Sending data to SpatialOS

#include <improbable/standard_library.h>
        #include <improbable/worker.h>
        #include <example.h>
        
        using namespace improbable;

Use the worker::Connection to send data such as component updates, logs, and metrics to SpatialOS.

Component updates

Sending component updates

When the worker has authority over a component for some entity, it can send component updates for that component to SpatialOS. Do this using the worker::Connection method SendComponentUpdate<T> which takes a reference to a T::Update object. The template parameter T should be a component metaclass from the schema-generated code.

A component update can modify the value of a property or trigger an event. You can modify multiple properties and trigger multiple events in the same component update.

Component updates sent by the worker will appear in the operation list returned by a subsequent call to Connection::GetOpList. This means that OnComponentUpdate callbacks will also be invoked for component updates triggered by the worker itself, but not immediately.

There are a couple of (related) reasons that callbacks for sent component updates should not be invoked immediately:

• This can lead to extremely unintuitive control flow when components are recursively updated inside a callback
• It violates the guarantee that callbacks are only invoked as a result of a call to Process<T> method on the worker::Dispatcher.

Sending and receiving component events

Sending and receiving events works much in the same way as component updates. For a schema like the following:

package example;
        
        type SwitchToggled {
          int64 time = 1;
        }
        
        component Switch {
          id = 1234;
          bool is_enabled = 1;
          event SwitchToggled toggled;
        }

To trigger an event:

void TriggerEvent(worker::Connection& connection, worker::EntityId entity_id) {
          example::Switch::Update update;
          example::SwitchToggled event{1};
          update.add_toggled(event);
          connection.SendComponentUpdate<example::Switch>(entity_id, update);
        }

If you are not authoritative on the component, your event will be silently ignored.

Receiving an event works just like receiving a component update, by registering a callback on the dispatcher:

dispatcher.OnComponentUpdate<example::Switch>(
            [&](const worker::ComponentUpdateOp<example::Switch>& op) {
              // `op.Update.toggled()` contains a list of SwitchToggled events.
              for (auto it : op.Update.toggled()) {
                std::cout << "Switch toggled at " << it.time() << std::endl;
              }
            });

Receiving component updates

To be notified when a worker receives a component update on an entity in the worker’s local view of the simulation, use the worker::Dispatcher method OnComponentUpdate with the same template paramater T as for sending updates.

Note that the component updates:

• can be partial, i.e. only update some properties of the component
• do not necessarily have to contain data that is different from the worker’s current view of the component
• could have been sent by SpatialOS rather than a worker for synchronization purposes

Updating component interests

For each entity in its view, a worker receives updates for (“has interest in”):

• the set of components the worker has authority over
• the set of components it is explicitly interested in

A worker always has interest in the components of the entities it is authoritative on, in addition to any others specified in the bridge settings or using the method described below.

You can configure the set of explicitly interested components in the bridge settings. This is the default set of explicit interest for every entity.

At runtime, the worker can override this set on a per-entity, per-component basis, using the Connection::SendComponentInterest method.

When the set of interested components for an entity changes, the worker receives the appropriate OnAddComponent and OnRemoveComponent callbacks to reflect this change.

For example, you might be interested in one specific switch, but not every switch in the world:

void ComponentInterest(worker::Connection& connection, worker::EntityId entity_id) {
          connection.SendComponentInterest(
              entity_id,
              {{example::Switch::ComponentId, worker::InterestOverride{/* IsInterested */ true}}});
        }

Component commands

Sending component commands

To send a command request, use the worker::Connection method SendCommandRequest<T>. The command is executed by the worker that currently has authority over the component containing the command on the entity specified in the command request.

SendCommandRequest<T> takes:

• an entity ID
• an optional timeout
• a T::Request object

• an optional CommandParameters object

  This contains a field called AllowShortCircuit, which, if set to true, will try to “short-circuit” the command and avoid a round trip to SpatialOS in some cases. See documentation on commands for more information.

• The template parameter T should be a command metaclass defined in the schema-generated code.

Before sending the command, register a callback to handle the response with the worker::Dispatcher with OnCommandResponse<T>. You can match up the request ID returned by SendCommandRequest (of type worker::RequestId<worker::OutgoingCommandRequest<T>>) with the one in the CommandResponseOp to identify the request that is being responded to.

Command failures

Commands can fail, so you should check the StatusCode field in the CommandResponseOp, and retry the command as necessary. The caller will always get a response callback, but it can be one of several failure cases, including:

• ApplicationError (rejected by the target worker or by SpatialOS)
• AuthorityLost (target worker lost authority, or no worker had authority)
• NotFound (target entity, or target component on the entity, didn’t exist)
• PermissionDenied (sending worker didn’t have permission to send request)
• Timeout
• InternalError (most likely indicates a bug in SpatialOS, should be reported)

For more detail on these status codes, see the documentation for StatusCode.

Receiving component commands

To handle commands issued by another worker, use the opposite flow:

1. Register a callback with the worker::Dispatcher with OnCommandRequest<T>.

2. When the callback is executed:

   • To respond to the command, call the Connection method SendCommandResponse<T>. Supply the request ID (of type worker::RequestId<worker::IncomingCommandRequest<T>>) provided by the worker::CommandRequestOp and an appropriate T::Response response object.

   • To fail the command, call SendCommandFailure<T>.

Note that a RequestId only uniquely identifies a single command invocation from the perspective of a single worker; that is, the RequestId used by the calling worker and the RequestId used by the caller worker for handling that same command are unrelated.

Entity queries

A worker can run remote entity queries against the simulation by using the Connection method SendEntityQueryRequest. This takes a worker::query::EntityQuery object and an optional timeout.

Like other request methods, this returns a worker::RequestId, which can be used to match a request with its response.

The query object

The query object is made of

• an worker::query::Constraint, which determines which entities are matched by the query.

  Available constraints:

  • EntityIdConstraint: Matches a specific entity ID.
  • ComponentConstraint: Matches entities with a particular component.
  • SphereConstraint: Matches entities contained in the given sphere.
  • AndConstraint: Matches entities that match all of the given subconstraints.
  • OrConstraint: Matches entities that match any of the given subconstraints.
  • NotConstraint](/reference/13.1/cppsdk/api-reference#worker-query-not_constraint): Matches entities that do not match the given subconstraint.

• An worker::query::ResultType, which determines what data is returned for matched entities.

  Available result types:

  • CountResultType: Returns the number of entities that matched the query.

  • SnapshotResultType: Returns a snapshot of component data for entities that matched the query.

    To select all components, use worker::query::SnapshotResultType snapshotResultType{{}};.

    To select every component whose ID is contained in the given set, use worker::query::SnapshotResultType snapshotResultType{{componentIdSet}}; (thus, pass an empty set to get no components but entity IDs only).

The query response

The response is received via a callback registered with the worker::Dispatcher using the OnEntityQueryResponse method.

The EntityQueryResponseOp contains:

• a std::size_t ResultCount field (forCountResultType requests)
• a Map<EntityId, Entity> (for SnapshotResultType) requests.

Success or failure of the request is indicated by the StatusCode field of the response object, but in the failure case the result may still contain some data: the count or snapshot map might still contain the data for some entities that matched the query, but won’t necessarily contain all matching entities. This is because the worker might still be able to do something useful with a partial result.

Sending and receiving metrics

You can optionally send metrics by calling Connection::SendMetrics. You can view metrics by going to the Inspector World view and clicking on a worker.

There are two typical use cases for sending metrics:

1. Reporting your own custom metrics. Both time series and histogram metrics are supported.

2. Updating a worker’s load when the worker is using dynamic load balancing.

   The load of a worker is a floating-point value, with 0 indicating an unloaded worker and values above 1 corresponding to an overloaded worker. The reported values direct SpatialOS’s load balancing strategy.

Example

The following example demonstrates both use cases:

// A queue of tasks the worker has to complete.
        std::queue<std::function<void()>> taskQueue;
        constexpr double kMaximumQueueSize = 200;  // An arbitrary maximum value.
        
        void SendUserMetrics(worker::Connection& connection) {
          worker::Metrics metrics;
          // Update the current load of the worker.
          double load = static_cast<double>(taskQueue.size()) / kMaximumQueueSize;
          metrics.Load = load;
        
          // Update the custom metrics.
          metrics.GaugeMetrics["MyCustomMetric"] = 1.0;
          worker::HistogramMetric histogram_metric{};
          histogram_metric.RecordObservation(123);
          metrics.HistogramMetrics["MyHistogramMetric"] = histogram_metric;
        
          connection.SendMetrics(metrics);
        }

Workers automatically send several built-in, internal gauge metrics at a period defined by the BuiltInMetricsReportPeriodMillis field of worker::ConnectionParameters. You can register a callback to receive these metrics inside a worker::MetricsOp using Dispatcher::OnMetrics:

void RegisterMetricsCallback(worker::Dispatcher& dispatcher) {
          dispatcher.OnMetrics([&](const worker::MetricsOp& op) {
            auto short_circuit_rate =
                op.Metrics.GaugeMetrics.find("connection_command_request_short_circuit_rate");
            // Do something with the metric, or store it...
            std::cout << "Command requests short-circuited per second: " << short_circuit_rate->second
                      << std::endl;
          });
        }

The full list of built-in gauge metrics is as follows. All rate metrics are per-second.

Sending logs

You can send log messages by calling Connection::SendLogMessage. Log messages can be viewed on deployment dashboards.

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