聊聊skywalking的GCProvider

序

本文主要研究一下skywalking的GCProvider

GCProvider

skywalking-6.6.0/apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/jvm/gc/GCProvider.java

public enum GCProvider {
    INSTANCE;

    private GCMetricAccessor metricAccessor;
    private List<GarbageCollectorMXBean> beans;

    GCProvider() {
        beans = ManagementFactory.getGarbageCollectorMXBeans();
        for (GarbageCollectorMXBean bean : beans) {
            String name = bean.getName();
            GCMetricAccessor accessor = findByBeanName(name);
            if (accessor != null) {
                metricAccessor = accessor;
                break;
            }
        }

        if (metricAccessor == null) {
            this.metricAccessor = new UnknowGC();
        }
    }

    public List<GC> getGCList() {
        return metricAccessor.getGCList();
    }

    private GCMetricAccessor findByBeanName(String name) {
        if (name.indexOf("PS") > -1) {
            //Parallel (Old) collector ( -XX:+UseParallelOldGC )
            return new ParallelGCModule(beans);
        } else if (name.indexOf("ConcurrentMarkSweep") > -1) {
            // CMS collector ( -XX:+UseConcMarkSweepGC )
            return new CMSGCModule(beans);
        } else if (name.indexOf("G1") > -1) {
            // G1 collector ( -XX:+UseG1GC )
            return new G1GCModule(beans);
        } else if (name.equals("MarkSweepCompact")) {
            // Serial collector ( -XX:+UseSerialGC )
            return new SerialGCModule(beans);
        } else {
            // Unknown
            return null;
        }
    }
}

• GCProvider的构造器通过ManagementFactory.getGarbageCollectorMXBeans()获取GarbageCollectorMXBean列表，之后遍历该列表获取GCMetricAccessor，如果找不到则默认为UnknowGC(返回空的的NEW、OLD指标)；其getGCList则通过metricAccessor.getGCList()返回GC指标

GCModule

skywalking-6.6.0/apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/jvm/gc/GCModule.java

public abstract class GCModule implements GCMetricAccessor {
    private List<GarbageCollectorMXBean> beans;

    private long lastOGCCount = 0;
    private long lastYGCCount = 0;
    private long lastOGCCollectionTime = 0;
    private long lastYGCCollectionTime = 0;

    public GCModule(List<GarbageCollectorMXBean> beans) {
        this.beans = beans;
    }

    @Override
    public List<GC> getGCList() {
        List<GC> gcList = new LinkedList<GC>();
        for (GarbageCollectorMXBean bean : beans) {
            String name = bean.getName();
            GCPhrase phrase;
            long gcCount = 0;
            long gcTime = 0;
            if (name.equals(getNewGCName())) {
                phrase = GCPhrase.NEW;
                long collectionCount = bean.getCollectionCount();
                gcCount = collectionCount - lastYGCCount;
                lastYGCCount = collectionCount;

                long time = bean.getCollectionTime();
                gcTime = time - lastYGCCollectionTime;
                lastYGCCollectionTime = time;
            } else if (name.equals(getOldGCName())) {
                phrase = GCPhrase.OLD;
                long collectionCount = bean.getCollectionCount();
                gcCount = collectionCount - lastOGCCount;
                lastOGCCount = collectionCount;

                long time = bean.getCollectionTime();
                gcTime = time - lastOGCCollectionTime;
                lastOGCCollectionTime = time;
            } else {
                continue;
            }

            gcList.add(
                GC.newBuilder().setPhrase(phrase)
                    .setCount(gcCount)
                    .setTime(gcTime)
                    .build()
            );
        }

        return gcList;
    }

    protected abstract String getOldGCName();

    protected abstract String getNewGCName();
}

• GCModule声明实现了GCMetricAccessor接口，其getGCList方法通过遍历GarbageCollectorMXBean列表计算gcCount、gcTime，并维护lastYGCCount、lastYGCCollectionTime、lastOGCCount、lastOGCCollectionTime指标；由于不同垃圾收集器的NEW、OLD名称不一样，因而这里通过抽象方法暴露给子类去实现，其子类有SerialGCModule、ParallelGCModule、CMSGCModule、G1GCModule

小结

GCProvider的构造器通过ManagementFactory.getGarbageCollectorMXBeans()获取GarbageCollectorMXBean列表，之后遍历该列表获取GCMetricAccessor，如果找不到则默认为UnknowGC(返回空的的NEW、OLD指标)；其getGCList则通过metricAccessor.getGCList()返回GC指标

doc

• GCProvider