Add jvm shutdown hook

apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/boot/BootService.java

@@ -13,4 +13,6 @@ public interface BootService {
     void boot() throws Throwable;
 
     void afterBoot() throws Throwable;
+
+    void shutdown() throws Throwable;
 }

apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/boot/ServiceManager.java

@@ -27,6 +27,16 @@ public enum ServiceManager {
         afterBoot();
     }
 
+    public void shutdown() {
+        for (BootService service : bootedServices.values()) {
+            try {
+                service.shutdown();
+            } catch (Throwable e) {
+                logger.error(e, "ServiceManager try to shutdown [{}] fail.", service.getClass().getName());
+            }
+        }
+    }
+
     private Map<Class, BootService> loadAllServices() {
         HashMap<Class, BootService> bootedServices = new HashMap<Class, BootService>();
         Iterator<BootService> serviceIterator = load().iterator();

apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/context/ContextManager.java

@@ -162,6 +162,10 @@ public class ContextManager implements TracingContextListener, BootService, Igno
 
     }
 
+    @Override public void shutdown() throws Throwable {
+
+    }
+
     @Override
     public void afterFinished(TraceSegment traceSegment) {
         CONTEXT.remove();

apm-sniffer/apm-agent/src/main/java/org/skywalking/apm/agent/SkyWalkingAgent.java

@@ -44,6 +44,12 @@ public class SkyWalkingAgent {
 
         ServiceManager.INSTANCE.boot();
 
+        Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
+            @Override public void run() {
+                ServiceManager.INSTANCE.shutdown();
+            }
+        }, "skywalking service shutdown thread"));
+
         new AgentBuilder.Default().type(pluginFinder.buildMatch()).transform(new AgentBuilder.Transformer() {
             @Override
             public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder, TypeDescription typeDescription,