DDS::ResourceLimitsQosPolicy Struct Reference

Controls the amount of physical memory allocated for DDS entities, if dynamic allocations are allowed, and how they occur. Also controls memory usage among different instance values for keyed topics. More...

#include <managed_infrastructure.h>

Static Public Member Functions
static System::String^	get_resourcelimits_qos_policy_name ()
	Stringified human-readable name for DDS::ResourceLimitsQosPolicy.

Public Attributes
System::Int32	max_samples
	Represents the maximum samples the middleware can store for any one DDS::DataWriter (or DDS::DataReader).
System::Int32	max_instances
	Represents the maximum number of instances a DDS::DataWriter (or DDS::DataReader) can manage.
System::Int32	max_samples_per_instance
	Represents the maximum number of samples of any one instance a DDS::DataWriter (or DDS::DataReader) can manage.
System::Int32	initial_samples
	<<eXtension>> Represents the initial samples the middleware will store for any one DDS::DataWriter (or DDS::DataReader).
System::Int32	initial_instances
	<<eXtension>> Represents the initial number of instances a DDS::DataWriter (or DDS::DataReader) will manage.
System::Int32	instance_hash_buckets
	<<eXtension>> Number of hash buckets for instances.

Properties
static System::Int32	LENGTH_UNLIMITED [get]
	A special value indicating an unlimited quantity.

Detailed Description

Controls the amount of physical memory allocated for DDS entities, if dynamic allocations are allowed, and how they occur. Also controls memory usage among different instance values for keyed topics.

Entity:

DDS::Topic, DDS::DataReader, DDS::DataWriter

Status:

::DDS::StatusKind::SAMPLE_REJECTED_STATUS, DDS::SampleRejectedStatus

Properties:

RxO = NO
Changeable = UNTIL ENABLE

Usage

This policy controls the resources that RTI Connext can use to meet the requirements imposed by the application and other QoS settings.

For the reliability protocol (and DDS::DurabilityQosPolicy), this QoS policy determines the actual maximum queue size when the DDS::HistoryQosPolicy is set to ::DDS::HistoryQosPolicyKind::KEEP_ALL_HISTORY_QOS.

In general, this QoS policy is used to limit the amount of system memory that RTI Connext can allocate. For embedded real-time systems and safety-critical systems, pre-determination of maximum memory usage is often required. In addition, dynamic memory allocation could introduce non-deterministic latencies in time-critical paths.

This QoS policy can be set such that an entity does not dynamically allocate any more memory after its initialization phase.

If DDS::DataWriter objects are communicating samples faster than they are ultimately taken by the DDS::DataReader objects, the middleware will eventually hit against some of the QoS-imposed resource limits. Note that this may occur when just a single DDS::DataReader cannot keep up with its corresponding DDS::DataWriter. The behavior in this case depends on the setting for the RELIABILITY. If reliability is ::DDS::ReliabilityQosPolicyKind::BEST_EFFORT_RELIABILITY_QOS, then RTI Connext is allowed to drop samples. If the reliability is ::DDS::ReliabilityQosPolicyKind::RELIABLE_RELIABILITY_QOS, RTI Connext will block the DDS::DataWriter or discard the sample at the DDS::DataReader in order not to lose existing samples.

The constant DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED may be used to indicate the absence of a particular limit. For example setting DDS::ResourceLimitsQosPolicy::max_samples_per_instance to DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED will cause RTI Connext not to enforce this particular limit.

If these resource limits are not set sufficiently, under certain circumstances the DDS::DataWriter may block on a write() call even though the DDS::HistoryQosPolicy is ::DDS::HistoryQosPolicyKind::KEEP_LAST_HISTORY_QOS. To guarantee the writer does not block for ::DDS::HistoryQosPolicyKind::KEEP_LAST_HISTORY_QOS, make sure the resource limits are set such that:

max_samples >= max_instances * max_samples_per_instance 

See Also

DDS::ReliabilityQosPolicy

DDS::HistoryQosPolicy

Consistency

The setting of DDS::ResourceLimitsQosPolicy::max_samples must be consistent with DDS::ResourceLimitsQosPolicy::max_samples_per_instance. For these two values to be consistent, it must be true that DDS::ResourceLimitsQosPolicy::max_samples >= DDS::ResourceLimitsQosPolicy::max_samples_per_instance. As described above, this limit will not be enforced if DDS::ResourceLimitsQosPolicy::max_samples_per_instance is set to DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED.

The setting of RESOURCE_LIMITS max_samples_per_instance must be consistent with the HISTORY depth. For these two QoS to be consistent, it must be true that depth <= max_samples_per_instance.

See Also

DDS::HistoryQosPolicy

Member Data Documentation

System::Int32 DDS::ResourceLimitsQosPolicy::max_samples

Represents the maximum samples the middleware can store for any one DDS::DataWriter (or DDS::DataReader).

Specifies the maximum number of data samples a DDS::DataWriter (or DDS::DataReader) can manage across all the instances associated with it.

For unkeyed types, this value has to be equal to max_samples_per_instance if max_samples_per_instance is not equal to DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED.

When batching is enabled, the maximum number of data samples a DDS::DataWriter can manage will also be limited by DDS::DataWriterResourceLimitsQosPolicy::max_batches.

[default] DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

[range] [1, 100 million] or DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED, >= initial_samples, >= max_samples_per_instance, >= DDS::DataReaderResourceLimitsQosPolicy::max_samples_per_remote_writer or >= DDS::RtpsReliableWriterProtocol_t::heartbeats_per_max_samples

For DDS::DataWriterQos max_samples >= DDS::RtpsReliableWriterProtocol_t::heartbeats_per_max_samples in DDS::DataWriterProtocolQosPolicy::rtps_reliable_writer if batching is disabled.

System::Int32 DDS::ResourceLimitsQosPolicy::max_instances

Represents the maximum number of instances a DDS::DataWriter (or DDS::DataReader) can manage.

[default] DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

[range] [1, 1 million] or DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED, >= initial_instances

System::Int32 DDS::ResourceLimitsQosPolicy::max_samples_per_instance

Represents the maximum number of samples of any one instance a DDS::DataWriter (or DDS::DataReader) can manage.

While an unkeyed type is logically considered as a single instance, for unkeyed types this value has to be equal to max_samples or DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED.

[default] DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED

[range] [1, 100 million] or DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED, <= max_samples or DDS::ResourceLimitsQosPolicy::LENGTH_UNLIMITED, >= DDS::HistoryQosPolicy::depth

System::Int32 DDS::ResourceLimitsQosPolicy::initial_samples

<<eXtension>> Represents the initial samples the middleware will store for any one DDS::DataWriter (or DDS::DataReader).

Specifies the initial number of data samples a DDS::DataWriter (or DDS::DataReader) will manage across all the instances associated with it.

[default] 32

[range] [1,100 million], <= max_samples

System::Int32 DDS::ResourceLimitsQosPolicy::initial_instances

<<eXtension>> Represents the initial number of instances a DDS::DataWriter (or DDS::DataReader) will manage.

[default] 32

[range] [1,1 million], <= max_instances

System::Int32 DDS::ResourceLimitsQosPolicy::instance_hash_buckets

<<eXtension>> Number of hash buckets for instances.

The instance hash table facilitates instance lookup. A higher number of buckets decreases instance lookup time but increases the memory usage.

[default] 1 [range] [1,1 million]