Declares the interface required to support a user data type-specific data reader. More...

#include <dds_cpp_data.hxx>

Inherits DDSDataReader_impl.

Public Member Functions
DDS_ReturnCode_t	return_loan (FooSeq &received_data, DDS_SampleInfoSeq &info_seq)
	Indicates to the DDSDataReader that the application is done accessing the collection of `received_data` and `info_seq` obtained by some earlier invocation of read or take on the DDSDataReader.
DDS_ReturnCode_t	read_next_sample (Foo &received_data, DDS_SampleInfo &sample_info)
	Copies the next not-previously-accessed data value from the DDSDataReader.
DDS_ReturnCode_t	take_next_sample (Foo &received_data, DDS_SampleInfo &sample_info)
	Copies the next not-previously-accessed data value from the DDSDataReader.
DDS_ReturnCode_t	read (FooSeq &received_data, DDS_SampleInfoSeq &info_seq, DDS_Long max_samples, DDS_SampleStateMask sample_states, DDS_ViewStateMask view_states, DDS_InstanceStateMask instance_states)
	Access a collection of data samples from the DDSDataReader.
DDS_ReturnCode_t	take (FooSeq &received_data, DDS_SampleInfoSeq &info_seq, DDS_Long max_samples, DDS_SampleStateMask sample_states, DDS_ViewStateMask view_states, DDS_InstanceStateMask instance_states)
	Access a collection of data-samples from the DDSDataReader.
DDS_ReturnCode_t	read_instance (FooSeq &received_data, DDS_SampleInfoSeq &info_seq, DDS_Long max_samples, const DDS_InstanceHandle_t &a_handle, DDS_SampleStateMask sample_states, DDS_ViewStateMask view_states, DDS_InstanceStateMask instance_states)
	Access a collection of data samples from the DDSDataReader.
DDS_ReturnCode_t	take_instance (FooSeq &received_data, DDS_SampleInfoSeq &info_seq, DDS_Long max_samples, const DDS_InstanceHandle_t &a_handle, DDS_SampleStateMask sample_states, DDS_ViewStateMask view_states, DDS_InstanceStateMask instance_states)
	Access a collection of data samples from the DDSDataReader.

Static Public Member Functions
static FooDataReader *	narrow (DDSDataReader *reader)
	Narrow the given DDSDataReader pointer to a FooDataReader pointer.

Detailed Description

Declares the interface required to support a user data type-specific data reader.

Member Function Documentation

static FooDataReader* FooDataReader::narrow ( DDSDataReader * reader )

static

Narrow the given DDSDataReader pointer to a FooDataReader pointer.

DDS_ReturnCode_t FooDataReader::return_loan	(	FooSeq &	received_data,
		DDS_SampleInfoSeq &	info_seq
	)

Indicates to the DDSDataReader that the application is done accessing the collection of received_data and info_seq obtained by some earlier invocation of read or take on the DDSDataReader.

This operation indicates to the DDSDataReader that the application is done accessing the collection of received_data and info_seq obtained by some earlier invocation of read or take on the DDSDataReader.

The received_data and info_seq must belong to a single related "pair"; that is, they should correspond to a pair returned from a single call to read or take. The received_data and info_seq must also have been obtained from the same DDSDataReader to which they are returned. If either of these conditions is not met, the operation will fail with DDS_RETCODE_PRECONDITION_NOT_MET.

The operation FooDataReader::return_loan allows implementations of the read and take operations to "loan" buffers from the DDSDataReader to the application and in this manner provide "zerocopy" access to the data. During the loan, the DDSDataReader will guarantee that the data and sample-information are not modified.

It is not necessary for an application to return the loans immediately after the read or take calls. However, as these buffers correspond to internal resources inside the DDSDataReader, the application should not retain them indefinitely.

The use of FooDataReader::return_loan is only necessary if the read or take calls "loaned" buffers to the application. This only occurs if the received_data and info_Seq collections had max_len=0 at the time read or take was called.

The application may also examine the "owns" property of the collection to determine where there is an outstanding loan. However, calling FooDataReader::return_loan on a collection that does not have a loan is safe and has no side effects.

If the collections had a loan, upon completion of FooDataReader::return_loan, the collections will have max_len=0.

Similar to read, this operation must be provided on the specialized class that is generated for the particular application data-type that is being taken.

Parameters:

received_data <<in>> user data type-specific FooSeq object where the received data samples was obtained from earlier invocation of read or take on the DDSDataReader.

Parameters:

info_seq <<in>> a DDS_SampleInfoSeq object where the received sample info was obtained from earlier invocation of read or take on the DDSDataReader.

Returns:: One of the Standard Return Codes, DDS_RETCODE_PRECONDITION_NOT_MET or DDS_RETCODE_NOT_ENABLED.

DDS_ReturnCode_t FooDataReader::read_next_sample	(	Foo &	received_data,
		DDS_SampleInfo &	sample_info
	)

Copies the next not-previously-accessed data value from the DDSDataReader.

This operation copies the next not-previously-accessed data value from the DDSDataReader. This operation also copies the corresponding DDS_SampleInfo. The implied order among the samples stored in the DDSDataReader is the same as for the FooDataReader::read operation.

The FooDataReader::read_next_sample operation is semantically equivalent to the FooDataReader::read operation, where the input data sequences has max_len=1, the sample_states=NOT_READ, the view_states=ANY_VIEW_STATE, and the instance_states=ANY_INSTANCE_STATE.

The FooDataReader::read_next_sample operation provides a simplified API to 'read' samples, avoiding the need for the application to manage sequences and specify states.

If there is no unread data in the DDSDataReader, the operation will fail with DDS_RETCODE_NO_DATA and nothing is copied.

Parameters:

received_data	<<inout>> user data type-specific Foo object where the next received data sample will be returned. The received_data must have been fully allocated. Otherwise, this operation may fail.
sample_info	<<inout>> a DDS_SampleInfo object where the next received sample info will be returned.

Returns:: One of the Standard Return Codes, DDS_RETCODE_NO_DATA or DDS_RETCODE_NOT_ENABLED.

See also:: FooDataReader::read

DDS_ReturnCode_t FooDataReader::take_next_sample	(	Foo &	received_data,
		DDS_SampleInfo &	sample_info
	)

Copies the next not-previously-accessed data value from the DDSDataReader.

This operation copies the next not-previously-accessed data value from the DDSDataReader and 'removes' it from the DDSDataReader so that it is no longer accessible. This operation also copies the corresponding DDS_SampleInfo. This operation is analogous to the FooDataReader::read_next_sample except for the fact that the sample is removed from the DDSDataReader.

The FooDataReader::take_next_sample operation is semantically equivalent to the FooDataReader::take operation, where the input data sequences has max_len=1, the sample_states=NOT_READ, the view_states=ANY_VIEW_STATE, and the instance_states=ANY_INSTANCE_STATE.

The FooDataReader::read_next_sample operation provides a simplified API to 'take' samples, avoiding the need for the application to manage sequences and specify states.

If there is no unread data in the DDSDataReader, the operation will fail with DDS_RETCODE_NO_DATA and nothing is copied.

Parameters:

received_data	<<inout>> user data type-specific Foo object where the next received data sample will be returned. The received_data must have been fully allocated. Otherwise, this operation may fail.
sample_info	<<inout>> a DDS_SampleInfo object where the next received sample info will be returned.

Returns:: One of the Standard Return Codes, DDS_RETCODE_NO_DATA or DDS_RETCODE_NOT_ENABLED.

See also:: FooDataReader::take

DDS_ReturnCode_t FooDataReader::read	(	FooSeq &	received_data,
		DDS_SampleInfoSeq &	info_seq,
		DDS_Long	max_samples,
		DDS_SampleStateMask	sample_states,
		DDS_ViewStateMask	view_states,
		DDS_InstanceStateMask	instance_states
	)

Access a collection of data samples from the DDSDataReader.

This operation offers the same functionality and API as FooDataReader::take except that the samples returned remain in the DDSDataReader such that they can be retrieved again by means of a read or take operation.

Please refer to the documentation of FooDataReader::take() for details on the number of samples returned within the received_data and info_seq as well as the order in which the samples appear in these sequences.

The act of reading a sample changes its sample_state to DDS_READ_SAMPLE_STATE. If the sample belongs to the most recent generation of the instance, it will also set the view_state of the instance to be DDS_NOT_NEW_VIEW_STATE. It will not affect the instance_state of the instance.

Important: If the samples "returned" by this method are loaned from RTI Connext DDS Micro (see FooDataReader::take for more information on memory loaning), it is important that their contents not be changed. Because the memory in which the data is stored belongs to the middleware, any modifications made to the data will be seen the next time the same samples are read or taken; the samples will no longer reflect the state that was received from the network.

Parameters:

received_data	<<inout>> User data type-specific FooSeq object where the received data samples will be returned.
info_seq	<<inout>> A DDS_SampleInfoSeq object where the received sample info will be returned.
max_samples	<<in>> The maximum number of samples to be returned. If the special value DDS_LENGTH_UNLIMITED is provided, as many samples will be returned as are available.
sample_states	<<in>> Data samples matching one of these `sample_states` are returned.
view_states	<<in>> Data samples matching one of these `view_state` are returned.
instance_states	<<in>> Data samples matching ones of these `instance_state` are returned.

Returns:: One of the Standard Return Codes, DDS_RETCODE_PRECONDITION_NOT_MET, DDS_RETCODE_NO_DATA or DDS_RETCODE_NOT_ENABLED.

See also:: FooDataReader::take,; DDS_LENGTH_UNLIMITED

DDS_ReturnCode_t FooDataReader::take	(	FooSeq &	received_data,
		DDS_SampleInfoSeq &	info_seq,
		DDS_Long	max_samples,
		DDS_SampleStateMask	sample_states,
		DDS_ViewStateMask	view_states,
		DDS_InstanceStateMask	instance_states
	)

Access a collection of data-samples from the DDSDataReader.

The operation will return the list of samples received by the DDSDataReader since the last FooDataReader::take operation that match the specified DDS_SampleStateMask, DDS_ViewStateMask and DDS_InstanceStateMask.

In the case where the DDS_HistoryQosPolicy::kind is DDS_KEEP_LAST_HISTORY_QOS (currently the only supported configuration), the call will return at most DDS_HistoryQosPolicy::depth samples per instance.

The maximum number of samples returned is limited by DDS_ResourceLimitsQosPolicy::max_samples

For multiple instances, the number of samples returned is additionally limited by the product (DDS_ResourceLimitsQosPolicy::max_samples_per_instance * DDS_ResourceLimitsQosPolicy::max_instances )

If the read or take succeeds and the number of samples returned has been limited (by means of a maximum limit, as listed above, or insufficient DDS_SampleInfo resources), the call will complete successfully and provide those samples the reader is able to return. The user may need to make additional calls, or return outstanding loaned buffers in the case of insuffificient resources, in order to access remaining samples.

Note that in the case where the DDSTopic associated with the DDSDataReader is bound to a data-type that has no key definition, then there will be at most one instance in the DDSDataReader. So the per-sample limits will apply.

The act of taking a sample removes it from RTI Connext DDS Micro so it cannot be read or taken again. If the sample belongs to the most recent generation of the instance, it will also set the view_state of the sample's instance to DDS_NOT_NEW_VIEW_STATE. It will not affect the instance_state of the sample's instance.

After FooDataReader::take completes, received_data and info_seq will be of the same length and contain the received data.

If the sequences are empty (maximum size equal 0) when the FooDataReader::take is called, the samples returned in the received_data and the corresponding info_seq are 'loaned' to the application from buffers provided by the DDSDataReader. The application can use them as desired and has guaranteed exclusive access to them.

Once the application completes its use of the samples it must 'return the loan' to the DDSDataReader by calling the FooDataReader::return_loan operation.

Note: While you must call FooDataReader::return_loan at some point, you do not have to do so before the next FooDataReader::take call. However, failure to return the loan will eventually deplete the DDSDataReader of the buffers it needs to receive new samples and eventually samples will start to be lost. The total number of buffers available to the DDSDataReader is specified by the DDS_ResourceLimitsQosPolicy.

If the sequences are not empty (maximum size not equal 0) when the FooDataReader::take is called, samples are copied to received_data and info_seq. The application will not need to call FooDataReader::return_loan.

The samples returned to the caller is a list where samples belonging to the same data instance are consecutive (i.e. instance access scope).

Samples belonging to the same instance will appear in the relative order in which there were received (i.e. reception timestamp destination order, where earlier samples are ahead of later samples).

If the DDSDataReader has no samples that meet the constraints, the method will fail with DDS_RETCODE_NO_DATA.

In addition to the collection of samples, the read and take operations also use a collection of DDS_SampleInfo structures.

SEQUENCES USAGE IN TAKE AND READ

The initial (input) properties of the received_data and info_seq collections will determine the precise behavior of the read or take operation. For the purposes of this description, the collections are modeled as having these properties:

whether the collection container owns the memory of the elements within (owns, see FooSeq::has_ownership)
the current-length (len, see FooSeq::length())
the maximum length (max_len, see FooSeq::maximum())

The initial values of the owns, len and max_len properties for the received_data and info_seq collections govern the behavior of the read and take operations as specified by the following rules:

The values of owns, len and max_len properties for the two collections must be identical. Otherwise read/take will fail with DDS_RETCODE_PRECONDITION_NOT_MET.
On successful output, the values of owns, len and max_len will be the same for both collections.
If the initial max_len==0, then the received_data and info_seq collections will be filled with elements that are loaned by the DDSDataReader. On output, owns will be FALSE, len will be set to the number of values returned, and max_len will be set to a value verifying max_len >= len. The use of this variant allows for zero-copy access to the data and the application will need to return the loan to the DDSDataWriter using FooDataReader::return_loan.
If the initial max_len>0 and owns==FALSE, then the read or take operation will fail with DDS_RETCODE_PRECONDITION_NOT_MET. This avoids the potential hard-to-detect memory leaks caused by an application forgetting to return the loan.
If initial max_len>0 and owns==TRUE, then the read or take operation will copy the received_data values and DDS_SampleInfo values into the elements already inside the collections. On output, owns will be TRUE, len will be set to the number of values copied and max_len will remain unchanged. The use of this variant forces a copy but the application can control where the copy is placed and the application will not need to return the loan. The number of samples copied depends on the relative values of max_len and max_samples:
- If max_samples == LENGTH_UNLIMITED, then at most max_len values will be copied. The use of this variant lets the application limit the number of samples returned to what the sequence can accommodate.
- If max_samples <= max_len, then at most max_samples values will be copied. The use of this variant lets the application limit the number of samples returned to fewer that what the sequence can accommodate.
- If max_samples > max_len, then the read or take operation will fail with DDS_RETCODE_PRECONDITION_NOT_MET. This avoids the potential confusion where the application expects to be able to access up to max_samples, but that number can never be returned, even if they are available in the DDSDataReader, because the output sequence cannot accommodate them.

As described above, upon completion, the received_data and info_seq collections may contain elements loaned from the DDSDataReader. If this is the case, the application will need to use FooDataReader::return_loan to return the loan once it is no longer using the received_data in the collection. When FooDataReader::return_loan completes, the collection will have owns=FALSE and max_len=0. The application can determine whether it is necessary to return the loan or not based on how the state of the collections when the read/take operation was called or by accessing the owns property. However, in many cases it may be simpler to always call FooDataReader::return_loan, as this operation is harmless (i.e., it leaves all elements unchanged) if the collection does not have a loan.

To avoid potential memory leaks, the implementation of the Foo and DDS_SampleInfo collections should disallow changing the length of a collection for which owns==FALSE. Furthermore, deleting a collection for which owns==FALSE should be considered an error.

On output, the collection of Foo values and the collection of DDS_SampleInfo structures are of the same length and are in a one-to-one correspondence. Each DDS_SampleInfo provides information, such as the source_timestamp, the sample_state, view_state, and instance_state, etc., about the corresponding sample.

Some elements in the returned collection may not have valid data. If the instance_state in the DDS_SampleInfo is DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE or DDS_NOT_ALIVE_NO_WRITERS_INSTANCE_STATE, then the last sample for that instance in the collection (that is, the one whose DDS_SampleInfo has sample_rank==0) does not contain valid data.

Samples that contain no data do not count towards the limits imposed by the DDS_ResourceLimitsQosPolicy. The act of reading/taking a sample sets its sample_state to DDS_READ_SAMPLE_STATE.

If the sample belongs to the most recent generation of the instance, it will also set the view_state of the instance to DDS_NOT_NEW_VIEW_STATE. It will not affect the instance_state of the instance.

This operation must be provided on the specialized class that is generated for the particular application data-type that is being read (Foo). If the DDSDataReader has no samples that meet the constraints, the operations fails with DDS_RETCODE_NO_DATA.

Parameters:

received_data <<inout>> User data type-specific FooSeq object where the received data samples will be returned.

Parameters:

info_seq	<<inout>> A DDS_SampleInfoSeq object where the received sample info will be returned.
max_samples	<<in>> The maximum number of samples to be returned. If the special value DDS_LENGTH_UNLIMITED is provided, as many samples will be returned as are available.
sample_states	<<in>> Data samples matching one of these `sample_states` are returned.
view_states	<<in>> Data samples matching one of these `view_state` are returned.
instance_states	<<in>> Data samples matching one of these `instance_state` are returned.

Returns:: One of the Standard Return Codes, DDS_RETCODE_PRECONDITION_NOT_MET, DDS_RETCODE_NO_DATA or DDS_RETCODE_NOT_ENABLED.

See also:: FooDataReader::read; DDS_LENGTH_UNLIMITED

DDS_ReturnCode_t FooDataReader::read_instance	(	FooSeq &	received_data,
		DDS_SampleInfoSeq &	info_seq,
		DDS_Long	max_samples,
		const DDS_InstanceHandle_t &	a_handle,
		DDS_SampleStateMask	sample_states,
		DDS_ViewStateMask	view_states,
		DDS_InstanceStateMask	instance_states
	)

Access a collection of data samples from the DDSDataReader.

This operation accesses a collection of data values from the DDSDataReader. The behavior is identical to FooDataReader::read, except that all samples returned belong to the single specified instance whose handle is a_handle.

Upon successful completion, the data collection will contain samples all belonging to the same instance. The corresponding DDS_SampleInfo verifies DDS_SampleInfo::instance_handle == a_handle.

The FooDataReader::read_instance operation is semantically equivalent to the FooDataReader::read operation, except in building the collection, the DDSDataReader will check that the sample belongs to the specified instance and otherwise it will not place the sample in the returned collection.

The behavior of the FooDataReader::read_instance operation follows the same rules as the FooDataReader::read operation regarding the pre-conditions and post-conditions for the received_data and sample_info. Similar to the FooDataReader::read, the FooDataReader::read_instance operation may 'loan' elements to the output collections, which must then be returned by means of FooDataReader::return_loan.

Similar to the FooDataReader::read, this operation must be provided on the specialized class that is generated for the particular application data-type that is being taken.

If the DDSDataReader has no samples that meet the constraints, the method will fail with DDS_RETCODE_NO_DATA.

This operation may fail with DDS_RETCODE_BAD_PARAMETER if the DDS_InstanceHandle_t a_handle does not correspond to an existing data-object known to the DDSDataReader.

Parameters:

received_data	<<inout>> user data type-specific FooSeq object where the received data samples will be returned.
info_seq	<<inout>> a DDS_SampleInfoSeq object where the received sample info will be returned.
max_samples	<<in>> The maximum number of samples to be returned. If the special value DDS_LENGTH_UNLIMITED is provided, as many samples will be returned as are available.
a_handle	<<in>> The specified instance to return samples for. The method will fail with DDS_RETCODE_BAD_PARAMETER if the `handle` does not correspond to an existing data-object known to the DDSDataReader.
sample_states	<<in>> data samples matching ones of these `sample_states` are returned
view_states	<<in>> data samples matching ones of these `view_state` are returned
instance_states	<<in>> data samples matching ones of these `instance_state` are returned

Returns:: One of the Standard Return Codes, DDS_RETCODE_PRECONDITION_NOT_MET, DDS_RETCODE_NO_DATA or DDS_RETCODE_NOT_ENABLED.

See also:: FooDataReader::read; DDS_LENGTH_UNLIMITED

DDS_ReturnCode_t FooDataReader::take_instance	(	FooSeq &	received_data,
		DDS_SampleInfoSeq &	info_seq,
		DDS_Long	max_samples,
		const DDS_InstanceHandle_t &	a_handle,
		DDS_SampleStateMask	sample_states,
		DDS_ViewStateMask	view_states,
		DDS_InstanceStateMask	instance_states
	)

Access a collection of data samples from the DDSDataReader.

This operation accesses a collection of data values from the DDSDataReader. The behavior is identical to FooDataReader::take, except for that all samples returned belong to the single specified instance whose handle is a_handle.

The semantics are the same for the FooDataReader::take operation, except in building the collection, the DDSDataReader will check that the sample belongs to the specified instance, and otherwise it will not place the sample in the returned collection.

The behavior of the FooDataReader::take_instance operation follows the same rules as the FooDataReader::read operation regarding the pre-conditions and post-conditions for the received_data and sample_info. Similar to the FooDataReader::read, the FooDataReader::take_instance operation may 'loan' elements to the output collections, which must then be returned by means of FooDataReader::return_loan.

Similar to the FooDataReader::read, this operation must be provided on the specialized class that is generated for the particular application data-type that is being taken.

If the DDSDataReader has no samples that meet the constraints, the method fails with DDS_RETCODE_NO_DATA.

This operation may fail with DDS_RETCODE_BAD_PARAMETER if the DDS_InstanceHandle_t a_handle does not correspond to an existing data-object known to the DDSDataReader.

Parameters:

received_data	<<inout>> user data type-specific FooSeq object where the received data samples will be returned.
info_seq	<<inout>> a DDS_SampleInfoSeq object where the received sample info will be returned.
max_samples	<<in>> The maximum number of samples to be returned. If the special value DDS_LENGTH_UNLIMITED is provided, as many samples will be returned as are available.
a_handle	<<in>> The specified instance to return samples for. The method will fail with DDS_RETCODE_BAD_PARAMETER if the `handle` does not correspond to an existing data-object known to the DDSDataReader.
sample_states	<<in>> data samples matching ones of these `sample_states` are returned
view_states	<<in>> data samples matching ones of these `view_state` are returned
instance_states	<<in>> data samples matching ones of these `instance_state` are returned

Returns:: One of the Standard Return Codes, DDS_RETCODE_PRECONDITION_NOT_MET, DDS_RETCODE_NO_DATA or DDS_RETCODE_NOT_ENABLED.

See also:: FooDataReader::take; DDS_LENGTH_UNLIMITED

Public Member Functions

Static Public Member Functions

Detailed Description

Member Function Documentation

SEQUENCES USAGE IN TAKE AND READ