Function rmw_get_subscriber_names_and_types_by_node

Function Documentation

rmw_ret_t rmw_get_subscriber_names_and_types_by_node(const rmw_node_t *node, rcutils_allocator_t *allocator, const char *node_name, const char *node_namespace, bool no_demangle, rmw_names_and_types_t *topic_names_and_types)

Return all topic names and types for which a given remote node has subscriptions.

This function returns an array of topic names and types for which a given remote node has subscriptions, as discovered so far by the given local node.

Attribute

Adherence

Allocates Memory

Yes

Thread-Safe

Yes

Uses Atomics

Maybe [1]

Lock-Free

Maybe [1]

[1] rmw implementation defined, check the implementation documentation

Runtime behavior

To query the ROS graph is a synchronous operation. It is also non-blocking, but it is not guaranteed to be lock-free. Generally speaking, implementations may synchronize access to internal resources using locks but are not allowed to wait for events with no guaranteed time bound (barring the effects of starvation due to OS scheduling).

Thread-safety

Nodes are thread-safe objects, and so are all operations on them except for finalization. Therefore, it is safe to query the ROS graph using the same node concurrently. However, when querying subscribed topic names and types:

  • Access to the array of names and types is not synchronized. It is not safe to read or write topic_names_and_types while rmw_get_subscriber_names_and_types_by_node() uses it.

  • Access to node name and namespace is read-only but it is not synchronized. Concurrent node_name and node_namespace reads are safe, but concurrent reads and writes are not.

  • The default allocators are thread-safe objects, but any custom allocator may not be. Check your allocator documentation for further reference.

Parameters:

  • node – [in] Local node to query the ROS graph.

  • allocator – [in] Allocator to be used when populating the topic_names_and_types array.

  • node_name – [in] Name of the remote node to get information for.

  • node_namespace – [in] Namespace of the remote node to get information for.

  • no_demangle – [in] Whether to demangle all topic names following ROS conventions or not.

  • topic_names_and_types – [out] Array of topic names and types the remote node has created a subscription for, populated on success but left unchanged on failure. If populated, it is up to the caller to finalize this array later on using rmw_names_and_types_fini().

Pre:

Given node must be a valid node handle, as returned by rmw_create_node().

Pre:

Given topic_names_and_types must be a zero-initialized array of names and types, as returned by rmw_get_zero_initialized_names_and_types().

Returns:

RMW_RET_OK if the query was successful, or

Returns:

RMW_RET_INVALID_ARGUMENT if node is NULL, or

Returns:

RMW_RET_INVALID_ARGUMENT if allocator is not valid, by rcutils_allocator_is_valid() definition, or

Returns:

RMW_RET_INVALID_ARGUMENT if node_name is not valid, by rmw_validate_node_name() definition, or

Returns:

RMW_RET_INVALID_ARGUMENT if node_namespace is not valid, by rmw_validate_namespace() definition, or

Returns:

RMW_RET_INVALID_ARGUMENT if topic_names_and_types is NULL, or

Returns:

RMW_RET_INVALID_ARGUMENT if topic_names_and_types is not a zero-initialized array, or

Returns:

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

Returns:

RMW_RET_NODE_NAME_NON_EXISTENT if the node name wasn’t found, or

Returns:

RMW_RET_BAD_ALLOC if memory allocation fails, or

Returns:

RMW_RET_ERROR if an unspecified error occurs.