Subscriber's message handler wasn't called after leaving the try block

[Alan-Kuan]

Hi,

I wrote a simple pub/sub program in zenoh-cpp.
I found that a subscriber's message handler wasn't called after leaving the try block if it was declared inside one.
I'm not sure if this was a bug or that I just misunderstood the usage.

Here's the relevant code segment of the subscriber:

void runAsSubscriber(const char* conf_path) {
    try {
        auto config = zenoh::expect<zenoh::Config>(zenoh::config_from_file(conf_path));
        auto session = zenoh::expect<zenoh::Session>(zenoh::open(std::move(config)));
        auto subscriber = zenoh::expect<zenoh::Subscriber>(session.declare_subscriber(
            "my/topic", messageHandler
        ));

        std::getchar();  // I should put the function call here
    } catch (const zenoh::ErrorMessage& ex) {
        std::cerr << "Zenoh: " << ex.as_string_view() << std::endl;
        exit(1);
    }

    std::getchar();  // If I put it here, the handler wouldn't get called
}

void messageHandler(const zenoh::Sample& sample) {
    std::cout << "Received" << std::endl;
}

Any ideas? Thanks.

[milyin]

Hi @Alan-Kuan !

After leaving the try {} block both the session and subsriber are automatically destroyed as they left the lexical scope. You may use std::unique_ptr or just declare unitialized session and subscriber outside the block, using null constructors:

void runAsSubscriber(const char* conf_path) {
    zenoh::Session session(std::nullptr);
    zenoh::Subscriber subscriber(std::nullptr);
    try {
        auto config = zenoh::expect<zenoh::Config>(zenoh::config_from_file(conf_path));
        session = zenoh::expect<zenoh::Session>(zenoh::open(std::move(config)));
        subscriber = zenoh::expect<zenoh::Subscriber>(session.declare_subscriber(
            "my/topic", messageHandler
        ));

        std::getchar();  // I should put the function call here
    } catch (const zenoh::ErrorMessage& ex) {
        std::cerr << "Zenoh: " << ex.as_string_view() << std::endl;
        exit(1);
    }

    std::getchar();  // If I put it here, the handler wouldn't get called
}

void messageHandler(const zenoh::Sample& sample) {
    std::cout << "Received" << std::endl;
}

[Alan-Kuan]

Oh! I got it. Thank you.