ResourceLimitsQosPolicy Class Reference
[RESOURCE_LIMITS]

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...

Inheritance diagram for ResourceLimitsQosPolicy:

QosPolicy

List of all members.

Public Attributes

int max_samples
 Represents the maximum samples the middleware can store for any one com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader).
int max_instances
 Represents the maximum number of instances a com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader) can manage.
int max_samples_per_instance
 Represents the maximum number of samples of any one instance a com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader) can manage.
int initial_samples
 <<eXtension>> Represents the initial samples the middleware will store for any one com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader).
int initial_instances
 <<eXtension>> Represents the initial number of instances a com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader) will manage.
int instance_hash_buckets
 <<eXtension>> Number of hash buckets for instances.

Static Public Attributes

static final int LENGTH_UNLIMITED
 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:
com.rti.dds.topic.Topic, com.rti.dds.subscription.DataReader, com.rti.dds.publication.DataWriter
Status:
StatusKind.SAMPLE_REJECTED_STATUS, com.rti.dds.subscription.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 com.rti.dds.infrastructure.DurabilityQosPolicy), this QoS policy determines the actual maximum queue size when the com.rti.dds.infrastructure.HistoryQosPolicy is set to 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 com.rti.dds.publication.DataWriter objects are communicating samples faster than they are ultimately taken by the com.rti.dds.subscription.DataReader objects, the middleware will eventually hit against some of the QoS-imposed resource limits. Note that this may occur when just a single com.rti.dds.subscription.DataReader cannot keep up with its corresponding com.rti.dds.publication.DataWriter. The behavior in this case depends on the setting for the RELIABILITY. If reliability is ReliabilityQosPolicyKind.BEST_EFFORT_RELIABILITY_QOS, then RTI Connext is allowed to drop samples. If the reliability is ReliabilityQosPolicyKind.RELIABLE_RELIABILITY_QOS, RTI Connext will block the com.rti.dds.publication.DataWriter or discard the sample at the com.rti.dds.subscription.DataReader in order not to lose existing samples.

The constant ResourceLimitsQosPolicy.LENGTH_UNLIMITED may be used to indicate the absence of a particular limit. For example setting com.rti.dds.infrastructure.ResourceLimitsQosPolicy.max_samples_per_instance to 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 com.rti.dds.publication.DataWriter may block on a write() call even though the com.rti.dds.infrastructure.HistoryQosPolicy is HistoryQosPolicyKind.KEEP_LAST_HISTORY_QOS. To guarantee the writer does not block for HistoryQosPolicyKind.KEEP_LAST_HISTORY_QOS, make sure the resource limits are set such that:

 max_samples >= max_instances * max_samples_per_instance 

See also:
com.rti.dds.infrastructure.ReliabilityQosPolicy

com.rti.dds.infrastructure.HistoryQosPolicy

Consistency

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

Member Data Documentation

Represents the maximum samples the middleware can store for any one com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader).

Specifies the maximum number of data samples a com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.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 ResourceLimitsQosPolicy.LENGTH_UNLIMITED.

When batching is enabled, the maximum number of data samples a com.rti.dds.publication.DataWriter can manage will also be limited by com.rti.dds.infrastructure.DataWriterResourceLimitsQosPolicy.max_batches.

[default] ResourceLimitsQosPolicy.LENGTH_UNLIMITED

[range] [1, 100 million] or ResourceLimitsQosPolicy.LENGTH_UNLIMITED, >= initial_samples, >= max_samples_per_instance, >= com.rti.dds.infrastructure.DataReaderResourceLimitsQosPolicy.max_samples_per_remote_writer or >= com.rti.dds.infrastructure.RtpsReliableWriterProtocol_t.heartbeats_per_max_samples

For com.rti.dds.publication.DataWriterQos max_samples >= com.rti.dds.infrastructure.DataWriterProtocolQosPolicy.rtps_reliable_writer.heartbeats_per_max_samples if batching is disabled.

Represents the maximum number of instances a com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader) can manage.

[default] ResourceLimitsQosPolicy.LENGTH_UNLIMITED

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

Represents the maximum number of samples of any one instance a com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader) can manage.

For unkeyed types, this value has to be equal to max_samples or ResourceLimitsQosPolicy.LENGTH_UNLIMITED.

[default] ResourceLimitsQosPolicy.LENGTH_UNLIMITED

[range] [1, 100 million] or ResourceLimitsQosPolicy.LENGTH_UNLIMITED, <= max_samples or ResourceLimitsQosPolicy.LENGTH_UNLIMITED, >= com.rti.dds.infrastructure.HistoryQosPolicy.depth

<<eXtension>> Represents the initial samples the middleware will store for any one com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader).

Specifies the initial number of data samples a com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader) will manage across all the instances associated with it.

[default] 32

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

<<eXtension>> Represents the initial number of instances a com.rti.dds.publication.DataWriter (or com.rti.dds.subscription.DataReader) will manage.

[default] 32

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

<<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]


RTI Connext Java API Version 4.5f Copyright © 17 Mar 2012 Real-Time Innovations, Inc