Hi Thuy,
Your code doesn't work because it tries to use nested WaitScopes. When a
server-side method is called, the event loop is already running, so you
have to use promise.then(lambda) instead of promise.wait(waitScope).
So instead of this:
auto& waitScope = ezClient2.getWaitScope();
{
auto request = client2.functionSampleRequest(); //Request to SERVER2
request.setIn(222);
auto promise = request.send();
promise.wait(waitScope);
}
return kj::READY_NOW;
Try:
auto request = client2.functionSampleRequest(); //Request to SERVER2
request.setIn(222);
return request.send()
.then([context](capnp::Response
response) {
// You can handle the response from server2 here if you want.
// If there's nothing to do, you can replace `.then()` with
`.ignoreResult()`.
})
-Kenton
On Mon, Sep 12, 2022 at 2:40 AM Thuy Doan wrote:
> Hi all,
>
> I am a newbie to CapnProto. I'd like to have your help.
>
> I want to request a function of server2 in the callback of server1.
> But I got an exception like below.
> Please help me resolve it.
> Many thanks!
>
> * thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
> (code=1, address=0x30020)
> * frame #0: 0x00010035859c
> libcapnp-rpc-0.10.2.dylib`capnp::VatNetwork capnp::rpc::twoparty::ProvisionId, capnp::rpc::twoparty::RecipientId,
> capnp::rpc::twoparty::ThirdPartyCapId,
> capnp::rpc::twoparty::JoinResult>::baseConnect(capnp::AnyStruct::Reader) + 20
> frame #1: 0x000100361a2c
> libcapnp-rpc-0.10.2.dylib`kj::_::TransformPromiseNode kj::Own, capnp::EzRpcClient::Impl::Impl(kj::StringPtr,
> unsigned int, capnp::ReaderOptions)::'lambda'(kj::Own&&),
> kj::_::PropagateException>::getImpl(kj::_::ExceptionOrValue&) + 512
> frame #2: 0x0001004d2220
> libkj-async-0.10.2.dylib`kj::_::RunnableImpl::run()
> + 32
> frame #3: 0x00010028aaa4
> libkj-0.10.2.dylib`kj::_::runCatchingExceptions(kj::_::Runnable&) + 40
> frame #4: 0x0001004c7e48
> libkj-async-0.10.2.dylib`kj::_::TransformPromiseNodeBase::get(kj::_::ExceptionOrValue&)
> + 64
> frame #5: 0x0001004c8684
> libkj-async-0.10.2.dylib`kj::_::ForkHubBase::fire() + 60
> frame #6: 0x0001004c654c
> libkj-async-0.10.2.dylib`kj::_::waitImpl(kj::Own&&,
> kj::_::ExceptionOrValue&, kj::WaitScope&, kj::SourceLocation) + 608
> frame #7: 0x00015198
> client`kj::Promise
> >::wait(kj::WaitScope&, kj::SourceLocation) + 120
> frame #8: 0x00014b94 client`main + 344
> frame #9: 0x00010003d08c dyld`start + 520
>
> *Sample source code as below*
>
> *SampleServer1.capnp:*
>
> interface SampleServer1 {
>
> callbackRegister @0 (callback :Callback) -> (); //to register a callback
>
> interface Callback {
> calbackFunc @0 (in :Int32) -> ();
> }
> }
>
> *SampleServer1::Server Impl:*
>
> class SampleServer1Impl : public SampleServer1::Server
> {
> ::kj::Promise callbackRegister(CallbackRegisterContext context){
> auto cb = context.getParams().getCallback());
>
> auto request = cb.calbackFuncRequest(); //Call callback function
> request.setIn(111);
> auto promise = request.send();
>
> return kj::READY_NOW;
> }
> }
>
> *SampleServer1::Callback::Server Impl:*
>
> class CallbackImpl : public SampleServer1::Callback::Server
> {
> ::kj::Promise calbackFunc(CalbackFuncContext context){
>
> capnp::EzRpcClient ezClient2("unix:/tmp/capnp-server-2");
> Server2::Client client2 = ezClient2.getMain();
>
> auto& waitScope = ezClient2.getWaitScope();
> {
> auto request = client2.functionSampleRequest(); //Request to SERVER2
> request.setIn(222);
> auto promise = request.send();
>
> promise.wait(waitScope);
>
> }
>
> return kj::READY_NOW;
> }
> }
>
> *SampleServer2.capnp:*
>
> interface SampleServer2 {
>
> functionSample @0 (in :Int32) -> ();
> }
>
> *SampleServer2::Server impl*
>
> class SampleServer2 Impl : public SampleServer2::Server
> {
> ::kj::Promise functionSample(FunctionSampleContext context){
> //Do something
> return kj::READY_NOW;
> }
> }
>
> *Client implement*
>
> capnp::EzRpcClient ezClient("unix:/tmp/capnp-server-1");
> Subscriber::Client client = ezClient.getMain();
> auto& waitScope = ezClient.getWaitScope();
>
> ::SampleServer1::Callback::Client callback =
> ::SampleServer1::Callback::Client(kj::heap());
>
> auto request = client.callbackRegisterRequest(); //Register a callback
> to Server1
> request.setCallback(callback);
> auto promise = request.send();
>
>
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