Function rmw_send_request

Function Documentation

rmw_ret_t rmw_send_request(const rmw_client_t *client, const void *ros_request, int64_t *sequence_id)

Send a ROS service request.

Send a ROS service request to one or more service servers, with matching QoS policies, using the given client.

On success, this function will return a sequence number. It is up to callers to save the returned sequence number to pair the ROS service request just sent with future ROS service responses (taken using rmw_take_response()).

Attribute

Adherence

Allocates Memory

Maybe

Thread-Safe

Yes

Uses Atomics

Maybe [1]

Lock-Free

Maybe [1]

[1] implementation defined, check implementation documentation.

Runtime behavior

It is implementation defined whether sending a ROS service request is a synchronous or asynchronous, and blocking or non-blocking, operation. However, asynchronous implementations are not allowed to access the given ROS service request after this function returns. Check the implementation documentation to learn about request behavior.

Memory allocation

It is implementation defined whether memory will be allocated on send or not. For instance, implementations that serialize ROS service requests may need to perform additional memory allocations when dealing with unbounded (dynamically-sized) fields.

Thread-safety

Service clients are thread-safe objects, and so are all operations on them except for finalization. Therefore, it is safe to send requests using the same service client concurrently. However:

  • Access to the given ROS service request is read-only but it is not synchronized. Concurrent ros_request reads are safe, but concurrent reads and writes are not.

  • Access to given primitive data-type arguments is not synchronized. It is not safe to read or write sequence_id while rmw_send_request() uses it.

Note

It is implementation defined how many service servers may get, and potentially react to, the same request, considering there may be more than one server for the same service in the ROS graph.

Parameters:

  • client – [in] Service client to send a request with.

  • ros_request – [in] ROS service request to be sent.

  • sequence_id – [out] Sequence number for the ros_request just sent i.e. a unique identification number for it, populated on success.

Pre:

Given client must be a valid client, as returned by rmw_create_client().

Pre:

Given ros_request must be a valid service request, whose type matches the service type support registered with the client on creation.

Returns:

RMW_RET_OK if successful, or

Returns:

RMW_RET_BAD_ALLOC if memory allocation fails, or

Returns:

RMW_RET_INVALID_ARGUMENT if client is NULL, or

Returns:

RMW_RET_INVALID_ARGUMENT if ros_request is NULL, or

Returns:

RMW_RET_INVALID_ARGUMENT if sequence_id is NULL, or

Returns:

RMW_RET_INCORRECT_RMW_IMPLEMENTATION if the client implementation identifier does not match this implementation, or

Returns:

RMW_RET_ERROR if an unexpected error occurs.