20.1.3.1. DataWriter¶

class DataWriter : public eprosima::fastdds::dds::DomainEntity ¶

Class DataWriter, contains the actual implementation of the behaviour of the DataWriter.

Public Types

enum class LoanInitializationKind¶

How to initialize samples loaned with loan_sample

Values:

enumerator NO_LOAN_INITIALIZATION¶

Do not perform initialization of sample.

This is the default initialization scheme of loaned samples. It is the fastest scheme, but implies the user should take care of writing every field on the data type before calling write on the loaned sample.

enumerator ZERO_LOAN_INITIALIZATION¶

Initialize all memory with zero-valued bytes.

The contents of the loaned sample will be zero-initialized upon return of loan_sample.

enumerator CONSTRUCTED_LOAN_INITIALIZATION¶

Use in-place constructor initialization.

This will call the constructor of the data type over the memory space being returned by loan_sample.

Public Functions

virtual ReturnCode_t enable() override¶

This operation enables the DataWriter.

Returns:: RETCODE_OK is successfully enabled. RETCODE_PRECONDITION_NOT_MET if the Publisher creating this DataWriter is not enabled.

ReturnCode_t write(const void *const data)¶

Write data to the topic.

Parameters:: data – Pointer to the data
Returns:: RETCODE_OK if the data is correctly sent or a ReturnCode related to the specific error otherwise.

ReturnCode_t write(const void *const data, fastdds::rtps::WriteParams &params)¶

Write data with params to the topic.

Parameters:

data – Pointer to the data
params – Extra write parameters.

Returns:

RETCODE_OK if the data is correctly sent or a ReturnCode related to the specific error otherwise.

ReturnCode_t write(const void *const data, const InstanceHandle_t &handle)¶

Write data with handle.

The special value HANDLE_NIL can be used for the parameter handle.This indicates that the identity of the instance should be automatically deduced from the instance_data (by means of the key).

Parameters:

data – Pointer to the data
handle – InstanceHandle_t.

Returns:

RETCODE_PRECONDITION_NOT_MET if the handle introduced does not match with the one associated to the data, RETCODE_OK if the data is correctly sent and RETCODE_ERROR otherwise.

ReturnCode_t write_w_timestamp(const void *const data, const InstanceHandle_t &handle, const fastdds::dds::Time_t &timestamp)¶

This operation performs the same function as write except that it also provides the value for the source_timestamp that is made available to DataReader objects by means of the eprosima::fastdds::dds::SampleInfo::source_timestamp attribute “source_timestamp” inside the SampleInfo. The constraints on the values of the handle parameter and the corresponding error behavior are the same specified for the write operation. This operation may block and return RETCODE_TIMEOUT under the same circumstances described for the write operation. This operation may return RETCODE_OUT_OF_RESOURCES, RETCODE_PRECONDITION_NOT_MET or RETCODE_BAD_PARAMETER under the same circumstances described for the write operation.

Parameters:

data – Pointer to the data
handle – InstanceHandle_t
timestamp – Time_t used to set the source_timestamp.

Returns:

Any of the standard return codes.

InstanceHandle_t register_instance(const void *const instance)¶

Informs that the application will be modifying a particular instance.

It gives an opportunity to the middleware to pre-configure itself to improve performance.

Parameters:: instance – [in] Sample used to get the instance’s key.
Returns:: Handle containing the instance’s key. This handle could be used in successive write or dispose operations. In case of error, HANDLE_NIL will be returned.

InstanceHandle_t register_instance_w_timestamp(const void *const instance, const fastdds::dds::Time_t &timestamp)¶

This operation performs the same function as register_instance and can be used instead of register_instance in the cases where the application desires to specify the value for the source_timestamp. The source_timestamp potentially affects the relative order in which readers observe events from multiple writers. See the QoS policy DESTINATION_ORDER.

This operation may block and return RETCODE_TIMEOUT under the same circumstances described for the write operation.

This operation may return RETCODE_OUT_OF_RESOURCES under the same circumstances described for the write operation.

Parameters:

instance – Sample used to get the instance’s key.
timestamp – Time_t used to set the source_timestamp.

Returns:

Handle containing the instance’s key.

ReturnCode_t unregister_instance(const void *const instance, const InstanceHandle_t &handle)¶

This operation reverses the action of register_instance.

It should only be called on an instance that is currently registered. Informs the middleware that the DataWriter is not intending to modify any more of that data instance. Also indicates that the middleware can locally remove all information regarding that instance.

Parameters:

instance – [in] Sample used to deduce instance’s key in case of handle parameter is HANDLE_NIL.
handle – [in] Instance’s key to be unregistered.

Returns:

Returns the operation’s result. If the operation finishes successfully, RETCODE_OK is returned.

ReturnCode_t unregister_instance_w_timestamp(const void *const instance, const InstanceHandle_t &handle, const fastdds::dds::Time_t &timestamp)¶

This operation performs the same function as unregister_instance and can be used instead of unregister_instance in the cases where the application desires to specify the value for the source_timestamp. The source_timestamp potentially affects the relative order in which readers observe events from multiple writers. See the QoS policy DESTINATION_ORDER.

The constraints on the values of the handle parameter and the corresponding error behavior are the same specified for the unregister_instance operation.

This operation may block and return RETCODE_TIMEOUT under the same circumstances described for the write operation

Parameters:

instance – Sample used to deduce instance’s key in case of handle parameter is HANDLE_NIL.
handle – Instance’s key to be unregistered.
timestamp – Time_t used to set the source_timestamp.

Returns:

Handle containing the instance’s key.

ReturnCode_t get_key_value(void *key_holder, const InstanceHandle_t &handle)¶

This operation can be used to retrieve the instance key that corresponds to an instance_handle. The operation will only fill the fields that form the key inside the key_holder instance.

This operation may return BAD_PARAMETER if the InstanceHandle_t handle does not correspond to an existing data-object known to the DataWriter. If the implementation is not able to check invalid handles then the result in this situation is unspecified.

Parameters:

key_holder – [inout] Sample where the key fields will be returned.
handle – [in] Handle to the instance to retrieve the key values from.

Returns:

Any of the standard return codes.

InstanceHandle_t lookup_instance(const void *const instance) const¶

NOT YET IMPLEMENTED

Takes as a parameter an instance and returns a handle that can be used in subsequent operations that accept an instance handle as an argument. The instance parameter is only used for the purpose of examining the fields that define the key.

Parameters:: instance – [in] Data pointer to the sample
Returns:: handle of the given instance

const fastdds::rtps::GUID_t &guid() const¶

Returns the DataWriter’s GUID

Returns:: Reference to the DataWriter GUID

InstanceHandle_t get_instance_handle() const¶

Returns the DataWriter’s InstanceHandle

Returns:: Copy of the DataWriter InstanceHandle

TypeSupport get_type() const¶

Get data type associated to the DataWriter

Returns:: Copy of the TypeSupport

ReturnCode_t wait_for_acknowledgments(const fastdds::dds::Duration_t &max_wait)¶

Waits the current thread until all writers have received their acknowledgments.

Parameters:: max_wait – Maximum blocking time for this operation
Returns:: RETCODE_OK if the DataWriter receive the acknowledgments before the time expires and RETCODE_ERROR otherwise

ReturnCode_t get_offered_deadline_missed_status(OfferedDeadlineMissedStatus &status)¶

Returns the offered deadline missed status.

Parameters:: status – [out] Deadline missed status struct
Returns:: RETCODE_OK

ReturnCode_t get_offered_incompatible_qos_status(OfferedIncompatibleQosStatus &status)¶

Returns the offered incompatible qos status.

Parameters:: status – [out] Offered incompatible qos status struct
Returns:: RETCODE_OK

ReturnCode_t get_publication_matched_status(PublicationMatchedStatus &status) const¶

Returns the publication matched status.

Parameters:: status – [out] publication matched status struct
Returns:: RETCODE_OK

ReturnCode_t set_qos(const DataWriterQos &qos)¶

Establishes the DataWriterQos for this DataWriter.

Parameters:: qos – DataWriterQos to be set
Returns:: RETCODE_IMMUTABLE_POLICY if any of the Qos cannot be changed, RETCODE_INCONSISTENT_POLICY if the Qos is not self consistent and RETCODE_OK if the qos is changed correctly.

const DataWriterQos &get_qos() const¶

Retrieves the DataWriterQos for this DataWriter.

Returns:: Reference to the current DataWriterQos

ReturnCode_t get_qos(DataWriterQos &qos) const¶

Fills the DataWriterQos with the values of this DataWriter.

Parameters:: qos – DataWriterQos object where the qos is returned.
Returns:: RETCODE_OK

Topic *get_topic() const¶

Retrieves the topic for this DataWriter.

Returns:: Pointer to the associated Topic

const DataWriterListener *get_listener() const¶

Retrieves the listener for this DataWriter.

Returns:: Pointer to the DataWriterListener

ReturnCode_t set_listener(DataWriterListener *listener)¶

Modifies the DataWriterListener, sets the mask to StatusMask::all()

Parameters:: listener – new value for the DataWriterListener
Returns:: RETCODE_OK

ReturnCode_t set_listener(DataWriterListener *listener, const StatusMask &mask)¶

Modifies the DataWriterListener.

Parameters:

listener – new value for the DataWriterListener
mask – StatusMask that holds statuses the listener responds to (default: all).

Returns:

RETCODE_OK

ReturnCode_t dispose(const void *const data, const InstanceHandle_t &handle)¶

This operation requests the middleware to delete the data (the actual deletion is postponed until there is no more use for that data in the whole system). In general, applications are made aware of the deletion by means of operations on the DataReader objects that already knew that instance. This operation does not modify the value of the instance. The instance parameter is passed just for the purposes of identifying the instance. When this operation is used, the Service will automatically supply the value of the source_timestamp that is made available to DataReader objects by means of the source_timestamp attribute inside the SampleInfo. The constraints on the values of the handle parameter and the corresponding error behavior are the same specified for the unregister_instance operation.

Parameters:

data – [in] Sample used to deduce instance’s key in case of handle parameter is HANDLE_NIL.
handle – [in] InstanceHandle of the data

Returns:

RETCODE_PRECONDITION_NOT_MET if the handle introduced does not match with the one associated to the data, RETCODE_OK if the data is correctly sent and RETCODE_ERROR otherwise.

ReturnCode_t dispose_w_timestamp(const void *const instance, const InstanceHandle_t &handle, const fastdds::dds::Time_t &timestamp)¶

This operation performs the same functions as dispose except that the application provides the value for the source_timestamp that is made available to DataReader objects by means of the source_timestamp attribute inside the SampleInfo.

The constraints on the values of the handle parameter and the corresponding error behavior are the same specified for the dispose operation.

This operation may return RETCODE_PRECONDITION_NOT_MET and RETCODE_BAD_PARAMETER under the same circumstances described for the dispose operation.

This operation may return RETCODE_TIMEOUT and RETCODE_OUT_OF_RESOURCES under the same circumstances described for the write operation.

Parameters:

instance – Sample used to deduce instance’s key in case of handle parameter is HANDLE_NIL.
handle – Instance’s key to be disposed.
timestamp – Time_t used to set the source_timestamp.

Returns:

FASTDDS_EXPORTED_API

ReturnCode_t get_liveliness_lost_status(LivelinessLostStatus &status)¶

Returns the liveliness lost status.

Parameters:: status – Liveliness lost status struct
Returns:: RETCODE_OK

const Publisher *get_publisher() const¶

Getter for the Publisher that creates this DataWriter.

Returns:: Pointer to the Publisher

ReturnCode_t assert_liveliness()¶

This operation manually asserts the liveliness of the DataWriter. This is used in combination with the LivelinessQosPolicy to indicate to the Service that the entity remains active. This operation need only be used if the LIVELINESS setting is either MANUAL_BY_PARTICIPANT or MANUAL_BY_TOPIC. Otherwise, it has no effect.

Note

Writing data via the write operation on a DataWriter asserts liveliness on the DataWriter itself and its DomainParticipant. Consequently the use of assert_liveliness is only needed if the application is not writing data regularly.

Returns:: RETCODE_OK if asserted, RETCODE_ERROR otherwise

ReturnCode_t get_matched_subscription_data(SubscriptionBuiltinTopicData &subscription_data, const InstanceHandle_t &subscription_handle) const¶

Retrieves in a subscription associated with the DataWriter.

Warning

Not supported yet. Currently returns RETCODE_UNSUPPORTED

Parameters:

subscription_data – [out] subscription data struct
subscription_handle – InstanceHandle_t of the subscription

Returns:

RETCODE_OK

ReturnCode_t get_matched_subscriptions(std::vector<InstanceHandle_t> &subscription_handles) const¶

Fills the given vector with the InstanceHandle_t of matched DataReaders.

Warning

Not supported yet. Currently returns RETCODE_UNSUPPORTED

Parameters:: subscription_handles – [out] Vector where the InstanceHandle_t are returned
Returns:: RETCODE_OK

ReturnCode_t clear_history(size_t *removed)¶

Clears the DataWriter history.

Parameters:: removed – size_t pointer to return the size of the data removed
Returns:: RETCODE_OK if the samples are removed and RETCODE_ERROR otherwise

ReturnCode_t loan_sample(void *&sample, LoanInitializationKind initialization = LoanInitializationKind::NO_LOAN_INITIALIZATION)¶

Get a pointer to the internal pool where the user could directly write.

This method can only be used on a DataWriter for a plain data type. It will provide the user with a pointer to an internal buffer where the data type can be prepared for sending.

When using NO_LOAN_INITIALIZATION on the initialization parameter, which is the default, no assumptions should be made on the contents where the pointer points to, as it may be an old pointer being reused. See LoanInitializationKind for more details.

Once the sample has been prepared, it can then be published by calling write. After a successful call to write, the middleware takes ownership of the loaned pointer again, and the user should not access that memory again.

If, for whatever reason, the sample is not published, the loan can be returned by calling discard_loan.

Parameters:

sample – [out] Pointer to the sample on the internal pool.
initialization – [in] How to initialize the loaned sample.

Returns:

RETCODE_ILLEGAL_OPERATION when the data type does not support loans.

Returns:

RETCODE_NOT_ENABLED if the writer has not been enabled.

Returns:

RETCODE_OUT_OF_RESOURCES if the pool has been exhausted.

Returns:

RETCODE_OK if a pointer to a sample is successfully obtained.

ReturnCode_t discard_loan(void *&sample)¶

Discards a loaned sample pointer.

See the description on loan_sample for how and when to call this method.

Parameters:: sample – [inout] Pointer to the previously loaned sample.
Returns:: RETCODE_ILLEGAL_OPERATION when the data type does not support loans.
Returns:: RETCODE_NOT_ENABLED if the writer has not been enabled.
Returns:: RETCODE_BAD_PARAMETER if the pointer does not correspond to a loaned sample.
Returns:: RETCODE_OK if the loan is successfully discarded.

ReturnCode_t get_sending_locators(rtps::LocatorList &locators) const¶

Get the list of locators from which this DataWriter may send data.

Parameters:: locators – [out] LocatorList where the list of locators will be stored.
Returns:: NOT_ENABLED if the reader has not been enabled.
Returns:: OK if a list of locators is returned.

ReturnCode_t wait_for_acknowledgments(const void *const instance, const InstanceHandle_t &handle, const fastdds::dds::Duration_t &max_wait)¶

Block the current thread until the writer has received the acknowledgment corresponding to the given instance. Operations performed on the same instance while the current thread is waiting will not be taken into consideration, i.e. this method may return RETCODE_OK with those operations unacknowledged.

Parameters:

instance – Sample used to deduce instance’s key in case of handle parameter is HANDLE_NIL.
handle – Instance handle of the data.
max_wait – Maximum blocking time for this operation.

Returns:

RETCODE_NOT_ENABLED if the writer has not been enabled.

Returns:

RETCODE_BAD_PARAMETER if instance is not a valid pointer.

Returns:

RETCODE_PRECONDITION_NOT_MET if the topic does not have a key, the key is unknown to the writer, or the key is not consistent with handle.

Returns:

RETCODE_OK if the DataWriter received the acknowledgments before the time expired.

Returns:

RETCODE_TIMEOUT otherwise.

ReturnCode_t get_publication_builtin_topic_data(PublicationBuiltinTopicData &publication_data) const¶

Retrieve the publication data discovery information.

Parameters:: publication_data – [out] The publication data discovery information.
Returns:: NOT_ENABLED if the writer has not been enabled.
Returns:: OK if the publication data is returned.

ReturnCode_t set_sample_prefilter(std::shared_ptr<IContentFilter> prefilter)¶

Set a sample prefilter to be used. This filter is always evaluated before sending the sample to any DataReader and prior to any content filtering. Passing a nullptr disables prefiltering.

Note

Prefiltering is currently incompatible with DataSharing.

Parameters:: prefilter – The prefilter to be set.
Returns:: RETCODE_OK if the prefilter is set correctly.