Fix the GC value is incorrect (#1147)

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

@@ -30,8 +30,10 @@ import org.apache.skywalking.apm.network.proto.GCPhrase;
 public abstract class GCModule implements GCMetricAccessor {
     private List<GarbageCollectorMXBean> beans;
 
-    private long lastGCCount = 0;
-    private long lastCollectionTime = 0;
+    private long lastOGCCount = 0;
+    private long lastYGCCount = 0;
+    private long lastOGCCollectionTime = 0;
+    private long lastYGCCollectionTime = 0;
 
     public GCModule(List<GarbageCollectorMXBean> beans) {
         this.beans = beans;
@@ -43,22 +45,30 @@ public abstract class GCModule implements GCMetricAccessor {
         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;
             }
 
-            long collectionCount = bean.getCollectionCount();
-            long gcCount = collectionCount - lastGCCount;
-            lastGCCount = collectionCount;
-
-            long time = bean.getCollectionTime();
-            long gcTime = time - lastCollectionTime;
-            lastCollectionTime = time;
-
             gcList.add(
                 GC.newBuilder().setPhrase(phrase)
                     .setCount(gcCount)