[GitHub] otyyyywangwenbin opened a new issue #1707: ContextManager.continued NPE

[GitBox <gi...@apache.org>]

otyyyywangwenbin opened a new issue #1707: ContextManager.continued NPE
URL: https://github.com/apache/incubator-skywalking/issues/1707
 
 
   I'm try writing a netty plugin and have a cross threads problem
   
   I read doc
   
   1. https://github.com/apache/incubator-skywalking/blob/5.x/docs/cn/Plugin-Development-Guide-CN.md#%E4%B8%89-contextsnapshot
   2. https://github.com/apache/incubator-skywalking/blob/5.x/docs/en/Plugin-Development-Guide.md#contextsnapshot
   
   Capture a ContextSnapshot in another thread and continued ContextSnapshot in below codes:
   ```java
       public void beforeMethod(EnhancedInstance objInst, Method method, Object[] allArguments, Class<?>[] argumentsTypes, MethodInterceptResult result) throws Throwable {
           ChannelHandlerContext context = (ChannelHandlerContext) allArguments[0];
           Object msg = allArguments[1];
           if (msg instanceof HttpRequest) { // Client Request
               System.out.println(">> " + Thread.currentThread().getId() + ":" + context.channel().hashCode());
               Attribute<ContextSnapshot> attr = context.channel().attr(KEY_CONTEXT_SNAPSHOT);
               ContextSnapshot contextSnapshot = attr.get();
               attr.set(null);
               if (contextSnapshot == null) {
                   return;
               }
               ContextManager.continued(contextSnapshot);  (Line: 45)
               HttpRequest request = (HttpRequest) msg;
               ContextCarrier contextCarrier = new ContextCarrier();
               String uri = request.uri();
               AbstractSpan span = ContextManager.createExitSpan(uri, contextCarrier, String.valueOf(context.channel().remoteAddress()));
               Tags.URL.set(span, request.uri());
               Tags.HTTP.METHOD.set(span, request.method().name());
               span.setComponent(COMPONENT_NETTY_HTTP_CLIENT);
               SpanLayer.asHttp(span);
               CarrierItem next = contextCarrier.items();
               while (next.hasNext()) {
                   next = next.next();
                   request.headers().set(next.getHeadKey(), next.getHeadValue());
               }
               context.channel().attr(KEY_CONTEXT_SNAPSHOT).set(ContextManager.capture());
   
               System.out.println("===> encode client request $$$$$$$$ " + Thread.currentThread().getId() + ":" + context.channel().hashCode());
           }
           return;
       }
   ```
   
   skywalking-api.log ：
   ```
   ERROR 2018-09-26 17:29:56:913 InstMethodsInter :  class[class io.netty.handler.codec.http.HttpClientCodec$Encoder] before method[encode] intercept failure
   java.lang.NullPointerException
   	at org.apache.skywalking.apm.agent.core.context.ContextManager.capture(ContextManager.java:143)
   	at org.apache.skywalking.apm.agent.core.context.ContextSnapshot.isFromCurrent(ContextSnapshot.java:119)
   	at org.apache.skywalking.apm.agent.core.context.ContextManager.continued(ContextManager.java:150)
   	at org.apache.skywalking.apm.plugin.netty.EncodeInterceptor.beforeMethod(EncodeInterceptor.java:45)
   	at org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstMethodsInter.intercept(InstMethodsInter.java:82)
   ```
   
   how to resolve this situation？
   skywalking 5.0.0-rc2

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