@Override
    public void execute(
            final HttpRequest request,
            final AsyncEntityProducer entityProducer,
            final AsyncExecChain.Scope scope,
            final AsyncExecChain chain,
            final AsyncExecCallback asyncExecCallback) throws HttpException, IOException {
        final String exchangeId = scope.exchangeId;
        final HttpRoute route = scope.route;
        final CancellableDependency operation = scope.cancellableDependency;
        final HttpClientContext clientContext = scope.clientContext;
        final AsyncExecRuntime execRuntime = scope.execRuntime;

        if (LOG.isDebugEnabled()) {
            LOG.debug("{} executing {} {}", exchangeId, request.getMethod(), request.getRequestUri());
        }

        final AsyncClientExchangeHandler internalExchangeHandler = new AsyncClientExchangeHandler() {

            private final AtomicReference<AsyncDataConsumer> entityConsumerRef = new AtomicReference<>();

            @Override
            public void releaseResources() {
                final AsyncDataConsumer entityConsumer = entityConsumerRef.getAndSet(null);
                if (entityConsumer != null) {
                    entityConsumer.releaseResources();
                }
            }

            @Override
            public void failed(final Exception cause) {
                final AsyncDataConsumer entityConsumer = entityConsumerRef.getAndSet(null);
                if (entityConsumer != null) {
                    entityConsumer.releaseResources();
                }
                execRuntime.markConnectionNonReusable();
                asyncExecCallback.failed(cause);
            }

            @Override
            public void cancel() {
                failed(new InterruptedIOException());
            }

            @Override
            public void produceRequest(final RequestChannel channel, final HttpContext context) throws HttpException, IOException {
                clientContext.setRequest(request);
                clientContext.setRoute(route);
                httpProcessor.process(request, entityProducer, clientContext);

                channel.sendRequest(request, entityProducer, context);
            }

            @Override
            public int available() {
                return entityProducer.available();
            }

            @Override
            public void produce(final DataStreamChannel channel) throws IOException {
                entityProducer.produce(channel);
            }

            @Override
            public void consumeInformation(final HttpResponse response, final HttpContext context) throws HttpException, IOException {
            }

            @Override
            public void consumeResponse(
                    final HttpResponse response,
                    final EntityDetails entityDetails,
                    final HttpContext context) throws HttpException, IOException {

                clientContext.setResponse(response);
                httpProcessor.process(response, entityDetails, clientContext);

                entityConsumerRef.set(asyncExecCallback.handleResponse(response, entityDetails));
                if (entityDetails == null) {
                    execRuntime.validateConnection();
                    asyncExecCallback.completed();
                }
            }

            @Override
            public void updateCapacity(final CapacityChannel capacityChannel) throws IOException {
                final AsyncDataConsumer entityConsumer = entityConsumerRef.get();
                if (entityConsumer != null) {
                    entityConsumer.updateCapacity(capacityChannel);
                } else {
                    capacityChannel.update(Integer.MAX_VALUE);
                }
            }

            @Override
            public void consume(final ByteBuffer src) throws IOException {
                final AsyncDataConsumer entityConsumer = entityConsumerRef.get();
                if (entityConsumer != null) {
                    entityConsumer.consume(src);
                }
            }

            @Override
            public void streamEnd(final List<? extends Header> trailers) throws HttpException, IOException {
                final AsyncDataConsumer entityConsumer = entityConsumerRef.getAndSet(null);
                if (entityConsumer != null) {
                    entityConsumer.streamEnd(trailers);
                } else {
                    execRuntime.validateConnection();
                }
                asyncExecCallback.completed();
            }

        };

        if (LOG.isDebugEnabled()) {
            operation.setDependency(execRuntime.execute(
                    exchangeId,
                    new LoggingAsyncClientExchangeHandler(LOG, exchangeId, internalExchangeHandler),
                    clientContext));
        } else {
            operation.setDependency(execRuntime.execute(exchangeId, internalExchangeHandler, clientContext));
        }
    }
Usually the last HTTP/2 request execution handler in the asynchronous
request execution chain that is responsible for execution of
request / response exchanges with the opposite endpoint.

@since 5.0
httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/H2AsyncMainClientExec.java