GitHub user vio-lin edited a discussion: [Q/A][Java SDK (Component)] Should
RpcInvocation attribute reused in MergeableCluster
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- [X] I am sure that all the content I provide is in English.
### Apache Dubbo Component
Java SDK (apache/dubbo)
### Details
In my caseļ¼ i need some thing to pass concurrency counter from request to
response.
```mermaid
graph TB
subgraph sync_same_reference
A[request1] -->|concurrency +1| B[invoker1]
B --> |concurrency -1|C[request2]
C-->|currency+1|D[invoker2]
D-->|currency-1|E[reference]
end
subgraph async
D[request1] -->|concurrency +1| E[invoker1]
H[request2] -->|concurrency +1| I[invoker2]
F[response1] --> |concurrency -1|G[Reference]
J[response2] --> |concurrency -1|K[Reference]
end
```
i use invocation.attribute to save this concurrencyCounter.
it work well in almost case. but in case 'MergeableClusterInvoker'
org.apache.dubbo.rpc.cluster.support.MergeableClusterInvoker#doInvoke
```java
Map<String, Result> results = new HashMap<>();
for (final Invoker<T> invoker : invokers) {
RpcInvocation subInvocation = new RpcInvocation(invocation,
invoker);
subInvocation.setAttachment(Constants.ASYNC_KEY, "true");
try {
results.put(invoker.getUrl().getServiceKey(),
invokeWithContext(invoker, subInvocation));
} catch (RpcException
```
as invocation reused attribute, the [last] async call back response may
decrease concurrency count for [next] request.
org.apache.dubbo.rpc.cluster.support.BroadcastClusterInvoker#doInvoke create
attribte by it self.
```java
try {
RpcInvocation subInvocation = new RpcInvocation(
invocation.getTargetServiceUniqueName(),
invocation.getServiceModel(),
invocation.getMethodName(),
invocation.getServiceName(),
invocation.getProtocolServiceKey(),
invocation.getParameterTypes(),
invocation.getArguments(),
invocation.copyObjectAttachments(),
invocation.getInvoker(),
Collections.synchronizedMap(new
HashMap<>(invocation.getAttributes())),
invocation instanceof RpcInvocation ? ((RpcInvocation)
invocation).getInvokeMode() : null);
```
some similar use case in
`org.apache.dubbo.rpc.filter.ActiveLimitFilter#getElapsed` may encounter same
problem.
should it use an other api for pass attribute or optimise rpcInvokcation
recreate logic
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GitHub link: https://github.com/apache/dubbo/discussions/15427
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