Merge branch 'feature/alarm' of...

Merge branch 'feature/alarm' of https://github.com/peng-yongsheng/incubator-skywalking into feature/alarm

apm-commons/apm-util/src/main/java/org/apache/skywalking/apm/util/StringUtil.java

@@ -21,10 +21,7 @@ package org.apache.skywalking.apm.util;
 
 public final class StringUtil {
     public static boolean isEmpty(String str) {
-        if (str == null || "".equals(str) || str.length() == 0) {
-            return true;
-        }
-        return false;
+        return str == null || str.length() == 0;
     }
 
     public static String join(final char delimiter, final String... strings) {

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

@@ -35,6 +35,8 @@ import org.apache.skywalking.apm.agent.core.context.trace.WithPeerInfo;
 import org.apache.skywalking.apm.agent.core.dictionary.DictionaryManager;
 import org.apache.skywalking.apm.agent.core.dictionary.DictionaryUtil;
 import org.apache.skywalking.apm.agent.core.dictionary.PossibleFound;
+import org.apache.skywalking.apm.agent.core.logging.api.ILog;
+import org.apache.skywalking.apm.agent.core.logging.api.LogManager;
 import org.apache.skywalking.apm.agent.core.sampling.SamplingService;
 
 /**
@@ -52,6 +54,9 @@ import org.apache.skywalking.apm.agent.core.sampling.SamplingService;
  * @author zhang xin
  */
 public class TracingContext implements AbstractTracerContext {
+    private static final ILog logger = LogManager.getLogger(TracingContext.class);
+    private long lastWarningTimestamp = 0;
+
     /**
      * @see {@link SamplingService}
      */
@@ -506,6 +511,16 @@ public class TracingContext implements AbstractTracerContext {
     }
 
     private boolean isLimitMechanismWorking() {
-        return spanIdGenerator >= Config.Agent.SPAN_LIMIT_PER_SEGMENT;
+        if (spanIdGenerator >= Config.Agent.SPAN_LIMIT_PER_SEGMENT) {
+            long currentTimeMillis = System.currentTimeMillis();
+            if (currentTimeMillis - lastWarningTimestamp > 30 * 1000) {
+                logger.warn(new RuntimeException("Shadow tracing context. Thread dump"), "More than {} spans required to create",
+                    Config.Agent.SPAN_LIMIT_PER_SEGMENT);
+                lastWarningTimestamp = currentTimeMillis;
+            }
+            return true;
+        } else {
+            return false;
+        }
     }
 }