In Activity Monitor on OS X, it is possible to add additional columns to the process list view. Two columns available in that list are "Messages Sent" and "Messages Received", which show up as "Sent Msgs" and "Rcvd Msgs", respectively. Witness:
What kind of "messages" is Activity Monitor referring to?
When I saw "message", I thought at first of Objective-C "messages" that are dispatched with
objc_msgSend(), but I can't see how those would be tracked by the operating system since most of those messages would be internal to the process itself. A debugger might track those kinds of messages when attached, but I can't see the OS doing it all the time — very high overhead.
So I am guessing those are heavier-weight messages. Are they a form of RPC between processes? Or, are those messages calls from user-land into the kernel? Seeking definitive references. Thank you.