Flow Controllers

<<eXtension>> DDS::FlowController and associated elements More...

Classes
struct	DDS::FlowControllerTokenBucketProperty_t
	DDS::FlowController uses the popular token bucket approach for open loop network flow control. The flow control characteristics are determined by the token bucket properties. More...
class	DDS::FlowControllerProperty_t
	Determines the flow control characteristics of the DDS::FlowController. More...
class	DDS::FlowController
	<<interface>> A flow controller is the object responsible for shaping the network traffic by determining when attached asynchronous DDS::DataWriter instances are allowed to write data. More...

Enumerations
enum	DDS::FlowControllerSchedulingPolicy : UINT32
	Kinds of flow controller scheduling policy. More...

Properties
static System::String^	DDS::FlowController::DEFAULT_FLOW_CONTROLLER_NAME [get]
	[default] Special value of DDS::PublishModeQosPolicy::flow_controller_name that refers to the built-in default flow controller.
static System::String^	DDS::FlowController::FIXED_RATE_FLOW_CONTROLLER_NAME [get]
	Special value of DDS::PublishModeQosPolicy::flow_controller_name that refers to the built-in fixed-rate flow controller.
static System::String^	DDS::FlowController::ON_DEMAND_FLOW_CONTROLLER_NAME [get]
	Special value of DDS::PublishModeQosPolicy::flow_controller_name that refers to the built-in on-demand flow controller.

Detailed Description

<<eXtension>> DDS::FlowController and associated elements

DDS::FlowController provides the network traffic shaping capability to asynchronous DDS::DataWriter instances. For use cases and advantages of publishing asnychronously, please refer to DDS::PublishModeQosPolicy of DDS::DataWriterQos.

See Also

DDS::PublishModeQosPolicy

DDS::DataWriterQos::publish_mode

DDS::AsynchronousPublisherQosPolicy

Enumeration Type Documentation

enum DDS::FlowControllerSchedulingPolicy : UINT32

Kinds of flow controller scheduling policy.

Samples written by an asynchronous DDS::DataWriter are not sent in the context of the DDS::TypedDataWriter::write call. Instead, the middleware puts the samples in a queue for future processing. The DDS::FlowController associated with each asynchronous DataWriter instance determines when the samples are actually sent.

Each DDS::FlowController maintains a separate FIFO queue for each unique destination (remote application). Samples written by asynchronous DDS::DataWriter instances associated with the flow controller, are placed in the queues that correspond to the intended destinations of the sample.

When tokens become available, a flow controller must decide which queue(s) to grant tokens first. This is determined by the flow controller's scheduling policy. Once a queue has been granted tokens, it is serviced by the asynchronous publishing thread. The queued up samples will be coalesced and sent to the corresponding destination. The number of samples sent depends on the data size and the number of tokens granted.

QoS:

DDS::FlowControllerProperty_t

Properties

System:: String^ DDS::FlowController::DEFAULT_FLOW_CONTROLLER_NAME

staticget

[default] Special value of DDS::PublishModeQosPolicy::flow_controller_name that refers to the built-in default flow controller.

RTI Connext provides several built-in DDS::FlowController for use with an asynchronous DDS::DataWriter. The user can choose to use the built-in flow controllers and optionally modify their properties or can create a custom flow controller.

By default, flow control is disabled. That is, the built-in ::DDS::DEFAULT_FLOW_CONTROLLER_NAME flow controller does not apply any flow control. Instead, it allows data to be sent asynchronously as soon as it is written by the DDS::DataWriter.

Essentially, this is equivalent to a user-created DDS::FlowController with the following DDS::FlowControllerProperty_t settings:

- DDS::FlowControllerProperty_t::scheduling_policy = ::DDS::FlowControllerSchedulingPolicy::EDF_FLOW_CONTROLLER_SCHED_POLICY

- DDS::FlowControllerProperty_t::token_bucket max_tokens = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

- DDS::FlowControllerProperty_t::token_bucket tokens_added_per_period = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

- DDS::FlowControllerProperty_t::token_bucket tokens_leaked_per_period = 0

- DDS::FlowControllerProperty_t::token_bucket period = 1 second

- DDS::FlowControllerProperty_t::token_bucket bytes_per_token = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

See Also

DDS::Publisher::create_datawriter

DDS::DomainParticipant::lookup_flowcontroller

DDS::FlowController::set_property

DDS::PublishModeQosPolicy

DDS::AsynchronousPublisherQosPolicy

System:: String^ DDS::FlowController::FIXED_RATE_FLOW_CONTROLLER_NAME

staticget

Special value of DDS::PublishModeQosPolicy::flow_controller_name that refers to the built-in fixed-rate flow controller.

RTI Connext provides several builtin DDS::FlowController for use with an asynchronous DDS::DataWriter. The user can choose to use the built-in flow controllers and optionally modify their properties or can create a custom flow controller.

The built-in ::DDS::FIXED_RATE_FLOW_CONTROLLER_NAME flow controller shapes the network traffic by allowing data to be sent only once every second. Any accumulated samples destined for the same destination are coalesced into as few network packets as possible.

Essentially, this is equivalent to a user-created DDS::FlowController with the following DDS::FlowControllerProperty_t settings:

- DDS::FlowControllerProperty_t::scheduling_policy = ::DDS::FlowControllerSchedulingPolicy::EDF_FLOW_CONTROLLER_SCHED_POLICY

- DDS::FlowControllerProperty_t::token_bucket max_tokens = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

- DDS::FlowControllerProperty_t::token_bucket tokens_added_per_period = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

- DDS::FlowControllerProperty_t::token_bucket tokens_leaked_per_period = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

- DDS::FlowControllerProperty_t::token_bucket period = 1 second

- DDS::FlowControllerProperty_t::token_bucket bytes_per_token = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

See Also

DDS::Publisher::create_datawriter

DDS::DomainParticipant::lookup_flowcontroller

DDS::FlowController::set_property

DDS::PublishModeQosPolicy

DDS::AsynchronousPublisherQosPolicy

System:: String^ DDS::FlowController::ON_DEMAND_FLOW_CONTROLLER_NAME

staticget

Special value of DDS::PublishModeQosPolicy::flow_controller_name that refers to the built-in on-demand flow controller.

RTI Connext provides several builtin DDS::FlowController for use with an asynchronous DDS::DataWriter. The user can choose to use the built-in flow controllers and optionally modify their properties or can create a custom flow controller.

The built-in ::DDS::ON_DEMAND_FLOW_CONTROLLER_NAME allows data to be sent only when the user calls DDS::FlowController::trigger_flow. With each trigger, all accumulated data since the previous trigger is sent (across all DDS::Publisher or DDS::DataWriter instances). In other words, the network traffic shape is fully controlled by the user. Any accumulated samples destined for the same destination are coalesced into as few network packets as possible.

This external trigger source is ideal for users who want to implement some form of closed-loop flow control or who want to only put data on the wire every so many samples (e.g. with the number of samples based on ::DDS::Transport_Property_t::gather_send_buffer_count_max).

Essentially, this is equivalent to a user-created DDS::FlowController with the following DDS::FlowControllerProperty_t settings:

- DDS::FlowControllerProperty_t::scheduling_policy = ::DDS::FlowControllerSchedulingPolicy::EDF_FLOW_CONTROLLER_SCHED_POLICY

- DDS::FlowControllerProperty_t::token_bucket max_tokens = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

- DDS::FlowControllerProperty_t::token_bucket tokens_added_per_period = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

- DDS::FlowControllerProperty_t::token_bucket tokens_leaked_per_period = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

- DDS::FlowControllerProperty_t::token_bucket period = DDS::Duration_t::DURATION_INFINITE

- DDS::FlowControllerProperty_t::token_bucket bytes_per_token = DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

See Also

DDS::Publisher::create_datawriter

DDS::DomainParticipant::lookup_flowcontroller

DDS::FlowController::trigger_flow

DDS::FlowController::set_property

DDS::PublishModeQosPolicy

DDS::AsynchronousPublisherQosPolicy