This is expected. The KJ event loop runs when you call `.wait()`. The event
loop checks for network events and delivers callbacks. If you haven't
called .wait(), then the event loop has no way to run. KJ does not create
any background threads for this purpose; the thread that created the event
loop must call .wait() on a promise in order to run it. Usually, large
programs will actually have a single top-level `.wait()` call that runs the
entire program -- this might literally be `kj::NEVER_DONE.wait(waitScope)`
to wait forever. In such programs, all actual work is done in `.then()`
callbacks.
If you need to be able to receive KJ events at the same time as executing
other code (especially bulk CPU-heavy work), then you will have to create a
separate thread yourself, and figure out how to communicate between them.
The KJ event loop is tied to a specific thread and cannot be directly
accessed from other threads; however, you can use the `kj::Executor`
interface to schedule work on another thread's event loop, or
kj::newPromiseAndCrossThreadFulfiller() to create a promise/fulfiller pair
that can be fulfilled from a different thread.
-Kenton
On Tue, Oct 17, 2023 at 6:37 AM Bhavya R <bhavyar.1...@gmail.com> wrote:
> Hello All,
>
> I am trying to pass client capability to sever, client should receive
> notify back on any updates.
> In my application, Service is sending statusHearbeat continuously, but
> client receives callback only when it is waiting on any promise. Could
> anyone please guide on how to receives callback from server? My client
> application is running on windows.
>
> For e.g only duration when i am blocked on wait() call, i see callback
> gets received and dispatchCall is triggered
>
> This call is done from client -> server
> auto request = connect->directorRef->versionRequest();
> auto responsePromise = request.send();
> auto response = *responsePromise.wait(*
> connect->clientRef->getWaitScope());
>
> e.g interface FaTfServerToClient {
> statusHeartbeat @0 () -> ();
> }
>
> interface FaTfClientToServer {
> version @0 () -> (version :Base.Version);
> }
>
> Client connection---> I am passing client bootstrap TransformEventHandler
> object
>
>
> auto address = connect->ioContext.provider->getNetwork()
> .parseAddress(ipAddress,
> port).wait(connect->ioContext.waitScope);
> connect->connection =
> address->connect().wait(connect->ioContext.waitScope);
> connect->clientRef =
> std::make_shared<capnp::TwoPartyClient>(*(connect->connection), kj::heap<
> *TransformEventHandler*>(observer),
> capnp::schemas::Side_9fd69ebc87b9719c::CLIENT);
> connect->directorRef =
> std::make_shared<FaTfClientToServer::Client>(connect->clientRef->bootstrap().castAs<
> FaTfClientToServer >());
>
>
> *class TransformEventHandler : public FaTfServerToClient::Server, public
> EventHandler {*
> ::kj::Promise<void> statusHeartbeat(StatusHeartbeatContext context)
> override {
> std::cout << "status heartbeat" << std::endl;
> return kj::READY_NOW;
> }
> }
>
> I tried adding another iocontext, client in different thread and ran
> wait() on that. It doesnt receive nothing.
> Looks like i haven't understood basic mechanism!! Any pointers would be
> very helpful. Thanks
>
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