The contents of a stasher::heartbeat object
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The contents of a stasher::heartbeat object

typedef stasher::heartbeat<application_id,status_class> heartbeat;

typedef stasher::heartbeatptr<application_id,status_class> heartbeatptr;

heartbeat hb_instance=heartbeat::create( ... );

// ...

hb_instance::base::lock lock(*hb_instance);

stasher::current_heartbeatptr<application_id,status_class> ptr=lock->value;

if (!ptr.null())
{
    stasher::current_heartbeat<application_id,status_class> ref=ptr;

    stasher::current_heartbeat<application_id,status_class>::base::timestamps_t &timestamps=ref->timestamps;

    for (auto &map_entry:timestamps)
    {
        const application_id &instance=map_entry.first;

        const stasher::heartbeat_meta_t<status_class> &meta=map_entry.second;

        time_t timestamp=meta.timestamp;
        const status_class &status=meta.second;
        // Unless status_class is void
    }
}

This is a synopsis of the contents of stasher::heartbeat. It is based on a versioned current object. It is a reference-counted object. stasher::heartbeat defines a reference, and stasher::heartbeatptr is a nullable pointer reference.

Constructing an instance of the lock acquires an exclusive lock on the reference-counted stasher::current_heartbeatptr value. This is a nullable reference pointer. As explained in the section called “Versioned current objects” it's null immediately after the heartbeat object gets constructed, until the current value of the heartbeat object gets retrieved from the object repository.

Note

lock acquires an exclusive lock on the object, preventing it from getting updated by the client connection thread if the object gets updated in the repository. The lock object must be initiated on the stack, and it should not be held for an extensive period of time.

If it's not null, it's a stasher::current_heartbeat, and it contains the usual stasher uuid, maintained by the versioned current object template, and a single member, varname, which is a stasher::current_heartbeat<application_id,status_class>::base::timestamps_t.

This is a std::map that can be iterated over, keyed by application_id. The map's value is a stasher::heartbeat_meta_t<status_class> which contains two members, status, which is application_id's most recent posted hearbeat status, and timestamp, giving the time that this posted status expires.

A void status_class results in a stasher::heartbeat_meta_t with just a timestamp.

The heartbeat update functor gets invoked each time the manager updates the heartbeat object (and in other cases too). After constructing a new heartbeat object, the application should wait for the first call the update functor in order to read the initial heartbeat status of other application instances. 

hb->admin_drop(application_id("listener"),
                  []
                  (bool success, const std::string &message)
                  {
                  });

admin_drop() removes another instance's posted status if it is expired, but not yet stale enough to get removed. The first parameter is an application_id() whose status should be removed, the second parameter is a functor.

The functor takes two arguments, a bool and a std::string. The functor gets invoked when the request gets processed. This can happen before admin_drop() return or after, depending on whether the request gets immediately rejected, or not.

The bool value indicates whether the request succeded and the instance's status was removed, or not. In all cases, the std::string parameter is a descriptive message. 

hb->report(std::cout);

report() produces a summary of the current status of the heartbeat object, and writes it to the given output stream.

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A heartbeat example Table Of Contents Part III. Command Documentation