Using the C++ worker SDK
Overview
The most important units of functionality in the C++ worker API are:
- The
worker::Locator
, which is responsible for querying for and connecting to remote cloud deployments. - The
worker::Connection
, which represents a worker’s connection to a SpatialOS simulated world. - The
worker::Dispatcher
, which is responsible for invoking user-provided callbacks based on data received from SpatialOS via theworker::Connection
. - The
worker::Entity
, which is a container for the component data associated with a single entity. - The
worker::View
, which is an optional drop-in replacement for theworker::Dispatcher
that additionally maintains a map from entity ID toworker::Entity
.
For the full API reference, have a look at <improbable/worker.h>
.
Connecting to SpatialOS
Before it can interact with the simulated world, the worker must connect to SpatialOS.
There are two ways of doing this:
- Instantiate a
worker::Connection
object directly. This allows to connect a managed worker (i.e running in the cloud and started by the SpatialOS runtime) or a remote worker used for debugging via ([spatial cloud connect external](/reference/11.0/tools/spatial/spatial-cloud-connect-external)
). The connection is made through the receptionist service of the targeted deployment for which the IP and port should be passed as arguments to the worker. These values can be filled-in automatically at runtime by using theIMPROBABLE_RECEPTIONIST_HOST
andIMPROBABLE_RECEPTIONIST_PORT
placeholders in your worker’s launch configuration. - Use the
worker::Locator
object to enumerate cloud deployments and connect to a chosen deployment with authentication. This is typically used to connect an external client to a cloud deployment.
The value given for the UseExternalIp
field in the NetworkParameters
structure is also relevant.
The table below summarizes the connection possibilities:
Using worker::Connection directly |
Using worker::Locator |
|
---|---|---|
UseExternalIp == true |
Local client connecting via spatial cloud connect external proxy |
External client connecting to cloud deployment |
UseExternalIp == false |
Managed cloud worker; local client connecting to local deployment | N/A |
The example below illustrates a very basic connection setup, where the worker takes three command-line arguments specifying the worker’s own ID as well as the receptionist’s IP and port. It will use TCP and connect using the internal IP address.
int main(int argc, char** argv) {
if (argc != 4) {
return 1;
}
worker::ConnectionParameters parameters;
parameters.WorkerType = "MyCPlusPlusWorker";
parameters.Network.ConnectionType = worker::NetworkConnectionType::kTcp;
parameters.Network.UseExternalIp = false;
const std::string workerId = argv[1];
const std::string hostname = argv[2];
const std::uint16_t port = static_cast<std::uint16_t>(std::stoi(argv[3]));
worker::Connection connection = worker::Connection::ConnectAsync(hostname, port, workerId, parameters).Get();
...
}
Note that worker::Connection
objects are not thread-safe.
Handling data received from SpatialOS
It is up to each worker to decide how the basic event loop should be structured, depending on its
requirements. The worker should call worker::Connection::GetOpList
to get a list of “operations”
(for example a new entity, or a component update) from SpatialOS that have been sent since the last time
the function was called. This worker::OpList
then needs to be passed to a dispatcher in order to
invoke user-provided callbacks.
The following snippet shows a (very) simple example implementation of an event loop that processes operations from SpatialOS 60 times per second:
#include <improbable/worker.h>
#include <chrono>
#include <thread>
void RunEventLoop(worker::Connection& connection, worker::Dispatcher& dispatcher) {
static const unsigned kFramesPerSecond = 60;
static const std::chrono::duration<double> kFramePeriodSeconds(1. / static_cast<double>(kFramesPerSecond));
auto time = std::chrono::high_resolution_clock::now();
while (true) {
auto op_list = connection.GetOpList(0 /* non-blocking */);
// Invoke user-provided callbacks.
dispatcher.Process(op_list);
// Do other work here...
time += kFramePeriodSeconds;
std::this_thread::sleep_until(time);
}
}
Note that all callbacks provided to the
worker::Dispatcher
will be invoked only when worker::Dispatcher::Process
is called, and only
on the thread that is currently calling worker::Dispatcher::Process
: the user has complete
control over callback timing and threading decisions.
If the connection fails (when Connection.IsConnected() == false
), any error messages explaining the cause
will be returned by GetOpList(). Make sure to process this list in order to receive all
available diagnostic information.
Dispatcher callbacks
Several kinds of callbacks can be registered on the worker::Dispatcher
. Each method takes an
arbitrary callable std::function<void(const Param&)>
, where the parameter type Param
depends on
the particular kind of callback being registered. The following table has the details:
Method | Parameter type (and fields) | Invoked when… |
---|---|---|
OnDisconnect |
worker::DisconnectOp (std::string Reason ) |
the Connection is no longer connected and can no longer be used. Check the log for errors relating to the disconnection. |
OnLogMessage |
worker::LogMessageOp (worker::LogLevel Level , std::string Message ) |
the SDK issues a log message for the worker to print. This does not include messages sent using Connection.SendLogMessage . |
OnMetrics |
worker::MetricsOp (worker::Metrics Metrics ) |
the SDK reports built-in internal metrics. |
OnCriticalSection |
worker::CriticalSectionOp (bool InCriticalSection ) |
a critical section is about to be entered or has just been left. |
OnAddEntity |
worker::AddEntityOp (worker::EntityId EntityId ) |
an entity is added to the worker’s view of the simulation. |
OnRemoveEntity |
worker::RemoveEntityOp (worker::EntityId EntityId ) |
an entity is removed from the worker’s view of the simulation. |
OnReserveEntityIdResponse |
worker::ReserveEntityIdResponseOp (worker::RequestId<worker::ReserveEntityIdRequest> RequestId , worker::StatusCode StatusCode , std::string Message , Option<worker::EntityId> EntityId ) |
the worker has received a response for an entity ID reservation it had requested previously. |
OnCreateEntityResponse |
worker::CreateEntityResponseOp (worker::RequestId<worker::CreateEntityRequest> RequestId , worker::StatusCode StatusCode , std::string Message , Option<worker::EntityId> EntityId ) |
the worker has received a response for an entity creation it had requested previously. |
OnDeleteEntityResponse |
worker::DeleteEntityResponseOp (worker::RequestId<DeleteEntityRequest> RequestId , worker::EntityId EntityId , worker::StatusCode StatusCode , std::string Message ) |
the worker has received a response for an entity deletion it had requested previously. |
OnEntityQueryResponse |
worker::EntityQueryResponseOp (worker::RequestId<EntityQueryRequest> RequestId , worker::StatusCode StatusCode , std::string Message , std::size_t ResultCount , worker::Map<worker::EntityId, worker::Entity> Result >) |
the worker has received a response for an entity query it had requested previously. |
OnAddComponent<T> |
worker::AddComponentOp<T> (worker::EntityId EntityId , T::Data Data ) |
a component is added to an existing entity in the worker’s view of the simulation. |
OnRemoveComponent<T> |
worker::RemoveComponentOp (worker::EntityId EntityId ) |
a component is removed from an existing entity in the worker’s view of the simulation. |
OnAuthorityChange<T> |
worker::AuthorityChangeOp (worker::EntityId EntityId , bool HasAuthority ) |
the worker is granted authority over an entity’s component, or the worker’s authority over an entity’s component is revoked. |
OnComponentUpdate<T> |
worker::ComponentUpdateOp<T> (worker::EntityId EntityId , T::Update Update ) |
a component for an entity in the worker’s view of the simulation has been updated. |
OnCommandRequest<T> |
worker::CommandRequestOp<T> (worker::RequestId<IncomingCommandRequest<T>> RequestId , worker::EntityId EntityId , std::uint32_t TimeoutMillis , std::string CallerWorkerId , List<std::string> CallerAttributeSet , T::Request Request ) |
the worker has received a command request for a component on an entity over which it has authority. |
OnCommandResponse<T> |
worker::CommandResponseOp<T> (worker::RequestId<OutgoingCommandRequest<T>> RequestId , worker::EntityId EntityId , worker::StatusCode StatusCode , Option<T::Response> Response ) |
the worker has received a command response for a request it issued previously. |
(Note that some callbacks use a template parameter T
which relates to schema-generated code. This is
discussed in more detail below.)
Here’s an example of registering callbacks:
void RegisterCallbacks(worker::Dispatcher& dispatcher) {
dispatcher.OnAddEntity([&](const worker::AddEntityOp& op) {
// Do something with op.EntityId
});
}
Of course, you don’t have to use lambdas:
void PositionUpated(const worker::ComponentUpdateOp<Position>& op) {
// Do something with op.EntityId and op.Position
}
void RegisterCallbacks(worker::Dispatcher& dispatcher) {
dispatcher.OnComponentUpdate<Position>(&PositionUpdated);
}
If you want to unregister a callback, call Remove()
with the Dispatcher::CallbackKey
returned from the registration method:
void RegisterAndUnregisterCallbacks(worker::Dispatcher& dispatcher) {
auto key = dispatcher.OnRemoveEntity(&EntityRemoved);
// ...
dispatcher.Remove(key);
}
Using the View
worker::View
is subclass of worker::Dispatcher
, which adds the functionality of automatically
maintaining the current state of the worker’s view of the simulated world. It has a field called
Entities
, which is a map from entity ID to worker::Entity
objects. When a View
processes an OpList
, it automatically updates the state of this map as appropriate. Any
user-defined callbacks are also invoked, as per the Dispatcher
contract.
Dispatcher invocation order
AddEntityOp
callbacks are invoked in the order they were registered with the worker::Dispatcher
,
while RemoveEntityOp
callbacks are invoked in reverse order. This means that pairs of add/remove
callbacks can correctly depend on resources managed by pairs of callbacks registered earlier. This
is similar to the usual C++ construction/destruction order. Similarly, AuthorityChangeOp
callbacks are invoked in the order they were registered when authority is granted, but in reverse
order when authority is revoked.
In particular, this invocation order has the side-effect that the final state of an entity removed
in a RemoveEntityOp
callback can still be inspected in the worker::View
.
Critical sections
The protocol supports the concept of critical sections. A critical section is a block of operations that should be processed atomically by the worker. For example, a set of entities representing a stack of cubes should be added to the scene in its entirety before any physics simulation is done.
The CriticalSectionOp
callback is invoked with InCriticalSection == true
just before
the first operation of the critical section is delivered, and is invoked again with
InCriticalSection == false
just after the last operation of the critical section is delivered.
Worker flags
To access the value of a worker flag, use the GetWorkerFlag
method
of a Connection
:
Option<std::string> GetWorkerFlag(const std::string& flag_name) const;
For example:
auto work_speed_flag = connection->GetWorkerFlag("mycompany_theproject_work_speed");
if (work_speed_flag) {
SetWorkSpeed(*work_speed_flag);
} else {
SetDefaultWorkSpeed();
}
Sending data to SpatialOS
A worker can send data such as logging, metrics, and component updates to SpatialOS using the
worker::Connection
.
Logging and metrics
The worker::Connection
has two methods to send diagnostic information to SpatialOS:
SendLogMessage
, which is used for distributed logging, and SendMetrics
, which updates timeseries
and histogram data associated with this worker. Logs and metrics are available on deployment
dashboards.
The Connection
periodically reports several built-in internal metrics using worker::MetricsOp
,
which you would usually want to send to SpatialOS along with your custom metrics. It might look
something like this:
worker::Metrics metrics;
metrics.GaugeMetrics["MyCustomMetric"] = 1.0;
dispatcher.OnMetrics([&](const worker::MetricsOp& op) {
// Fill in the SDK built-in metrics.
metrics.Merge(op.Metrics);
connection.SendMetrics(metrics);
});
The worker::Metrics
structure should also be used to set the worker load when using
dynamic load balancing
for a worker. 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. An example of load reporting could be:
worker::Metrics metrics;
std::queue<Task> taskQueue;
double kMaximumQueueSize = 200; // An arbitrary maximum value.
dispatcher.OnMetrics([&](const worker::MetricsOp& op) {
// Update the current load of the worker
metrics.Load = (static_cast<double>(taskQueue.size()) / kMaximumQueueSize);
// Combine with the SDK built-in metrics and send to SpatialOS.
metrics.Merge(op.Metrics);
connection.SendMetrics(metrics);
});
// Main-event loop
while (true) {
// Process tasks from the taskQueue.
}
Sending and receiving component updates
When the worker has authority over a particular component for some entity, it can send component
updates to SpatialOS. This is done using the worker::Connection
method
SendComponentUpdate<T>
which takes a reference to a T::Update
object. The template parameter T
should be component metaclass in the schema-generated code. These are discussed further below.
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 worker::Connection::GetOpList
. This means that ComponentUpdateOp
callbacks will also be
invoked for component updates triggered by the worker itself, but not immediately.
There are several (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; and it violates the guarantee that callbacks are only invoked as a result
of a call to Process
method on the worker::Dispatcher
.
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 workers current view of the component, and could have been sent by SpatialOS rather than a worker
for synchronization purposes.
Sending and receiving component events
Sending and receiving events works much in the same way as component updates. For a schema like the following,
type SwitchToggled {
int64 time = 1;
}
component Switch {
id = 1234;
bool is_enabled = 1;
event SwitchToggled toggled;
}
triggering an event can be done as follows:
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) {
const example::Switch::Update& update = op.Update;
// `update.toggled()` contains a list of SwitchToggled events.
});
Sending component interests
For each entity in its view, a worker receives updates for a set of the entity’s components. This set is the union of the set of components the worker has authority over, and a set of components it is explicitly interested in.
The initial set of explicitly interested components can be configured 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, by using the Connection::SendComponentInterest
method.
Whenever the set of interested components for an entity changes, the worker will receive the appropriate
OnAddComponent
and OnRemoveComponent
callbacks to reflect this change.
For example, you might be interested in the local player’s inventory, but not the inventories of other players within the world:
dispatcher.OnAuthorityChange<PlayerControls>([&](const worker::AuthorityChangeOp& op) {
// If we have authority over this player's controls component, then the entity represents the local player.
if (op.HasAuthority) {
connection::SendComponentInterest(
op.EntityId,
{{Inventory::ComponentId, worker::InterestOverride{/* IsInterested */ true}}});
}
});
Note that a worker is always considered to be interested in the components of the entities it is authoritative on, in addition to any others specificed in the bridge settings or using the method described above.
Sending and receiving component commands
To send a command to be executed by the worker currently authoritative over a particular component
for a particular entity, use the worker::Connection
method SendCommandRequest<T>
. In this case the
template parameter T
should be a command metaclass defined in the schema-generated code. This
function takes an entity ID, an optional timeout, a T::Request
object and an optional
CommandParameters
object. The CommandParameters
object contains a field called
AllowShortCircuiting
, 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.
Before sending the command, a callback to handle the response should be registered with the
worker::Dispatcher
with OnCommandResponse<T>
. The worker::RequestId<worker::OutgoingCommandRequest<T>>
returned by SendCommandRequest
can be matched up with the one in the worker::CommandResponseOp
to identify the request that is being responded to.
Note that commands may fail, so the worker::StatusCode
field in the
worker::CommandResponseOp
should be checked, and the command can be retried 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)
To handle commands issued by another worker, the opposite flow is used. Register a callback with the
worker::Dispatcher
with OnCommandRequest<T>
; when the callback is executed, the worker should
make sure to call the worker::Connection
method SendCommandResponse<T>
, supplying the
worker::RequestId<worker::IncomingCommandRequest<T>>
provided by the worker::CommandRequestOp
and an appropriate T::Response
response object. Alternatively, the worker can call
SendCommandFailure<T>
to fail the command instead.
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
Note: In order to send an entity query, a worker must have permission to do so. For more information, see the Worker permissions page.
A worker can run remote entity queries against the simulation by using the worker::Connection
method SendEntityQueryRequest
. This takes a worker::query::EntityQuery
object and an optional timeout.
The query object is made of an worker::query::Constraint
and a worker::query::ResultType
.
The constraint determines which entities are matched by the query, and the result type determines what data is
returned for matched entities. Available constraints and result types are described below.
Constraint | Description |
---|---|
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 sub-constraints. |
OrConstraint |
Matches entities that match any of the given sub-constraints. |
Result type | Description |
---|---|
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). |
Important: You should keep entity queries as limited as possible. All queries hit the network and cause a runtime lookup, which is expensive even in the best cases. This means you should:
- always limit queries to a specific sphere of the world
- only return the information you need from queries (eg the specific components you care about)
- if you’re looking for entities that are within your worker’s checkout radius, search internally on the worker instead of using a query
Like other request methods, this returns a worker::RequestId
, which can be used to match a request with its
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 (for CountResultType
requests)
and a Map<EntityId, Entity>
(for SnapshotResultType
) requests. Again, 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.
Creating and deleting entities
Note: In order to create or delete an entity, a worker must have permission to do so. For more information, see the Worker permissions page.
A worker can request SpatialOS to reserve an entity ID, create an entity, or delete an entity,
by using the worker::Connection
methods SendReserveEntityIdRequest
, SendCreateEntityRequest
,
and SendDeleteEntityRequest
, respectively.
These methods return a worker::RequestId
, which can be used to match a request with its response. The response is
received via a callback registered with the worker::Dispatcher
using OnReserveEntityIdResponse
,
OnCreateEntityResponse
, and OnDeleteEntityResponse
, respectively.
Note that these operations may fail, so the StatusCode
field in the ReserveEntityIdResponseOp
,
CreateEntityResponseOp
, or DeleteEntityResponseOp
argument of the respective callback
should be checked, and the command can be retried as necessary. The caller will always get a response
callback, but it might be a timeout.
SendReserveEntityIdRequest
takes an optional timeout. If the operation succeeds, the response contains
an entity ID, which is guaranteed to be unused in the current deployment.
SendCreateEntityRequest
takes a worker::Entity
representing the initial state of the entity, an optional
entity ID (which, if provided, must have been obtained by a previous call to SendReserveEntityIdRequest
),
and an optional timeout. If the operation succeeds, the response contains the ID of the newly created entity.
SendDeleteEntityRequest
takes an entity ID and an optional timeout. The response contains no
additional data.
Example
Here’s an example of reserving an entity ID, creating an entity with that ID and some initial state, and finally deleting it:
const std::uint32_t kTimeoutMillis = 500;
// Reserve an entity ID.
worker::RequestId<worker::ReserveEntityIdRequest> entity_id_reservation_request_id
= connection->SendReserveEntityIdRequest(kTimeoutMillis);
// When the reservation succeeds, create an entity with the reserved ID.
worker::RequestId<worker::CreateEntityRequest> entity_creation_request_id;
dispatcher.OnReserveEntityIdResponse([&](const worker::ReserveEntityIdResponseOp& op) {
if (op.RequestId == entity_id_reservation_request_id && op.StatusCode == worker::StatusCode::kSuccess) {
// ID reservation was successful - create an entity with the reserved ID.
worker::Entity entity;
// Empty ACL - should be customised.
entity.Add<EntityAcl>({{{}}, {}});
// Needed for the entity to be persisted in snapshots.
entity.Add<Persistence>({});
entity.Add<Position>({{1, 2, 3}});
entity_creation_request_id = connection->SendCreateEntityRequest(entity, *op.EntityId, kTimeoutMillis);
}
});
// When the creation succeeds, delete the entity.
worker::RequestId<worker::DeleteEntityRequest> entity_deletion_request_id;
dispatcher.OnCreateEntityResponse([&](const worker::CreateEntityResponseOp& op) {
if (op.RequestId == entity_creation_request_id && op.StatusCode == worker::StatusCode::kSuccess) {
entity_deletion_request_id = connection->SendDeleteEntityRequest(*op.EntityId, kTimeoutMillis);
}
});
// When the deletion succeeds, we're done.
dispatcher.OnDeleteEntityResponse([&](const worker::DeleteEntityResponseOp& op) {
if (op.RequestId == entity_deletion_request_id && op.StatusCode == worker::StatusCode::kSuccess) {
// Test successful!
}
});
Entity ACLs
Entity ACLs are exposed to the worker as a component, and
can be manipulated as any other component. ACLs can be set at entity creation time, or modified
dynamically at runtime by the worker that has authority over the EntityAcl
component.
This example adds an EntityAcl
to an Entity
given a CommandRequestOp
, which is currently the only
way to make a specific worker (as opposed to, potentially, a set of workers) to qualify for authority of
a component. Specifically:
- The entity will be visible to workers that have the “client” or “physics” worker attribute.
- Any “physics” worker (i.e. a worker with “physics” as one of its attributes) can be authoritative over the
entity’s
Position
andEntityAcl
components. - The worker, which issued the
CommandRequestOp
, is the only worker that can be authoritative over thePlayerControls
component.
This can be used as part of creating a new entity in response to a command request.
template <typename C>
void AddComponentDelegations(const worker::CommandRequestOp<C>& op, worker::Entity& entity) {
// This requirement set matches only the command caller, i.e. the worker that issued the command,
// since attribute set includes the caller's unique attribute.
improbable::WorkerAttributeSet callerWorkerAttributeSet{op.CallerAttributeSet};
improbable::WorkerRequirementSet callerWorkerRequirementSet{{callerWorkerAttributeSet}};
// This requirement set matches any worker with the attribute "physics".
improbable::WorkerRequirementSet physicsWorkerRequirementSet{
worker::List<improbable::WorkerAttributeSet>{
{worker::List<std::string>{"physics"}}}};
// This requirement set matches any worker with the attribute "client" or "physics".
auto clientOrPhysicsRequirementSet = improbable::WorkerRequirementSet{{
improbable::WorkerAttributeSet{{"client"}},
improbable::WorkerAttributeSet{{"physics"}}
}};
// Give authority over Position and EntityAcl to any physics worker, and over PlayerControls to
// the caller worker.
worker::Map<worker::ComponentId, improbable::WorkerRequirementSet> componentWriteAcl = {
{Position::ComponentId, physicsWorkerRequirementSet},
{EntityAcl::ComponentId, physicsWorkerRequirementSet},
{PlayerControls::ComponentId, callerWorkerRequirementSet}
};
entity.Add<EntityAcl>(
EntityAcl::Data{/* read */ clientOrPhysicsRequirementSet, /* write */ componentWriteAcl});
}
The worker authoritative over the EntityAcl
component can later decide to give the authority over
position (or any other component) to a different worker, e.g. the client. In order to do this,
EntityAclData
needs to be modified in order to map Position::ComponentId
to callerWorkerRequirementSet
(created above). This change can be made using the method below:
// Take a copy of the EntityAclData argument, so that this method doesn't modify the original one.
EntityAclData DelegateComponent(EntityAclData acl, worker::ComponentId componentId,
const improbable::WorkerRequirementSet& requirementSet) {
// Set the write ACL for the specified component to the specified attribute set,
// assuming the componentAcl option is not empty.
acl.component_write_acl().emplace(componentId, requirementSet);
return acl;
}
For these changes to take effect, the worker authoritative over the EntityAcl
component needs send the changes
through a component update.
Please read Worker attributes and worker requirements for more information.
Generated code
The C++ schema-generated code consists of two main parts: data classes and component classes. Data
classes are used to represent data at rest and correspond to the schemalang type
definitions;
component classes correspond to schemalang component
definitions and contain metadata and classes
for sending and receiving component data (updates, command requests and command responses).
A data class will be generated for each type defined in the schema, with fields corresponding to each field in the schema definition.
For each component, we generate:
- a metaclass. These metaclasses are used when referring to specific components when using the API -
every template parameter
T
expects a metaclass argument. - an
Update
class nested inside the metaclass. This has an optional field for each field in the component (since it represents a diff). - command
Request
andResponse
classes nested inside the metaclass. These have an optional field for each command defined by the component (using the request type and response type of the command respectively); however, only one field can be set at a time. Note that the behaviour of responding to a command request using the response field for a different command is undefined.
Data representation
- Strings are represented as UTF-8 encoded
std::string
members. Make sure to use this same encoding when updating a component. list<T>
fields are represented as aworker::List<T>
of the repeated type. This type is very similar tostd::vector<T>
and has most of the methods you’d expect.map<Key, Value>
fields are represented asworker::Map<Key, Value>
. This type is very similar tostd::unordered_map<Key, Value>
and has most of the methods you’d expect. The biggest difference is it has a well-defined iteration order, which is insertion order.option<T>
fields are represented asworker::Option<T>
. First, check if the option contains a value with!option.empty()
orif (option) { ... }
, then dereference the option to access the contained value. This type is very similar to thestd::optional<T>
type introduced in C++17.
Example
Consider the following simple schema:
package example;
type StatusEffect {
string name = 1;
int32 multiplier = 2;
}
type EntityStatus {
int32 health = 1;
list<StatusEffect> effects = 2;
}
component Status {
id = 12345;
data EntityStatus;
}
Here is the interface that will be generated for this schema (roughly - it has been simplified for clarity):
namespace example {
// The data class for the StatusEffect message.
class StatusEffect {
public:
StatusEffect(const string& name, int32_t multiplier);
const string& name() const;
string& name();
StatusEffect& set_name(const string&);
int32_t multiplier() const;
int32_t& multiplier();
EntityStatus& set_multiplier(int32_t);
};
// The data class for the EntityStatus message.
class EntityStatus {
public:
EntityStatus(int32_t health, const Range<const StatusEffect>& status_effect);
int32_t health() const;
int32_t& health();
EntityStatus& set_health(int32_t);
const List<StatusEffect>& effects() const;
List<StatusEffect>& effects();
EntityStatus& set_effects(const List<StatusEffect>&);
};
// The metaclass for the status component.
struct Status {
using Data = EntityStatus;
// The update class for the status component.
class Update {
const Option<int32_t>& health() const;
Option<int32_t>& health();
Update& set_health(int32_t);
const Option<List<StatusEffect>>& effects() const;
Option<List<StatusEffect>>& effects();
Update& set_effects(const List<StatusEffect>&);
};
};
}
Note that we have data classes EntityStatus
and StatusEffect
corresponding to the two types
defined in the schema, and also a Status
metaclass containing a Status::Update
class for the
status
component. The generated code uses some helper types like Range
which are defined in
<improbable/schema_lib.h>
.
The Status
metaclass can be passed as a template parameter to any templated API function, for
example to send an update for the Status
component. Note that the Status
metaclass is also used
with the worker::Entity
class (which the View
uses to represent entities) to inspect component
data “at rest”.
Here are some ways that these classes can be used with the API:
#include <improbable/worker.h>
#include <schema/example.h>
using namespace worker;
using namespace example;
void Examples(Connection& connection) {
Dispatcher dispatcher;
dispatcher.OnAuthorityChange<Status>([&](const AuthorityChangeOp& op) {
if (op.HasAuthority) {
// We were granted authority over the status component. Send an update.
Status::Update update;
update.set_health(10);
connection.SendComponentUpdate<Status>(op.EntityId, update);
} else {
// Authority was revoked.
}
});
dispatcher.OnComponentUpdate<Status>([&](const ComponentUpdateOp<Status>& op) {
const Status::Update& update = op.Update;
if (update.has_effects()) {
// The `effects` field was updated.
}
});
}
Snapshots
The SDK provides two methods to manipulate snapshots stored in files:
/** Load a snapshot from a file. Returns an error message if an error occured. */
Option<std::string> LoadSnapshot(const std::string& path,
std::unordered_map<EntityId, Entity>& entities_output);
/** Saves a snapshot to a file. Returns an error message if an error occured. */
Option<std::string> SaveSnapshot(const std::string& path,
const std::unordered_map<EntityId, Entity>& entities);
Note that, unlike the rest of the API described in this document, snapshot manipulation does not require a Connection
,
making it possible to develop standalone, offline snapshot manipulation tools. However, we recommend using the build
infrastructure provided by SpatialOS for workers to build your standalone tools.
Here is an example of loading a snapshot, performing some manipulation on it, and saving it back. It uses the types and components defined in the example above.
void AddLowHealthEffectToEntities(const std::string& snapshot_filename) {
// Load a snapshot from a file.
std::unordered_map<worker::EntityId, worker::Entity> entities;
auto load_error_opt = worker::LoadSnapshot(snapshot_filename, entities);
if (load_error_opt) {
std::cerr << "Error loading snapshot: " << *load_error_opt << std::endl;
return;
}
// Add the "LowHealth" effect to all entities that have a Status component and less than 10 health points.
for (const auto& pair : entities) {
auto entity = pair.second;
auto status = entity.Get<Status>();
if (status && status->Health() < 10) {
status->Effects().append({"LowHealth", 100});
}
}
// Save the snapshot back to the file.
auto save_error_opt = worker::SaveSnapshot(snapshot_filename, entities);
if (save_error_opt) {
std::cerr << "Error saving snapshot: " << *save_error_opt << std::endl;
return;
}
}
Currently, the generated code for every component present in the snapshot must be linked into the binary that operates on it. Generated code for components that are present in the snapshot, but that your code doesn’t refer to, may be optimized away by the linker.
This generally is not a problem when writing tools designed to create seed snapshots from which to start a new deployment, since such tools must explicitly create each entity and component in the snapshot.
For migration tools which are intended to modify an existing snapshot, it might be a problem, since components not explicitly mentioned by the code itself might not be recognised. This could trigger error messages reporting these components as unknown. An easy workaround is to add code similar to the following to a program experiencing these errors, to force the generated code to be linked:
worker::Entity entity;
entity.Get<UnreferencedComponent>();
Otherwise, the set of active components can be set explicitly before loading the snapshot using the
worker::SetComponentMetaclasses
function.