RTI Connext C API
Version 5.3.1
|
Information that accompanies each sample that is read
or taken
.
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Data Fields | |
DDS_SampleStateKind | sample_state |
The sample state of the sample. | |
DDS_ViewStateKind | view_state |
The view state of the instance. | |
DDS_InstanceStateKind | instance_state |
The instance state of the instance. | |
struct DDS_Time_t | source_timestamp |
The timestamp when the sample was written by a DataWriter. | |
DDS_InstanceHandle_t | instance_handle |
Identifies locally the corresponding instance. | |
DDS_InstanceHandle_t | publication_handle |
Identifies locally the DataWriter that modified the instance. | |
DDS_Long | disposed_generation_count |
The disposed generation count of the instance at the time of sample reception. | |
DDS_Long | no_writers_generation_count |
The no writers generation count of the instance at the time of sample reception. | |
DDS_Long | sample_rank |
The sample rank of the sample. | |
DDS_Long | generation_rank |
The generation rank of the sample. | |
DDS_Long | absolute_generation_rank |
The absolute generation rank of the sample. | |
DDS_Boolean | valid_data |
Indicates whether the DataSample contains data or else it is only used to communicate a change in the instance_state of the instance. | |
struct DDS_Time_t | reception_timestamp |
<<extension>> The timestamp when the sample was committed by a DataReader. | |
struct DDS_SequenceNumber_t | publication_sequence_number |
<<extension>> The publication sequence number. | |
struct DDS_SequenceNumber_t | reception_sequence_number |
<<extension>> The reception sequence number when sample was committed by a DataReader | |
struct DDS_GUID_t | original_publication_virtual_guid |
<<extension>> The original publication virtual GUID. | |
struct DDS_SequenceNumber_t | original_publication_virtual_sequence_number |
<<extension>> The original publication virtual sequence number. | |
struct DDS_GUID_t | related_original_publication_virtual_guid |
<<extension>> The original publication virtual GUID of a related sample. | |
struct DDS_SequenceNumber_t | related_original_publication_virtual_sequence_number |
<<extension>> The original publication virtual sequence number of a related sample. | |
DDS_SampleFlag | flag |
<<extension>> Flags associated with the sample. | |
struct DDS_GUID_t | source_guid |
<<extension>> The application logical data source associated with the sample. | |
struct DDS_GUID_t | related_source_guid |
<<extension>> The application logical data source that is related to the sample. | |
struct DDS_GUID_t | related_subscription_guid |
<<extension>> The related_reader_guid associated with the sample. | |
struct DDS_GUID_t | topic_query_guid |
<<extension>> The GUID of the DDS_TopicQuery that is related to the sample. | |
Information that accompanies each sample that is read
or taken
.
The DDS_SampleInfo contains information pertaining to the associated Data
instance sample including:
the sample_state
of the Data
value (i.e., if it has already been read or not)
the view_state
of the related instance (i.e., if the instance is new or not)
instance_state
of the related instance (i.e., if the instance is alive or not) instance_state
of the corresponding instance. disposed_generation_count
and no_writers_generation_count
for the related instance at the time the sample was received. These counters indicate the number of times the instance had become ALIVE (with instance_state=
DDS_ALIVE_INSTANCE_STATE) at the time the sample was received. The sample_rank
and generation_rank
of the sample within the returned sequence. These ranks provide a preview of the samples that follow within the sequence returned by the read
or take
operations.
absolute_generation_rank
of the sample within the DDS_DataReader. This rank provides a preview of what is available within the DDS_DataReader. source_timestamp
of the sample. This is the timestamp provided by the DDS_DataWriter at the time the sample was produced. For each instance, RTI Connext internally maintains two counts, the DDS_SampleInfo::disposed_generation_count and DDS_SampleInfo::no_writers_generation_count, relative to each DataReader:
The DDS_SampleInfo::disposed_generation_count and DDS_SampleInfo::no_writers_generation_count available in the DDS_SampleInfo capture a snapshot of the corresponding counters at the time the sample was received.
The DDS_SampleInfo::sample_rank and DDS_SampleInfo::generation_rank available in the DDS_SampleInfo are computed based solely on the actual samples in the ordered collection returned by read or take.
The DDS_SampleInfo::generation_rank is computed using the formula:
generation_rank = (MRSIC.disposed_generation_count + MRSIC.no_writers_generation_count) - (S.disposed_generation_count + S.no_writers_generation_count)
The DDS_SampleInfo::absolute_generation_rank available in the DDS_SampleInfo indicates the difference in "generations" between the sample (S) and the Most Recent Sample of the same instance that the middleware has received (MRS). That is, it counts the number of times the instance transitioned from not-alive to alive in the time from the reception of the S to the time when the read or take was called.
absolute_generation_rank = (MRS.disposed_generation_count + MRS.no_writers_generation_count) - (S.disposed_generation_count + S.no_writers_generation_count)
These counters and ranks allow the application to distinguish samples belonging to different "generations" of the instance. Note that it is possible for an instance to transition from not-alive to alive (and back) several times before the application accesses the data by means of read or take. In this case, the returned collection may contain samples that cross generations (i.e. some samples were received before the instance became not-alive, other after the instance re-appeared again). Using the information in the DDS_SampleInfo, the application can anticipate what other information regarding the same instance appears in the returned collection, as well as in the infrastructure and thus make appropriate decisions.
For example, an application desiring to only consider the most current sample for each instance would only look at samples with sample_rank == 0. Similarly, an application desiring to only consider samples that correspond to the latest generation in the collection will only look at samples with generation_rank == 0. An application desiring only samples pertaining to the latest generation available will ignore samples for which absolute_generation_rank != 0. Other application-defined criteria may also be used.
instance_state
and view_state
of a single instanceDDS_SampleStateKind DDS_SampleInfo::sample_state |
The sample state of the sample.
Indicates whether or not the corresponding data sample has already been read.
DDS_ViewStateKind DDS_SampleInfo::view_state |
The view state of the instance.
Indicates whether the DDS_DataReader has already seen samples for the most-current generation of the related instance.
DDS_InstanceStateKind DDS_SampleInfo::instance_state |
The instance state of the instance.
Indicates whether the instance is currently in existence or, if it has been disposed, the reason why it was disposed.
struct DDS_Time_t DDS_SampleInfo::source_timestamp |
The timestamp when the sample was written by a DataWriter.
DDS_InstanceHandle_t DDS_SampleInfo::instance_handle |
Identifies locally the corresponding instance.
DDS_InstanceHandle_t DDS_SampleInfo::publication_handle |
Identifies locally the DataWriter that modified the instance.
The publication_handle
is the same DDS_InstanceHandle_t that is returned by the operation DDS_DataReader_get_matched_publications and can also be used as a parameter to the operation DDS_DataReader_get_matched_publication_data.
DDS_Long DDS_SampleInfo::disposed_generation_count |
The disposed generation count of the instance at the time of sample reception.
Indicates the number of times the instance had become alive after it was disposed explicitly by a DDS_DataWriter, at the time the sample was received.
DDS_Long DDS_SampleInfo::no_writers_generation_count |
The no writers generation count of the instance at the time of sample reception.
Indicates the number of times the instance had become alive after it was disposed because there were no writers, at the time the sample was received.
DDS_Long DDS_SampleInfo::sample_rank |
The sample rank of the sample.
Indicates the number of samples related to the same instance that follow in the collection returned by read
or take
.
DDS_Long DDS_SampleInfo::generation_rank |
The generation rank of the sample.
Indicates the generation difference (number of times the instance was disposed and become alive again) between the time the sample was received, and the time the most recent sample in the collection related to the same instance was received.
DDS_Long DDS_SampleInfo::absolute_generation_rank |
The absolute generation rank of the sample.
Indicates the generation difference (number of times the instance was disposed and become alive again) between the time the sample was received, and the time the most recent sample (which may not be in the returned collection) related to the same instance was received.
DDS_Boolean DDS_SampleInfo::valid_data |
Indicates whether the DataSample
contains data or else it is only used to communicate a change in the instance_state
of the instance.
Normally each DataSample
contains both a DDS_SampleInfo and some Data. However there are situations where a DataSample
contains only the DDS_SampleInfo and does not have any associated data. This occurs when the RTI Connext notifies the application of a change of state for an instance that was caused by some internal mechanism (such as a timeout) for which there is no associated data. An example of this situation is when the RTI Connext detects that an instance has no writers and changes the corresponding instance_state to DDS_NOT_ALIVE_NO_WRITERS_INSTANCE_STATE.
The application can distinguish whether a particular DataSample
has data by examining the value of the DDS_SampleInfo::valid_data
. If this flag is set to DDS_BOOLEAN_TRUE, then the DataSample
contains valid Data. If the flag is set to DDS_BOOLEAN_FALSE, the DataSample
contains no Data.
To ensure correctness and portability, the valid_data
flag must be examined by the application prior to accessing the Data associated with the DataSample
and if the flag is set to DDS_BOOLEAN_FALSE, the application should not access the Data associated with the DataSample
, that is, the application should access only the DDS_SampleInfo.
struct DDS_Time_t DDS_SampleInfo::reception_timestamp |
<<extension>> The timestamp when the sample was committed by a DataReader.
struct DDS_SequenceNumber_t DDS_SampleInfo::publication_sequence_number |
<<extension>> The publication sequence number.
struct DDS_SequenceNumber_t DDS_SampleInfo::reception_sequence_number |
<<extension>> The reception sequence number when sample was committed by a DataReader
struct DDS_GUID_t DDS_SampleInfo::original_publication_virtual_guid |
<<extension>> The original publication virtual GUID.
If the DDS_PresentationQosPolicy::access_scope of the DDS_Publisher is DDS_GROUP_PRESENTATION_QOS, this field contains the DDS_Publisher virtual GUID that uniquely identifies the DataWriter group.
struct DDS_SequenceNumber_t DDS_SampleInfo::original_publication_virtual_sequence_number |
<<extension>> The original publication virtual sequence number.
If the DDS_PresentationQosPolicy::access_scope of the DDS_Publisher is DDS_GROUP_PRESENTATION_QOS, this field contains the DDS_Publisher virtual sequence number that uniquely identifies a sample within the DataWriter group.
struct DDS_GUID_t DDS_SampleInfo::related_original_publication_virtual_guid |
<<extension>> The original publication virtual GUID of a related sample.
struct DDS_SequenceNumber_t DDS_SampleInfo::related_original_publication_virtual_sequence_number |
<<extension>> The original publication virtual sequence number of a related sample.
DDS_SampleFlag DDS_SampleInfo::flag |
<<extension>> Flags associated with the sample.
The flags can be set by using the field DDS_WriteParams_t::flag when writing a sample using the function FooDataWriter_write_w_params.
struct DDS_GUID_t DDS_SampleInfo::source_guid |
<<extension>> The application logical data source associated with the sample.
The source_guid can be set by using the field DDS_WriteParams_t::source_guid when writing a sample using the function FooDataWriter_write_w_params.
struct DDS_GUID_t DDS_SampleInfo::related_source_guid |
<<extension>> The application logical data source that is related to the sample.
The related_source_guid can be set by using the field DDS_WriteParams_t::related_source_guid when writing a sample using the function FooDataWriter_write_w_params.
struct DDS_GUID_t DDS_SampleInfo::related_subscription_guid |
<<extension>> The related_reader_guid associated with the sample.
The related_reader_guid can be set by using the field DDS_WriteParams_t::related_reader_guid when writing a sample using the function FooDataWriter_write_w_params.
struct DDS_GUID_t DDS_SampleInfo::topic_query_guid |
<<extension>> The GUID of the DDS_TopicQuery that is related to the sample.
This GUID indicates whether a sample is part of the response to a DDS_TopicQuery or a regular ("live") sample: