Function rcl_wait_for_publishers

Function Documentation

rcl_ret_t rcl_wait_for_publishers(const rcl_node_t *node, rcl_allocator_t *allocator, const char *topic_name, const size_t count, rcutils_duration_value_t timeout, bool *success)

Wait for there to be a specified number of publishers on a given topic.

The node parameter must point to a valid node. The nodes graph guard condition is used by this function, and therefore the caller should take care not to use the guard condition concurrently in any other wait sets.

The allocator parameter must point to a valid allocator.

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

This function blocks and will return when the number of publishers for topic_name is greater than or equal to the count parameter, or the specified timeout is reached.

The timeout parameter is in nanoseconds. The timeout is based on system time elapsed. A negative value disables the timeout (i.e. this function blocks until the number of publishers is greater than or equals to count).

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

Attribute

Adherence

Allocates Memory

Yes

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

  • allocator – [in] to allocate space for the rcl_wait_set_t used to wait for graph events

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

  • count – [in] number of publishers to wait for

  • timeout – [in] maximum duration to wait for publishers

  • success – [out] true if the number of publishers is equal to or greater than count, or false if a timeout occurred waiting for publishers.

Returns:

RCL_RET_OK if there was no errors, 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_TIMEOUT if a timeout occurs before the number of publishers is detected, or

Returns:

RCL_RET_ERROR if an unspecified error occurred.