = -1;
                    long gcUsage = -1;
                    String cpuDetail = UNKNOWN;
                    String gcDetail = UNKNOWN;

                    if (tracksProcessCpuTime) {
                        long processTimeDiff = processCpuTime - prevProcessCpuTime;
                        cpuUsage = upTimeDiff > 0 ? Math.min((long)(1000 * (float)processTimeDiff /
                                                             (float)upTimeDiff), 1000) : 0;
                        cpuDetail = cpuUsage == -1 ? UNKNOWN : chartSupport.formatPercent(cpuUsage);
                    }

                    if (tracksProcessGcTime) {
                        long processGcTimeDiff = processGcTime - prevProcessGcTime;
                        gcUsage = upTimeDiff > 0 ? Math.min((long)(1000 * (float)processGcTimeDiff /
                                                            (float)upTimeDiff), 1000) : 0;
                        if (cpuUsage != -1 && cpuUsage < gcUsage) gcUsage = cpuUsage;
                        gcDetail = gcUsage == -1 ? UNKNOWN : chartSupport.formatPercent(gcUsage);
                    }

                    if (liveModel)
                        //配置视图的值 到达刷新的目标
                        //可以看到这个值和界面上显示是相差0.1倍的 原因是前面的谁人chartDescriptor 有个0.1d的显示倍率.
                        chartSupport.addValues(model.getTimestamp(), new long[] { Math.max(cpuUsage, 0), Math.max(gcUsage, 0) });
                    chartSupport.updateDetails(new String[] { cpuDetail, gcDetail });

                }
            }
        }

可以看到逻辑主要是ApplicationMonitorModel model工具的相关要领中,下面先容这些时间是如何获取的:
ApplicationMonitorModel的要领: