What is the purpose of these functions prefixed by "msg_" in PHP?

Question

As I quoted in my previous question on traffic lights, I had a question regarding to that answer, because when the author of the answer quotes about Traffic lights, he references this documentation link where we have several functions in PHP with the prefix msg_.

I have the slight impression that this refers to message queues, but wanted to confirm the usefulness of this in PHP, since the documentation is not very clear on the utilities of the functions.

Someone could explain for example what are the purposes of these functions below?

msg_receive 
msg_remove_queue 
msg_send 
msg_set_queue 
msg_stat_queue

Answer 1

According to the documentation, within the set of specific functions for process control, this function library has the purpose to provide functionalities to work with System V IPC.

You can manipulate message queues, traffic lights and shared memory through these functions.

Specifically talking about prefixed functions msg_, are functions used to work with message queues, using IPC.

These functions are only available under Linux Operating System.

I made that gist as an example, but I will soon set a better example here.