聊聊skywalking的GCProvider

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;
        }
    }
}

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();
}