Enhance hystrix plugin,see https://github.com/apache/skywalking/issues/4850 (#4857)

apm-sniffer/apm-sdk-plugin/hystrix-1.x-plugin/src/main/java/org/apache/skywalking/apm/plugin/hystrix/v1/SWHystrixConcurrencyStrategyWrapper.java

@@ -21,6 +21,9 @@ package org.apache.skywalking.apm.plugin.hystrix.v1;
 
 import com.netflix.hystrix.strategy.concurrency.HystrixConcurrencyStrategy;
 import java.util.concurrent.Callable;
+
+import com.netflix.hystrix.strategy.concurrency.HystrixRequestVariable;
+import com.netflix.hystrix.strategy.concurrency.HystrixRequestVariableLifecycle;
 import org.apache.skywalking.apm.agent.core.conf.RuntimeContextConfiguration;
 import org.apache.skywalking.apm.agent.core.context.ContextManager;
 import org.apache.skywalking.apm.agent.core.context.RuntimeContextSnapshot;
@@ -39,6 +42,11 @@ public class SWHystrixConcurrencyStrategyWrapper extends HystrixConcurrencyStrat
         return new WrappedCallable<T>(ContextManager.getRuntimeContext().capture(), delegateCallable);
     }
 
+    @Override
+    public <T> HystrixRequestVariable<T> getRequestVariable(HystrixRequestVariableLifecycle<T> rv) {
+        return new SWHystrixLifecycleForwardingRequestVariable(rv);
+    }
+
     static class WrappedCallable<T> implements Callable<T> {
 
         private final RuntimeContextSnapshot contextSnapshot;

apm-sniffer/apm-sdk-plugin/hystrix-1.x-plugin/src/main/java/org/apache/skywalking/apm/plugin/hystrix/v1/SWHystrixLifecycleForwardingRequestVariable.java

@@ -0,0 +1,84 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ *
+ */
+
+package org.apache.skywalking.apm.plugin.hystrix.v1;
+
+import com.netflix.hystrix.strategy.concurrency.HystrixRequestContext;
+import com.netflix.hystrix.strategy.concurrency.HystrixRequestVariable;
+import com.netflix.hystrix.strategy.concurrency.HystrixRequestVariableDefault;
+import com.netflix.hystrix.strategy.concurrency.HystrixRequestVariableLifecycle;
+import com.netflix.hystrix.strategy.concurrency.HystrixConcurrencyStrategy;
+
+/**
+ * Implementation of {@link HystrixRequestVariable} which forwards to the wrapped
+ * {@link HystrixRequestVariableLifecycle}.
+ * <p>
+ * This implementation also returns null when {@link #get()} is called while the {@link HystrixRequestContext} has not
+ * been initialized rather than throwing an exception, allowing for use in a {@link HystrixConcurrencyStrategy} which
+ * does not depend on an a HystrixRequestContext
+ */
+public class SWHystrixLifecycleForwardingRequestVariable<T> extends HystrixRequestVariableDefault<T> {
+    private final HystrixRequestVariableLifecycle<T> lifecycle;
+
+    /**
+     * Creates a HystrixRequestVariable which will return data as provided by the {@link HystrixRequestVariableLifecycle}
+     *
+     * @param lifecycle lifecycle used to provide values. Must have the same type parameter as the constructed instance.
+     */
+    public SWHystrixLifecycleForwardingRequestVariable(HystrixRequestVariableLifecycle<T> lifecycle) {
+        this.lifecycle = lifecycle;
+    }
+
+    /**
+     * Delegates to the wrapped {@link HystrixRequestVariableLifecycle}
+     *
+     * @return T with initial value or null if none.
+     */
+    @Override
+    public T initialValue() {
+        return lifecycle.initialValue();
+    }
+
+    /**
+     * Delegates to the wrapped {@link HystrixRequestVariableLifecycle}
+     *
+     * @param value of request variable to allow cleanup activity.
+     *              <p>
+     *              If nothing needs to be cleaned up then nothing needs to be done in this method.
+     */
+    @Override
+    public void shutdown(T value) {
+        lifecycle.shutdown(value);
+    }
+
+    /**
+     * Return null if the {@link HystrixRequestContext} has not been initialized for the current thread.
+     * <p>
+     * If {@link HystrixRequestContext} has been initialized then call method in superclass:
+     * {@link HystrixRequestVariableDefault#get()}
+     */
+    @Override
+    public T get() {
+        if (!HystrixRequestContext.isCurrentThreadInitialized()) {
+            return null;
+        }
+        return super.get();
+    }
+
+}