How to send and receive messages on a Queue

Let's say we have a //y2018:basic_queue.q file that has the following contents:

package y2018;

message BasicMessage {
  float value;
};

queue BasicMessage basic_queue;

and the corresponding entry in //y2018/BUILD

queue_library(
    name = "basic_queue",
    srcs = [
        "basic_queue.q",
    ],
    visibility = ["//visibility:public"],
)

The following examples assume that you've declared a dependency on //y2018:basic_queue in the relevant BUILD file.

Sending a message

First, include the queue definition that is created from the .q file. This will make the basic_queue variable available.

#include "y2018/basic_queue.q.h"

// Allocate a new message pointer to use. basic_queue is from the include
// statement.
auto new_basic_message = basic_queue.MakeMessage();
new_goal.value = 0.5;

// Send the message on the queue
if (!new_basic_message.Send()) {
  LOG(ERROR, "Failed to send.\n");
}

Receiving a message

Once again, we must include the queue header file to get access to the queue.

#include "y2018/basic_queue.q.h"

Then we can receive a message.

basic_queue.FetchLatest();
if (basic_queue.get()) {
  // We have a valid message ready to be used
  LOG(INFO, "Got a BasicMessage from basic_queue with value %f\n",
      basic_queue->value);
} else {
  // No new message was available
  LOG(ERROR, "No message was received\n");
}