Function rcl_count_subscribers

Function Documentation

rcl_ret_t rcl_count_subscribers(const rcl_node_t *node, const char *topic_name, size_t *count)

Return the number of subscriptions on a given topic.

The node parameter must point to a valid node.

The topic_name parameter must not be NULL, and must not be an empty string. It should also follow the topic name rules.

See: https://design.ros2.org/articles/topic_and_service_names.html

The count parameter must point to a valid bool. The count parameter is the output for this function and will be set.

In the event that error handling needs to allocate memory, this function will try to use the node’s allocator.

The topic name is not automatically remapped by this function. If there is a subscriber created with topic name foo and remap rule foo:=bar then calling this with topic_name set to bar will return a count of 1, and with topic_name set to foo will return a count of 0. /sa rcl_remap_topic_name()

Attribute

Adherence

Allocates Memory

No

Thread-Safe

No

Uses Atomics

No

Lock-Free

Maybe [1]

[1] implementation may need to protect the data structure with a lock

Parameters:

  • node – [in] the handle to the node being used to query the ROS graph

  • topic_name – [in] the name of the topic in question

  • count – [out] number of subscriptions on the given topic

Returns:

RCL_RET_OK if the query was successful, or

Returns:

RCL_RET_NODE_INVALID if the node is invalid, or

Returns:

RCL_RET_INVALID_ARGUMENT if any arguments are invalid, or

Returns:

RCL_RET_ERROR if an unspecified error occurs.