Not able to access InheritableThreadLocal object from parent thread in fall back method

问题

I have InheritableThreadLocal<ConcurrentHashMap<String, Object>> thread that initializes when a request comes via the filter and set some transaction_id in it.

Now at the service layer, I'm calling 10 different API calls via CompletableFuture. All API service class have one execute method that is using RestTempate to make an API call. I put @HystrixCommand on execute method.

execute method is void type but it put the API response in InheritableThreadLocal object.

Problem is when an API call fails Hystrix call FallBackMethod and when I put error response in InheritableThreadLocal, I'm not able to send that error response to the client.

ThreadLocalUtil.class

public class ThreadLocalUtil {

    private static InheritableThreadLocal<ConcurrentHashMap<String, Object>> transmittableThreadLocal = new InheritableThreadLocal<>();

    public static void addDataToThreadLocalMap(String key, Object value) {
        Map<String, Object> existingDataMap = transmittableThreadLocal.get();
        if (value != null) {
            existingDataMap.put(key, value);
        }
    }

    public static Object getDataFromThreadLocalMap(String key) {
        Map<String, Object> existingDataMap = transmittableThreadLocal.get();
        return existingDataMap.get(key);
    }

    public static void clearThreadLocalDataMap() {
        if (transmittableThreadLocal != null) 
            transmittableThreadLocal.remove();
    }

    public static Object getRequestData(String key) {
        Map<String, Object> existingDataMap = transmittableThreadLocal.get();
        if (existingDataMap != null) {
            return existingDataMap.get(key);
        }
        return "-1";
    }

    public static void initThreadLocals() {
        ConcurrentHashMap<String, Object> dataForDataMap = new ConcurrentHashMap<String, Object>();
        String requestId = "REQUEST_ID_" + System.currentTimeMillis();
        dataForDataMap.put("REQUEST_ID", requestId);
        transmittableThreadLocal.set(dataForDataMap);
    }
}

CommonFilter.class

@Component
@Order(1)
public class CommonFilter extends OncePerRequestFilter {

  @Override
  protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
          throws ServletException, IOException {
      try {
          ThreadLocalUtil.initThreadLocals();
          filterChain.doFilter(request, response);
      } catch (Exception e) {
          if (e instanceof ServletException) {
              throw (ServletException) e;
          }
      } finally {
          ThreadLocalUtil.clearThreadLocalDataMap();
      }

  }

EmployeeService.class

@Component
public abstract class EmployeeService {

    @Autowired
    private ThreadLocalUtil threadLocalUtil;

    public abstract void getEmployee(int employeeId);

    public void fallbackMethod(int employeeid) {
        threadLocalUtil.addDataToThreadLocalMap("ErrorResponse", "Fallback response:: No employee details available temporarily");
    }
}

EmployeeServiceImpl.class

@Service
public class EmployeeServiceImpl extends EmployeeService {

    @HystrixCommand(fallbackMethod = "fallbackMethod", commandProperties = {
            @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "900"),
            @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage", value = "10") })
    public void getEmployee(int employeeId) {
        System.out.println("Getting Employee details for " + employeeId + ", threadLocalUtil : " + threadLocalUtil.getDataFromThreadLocalMap("EMPLOYE_ID"));
        String response = restTemplate.exchange("http://localhost:8011/findEmployeeDetails/{employeeid}",
                HttpMethod.GET, null, new ParameterizedTypeReference<String>() {
                }, employeeId).getBody();

        threadLocalUtil.addDataToThreadLocalMap("Response", response);
    }

    @Autowired
    RestTemplate restTemplate;

    @Autowired
    private ThreadLocalUtil threadLocalUtil;
}

回答1:

So, first of all since internally Hystrix uses ThreadPoolExecutor (Threads created once and reused), so it is wrong to use InheritableThreadLocal.

From the above question and what you asked in my blog, I understand that you problem is

InheritableThreadLocal becomes null in hystrix fallback method

Further adding to this (you may verify this)

InheritableThreadLocal becomes null in hystrix fallback method only in case of timeouts and not in case of any other exception

I would recommend others to refer to my blog. Hystrix fallback in case of timeout, takes place in hystrix-timer thread. Hystrix fallback execution thread You can verify this by logging Thread.currentThread().getName()

Since the parent of hystrix-timer thread is not your calling thread, and so your transmittableThreadLocal.get() becomes null.

To solve this I would recommend using HystrixCommandExecutionHook and HystrixRequestVariableDefault. Using this you can implement hooks like onStart, onExecutionStart, onFallbackStart etc., in which you need to get/set the threadLocal variables. For more details you can refer to the last section in the blog.

Update: For your use-case you can modify your code as follows:

ThreadLocalUtil.java

public class ThreadLocalUtil {

    private static ThreadLocal<ConcurrentHashMap<String, Object>> transmittableThreadLocal = new ThreadLocal<>();

    public static ConcurrentHashMap<String, Object> getThreadLocalData() {
        return transmittableThreadLocal.get();
    }

    public static void setThreadLocalData(ConcurrentHashMap<String, Object> data) {
        transmittableThreadLocal.set(data);
    }

    public static void addDataToThreadLocalMap(String key, Object value) {
        Map<String, Object> existingDataMap = transmittableThreadLocal.get();
        if (value != null) {
            existingDataMap.put(key, value);
        }
    }

    public static Object getDataFromThreadLocalMap(String key) {
        Map<String, Object> existingDataMap = transmittableThreadLocal.get();
        return existingDataMap.get(key);
    }

    public static void clearThreadLocalDataMap() {
        if (transmittableThreadLocal != null) 
            transmittableThreadLocal.remove();
    }

    public static Object getRequestData(String key) {
        Map<String, Object> existingDataMap = transmittableThreadLocal.get();
        if (existingDataMap != null) {
            return existingDataMap.get(key);
        }
        return "-1";
    }



    public static void initThreadLocals() {
        transmittableThreadLocal.set(new ConcurrentHashMap<>());
        String requestId = "REQUEST_ID_" + System.currentTimeMillis();
        addDataToThreadLocalMap("REQUEST_ID", requestId);
    }
}

EmployeeService.java

@Component
public abstract class EmployeeService {
    public abstract void getEmployee(int employeeId);

    public void fallbackMethod(int employeeid) {
        threadLocalUtil.addDataToThreadLocalMap("ErrorResponse", "Fallback response:: No employee details available temporarily");
    }
}

EmployeeServiceImpl.java

@Service
public class EmployeeServiceImpl extends EmployeeService {

    @HystrixCommand(fallbackMethod = "fallbackMethod", commandProperties = {
            @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "900"),
            @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage", value = "10") })
    public void getEmployee(int employeeId) {
        System.out.println("Getting Employee details for " + employeeId + ", threadLocalUtil : " + threadLocalUtil.getDataFromThreadLocalMap("EMPLOYEE_ID"));
        String response = restTemplate.exchange("http://localhost:8011/findEmployeeDetails/{employeeid}",
                HttpMethod.GET, null, new ParameterizedTypeReference<String>() {
                }, employeeId).getBody();

        threadLocalUtil.addDataToThreadLocalMap("Response", response);
    }

    @Autowired
    RestTemplate restTemplate;
}

HystrixHook.java

public class HystrixHook extends HystrixCommandExecutionHook {

    private HystrixRequestVariableDefault<ConcurrentHashMap<String, Object>> hrv = new HystrixRequestVariableDefault<>();

    @Override
    public <T> void onStart(HystrixInvokable<T> commandInstance) {
        HystrixRequestContext.initializeContext();
        getThreadLocals();
    }

    @Override
    public <T> void onExecutionStart(HystrixInvokable<T> commandInstance) {
        setThreadLocals();
    }


    @Override
    public <T> void onFallbackStart(HystrixInvokable<T> commandInstance) {
        setThreadLocals();
    }


    @Override
    public <T> void onSuccess(HystrixInvokable<T> commandInstance) {
        HystrixRequestContext.getContextForCurrentThread().shutdown();
        super.onSuccess(commandInstance);
    }

    @Override
    public <T> Exception onError(HystrixInvokable<T> commandInstance, HystrixRuntimeException.FailureType failureType, Exception e) {
        HystrixRequestContext.getContextForCurrentThread().shutdown();
        return super.onError(commandInstance, failureType, e);
    }

    private void getThreadLocals() {
        hrv.set(ThreadLocalUtil.getThreadLocalData());
    }

    private void setThreadLocals() {
        ThreadLocalUtil.setThreadLocalData(hrv.get());
    }
}

AbcApplication.java

public class AbcApplication {
    public static void main(String[] args) {
        HystrixPlugins.getInstance().registerCommandExecutionHook(new HystrixHook());
        SpringApplication.run(Abc.class, args);
    }
}

Hope this helps

来源：https://stackoverflow.com/questions/55862601/not-able-to-access-inheritablethreadlocal-object-from-parent-thread-in-fall-back