NSRunningApplication.h: "Not all applications have a pid"

From the com开发者_开发问答ment on processIdentifier in NSRunningApplication.h:

Not all applications have a pid.

Huh?

I can see this happening in the specific case of an NSRunningApplication representing a terminated process (runningProcess.terminated == YES), but I can't think of an example of an running application NOT having a process ID. That's kinda Unix 101.

Documentation bug or am I missing something?

It's a hedge. A "running application" is something that the user thinks of as an application. Shows up in the cmd-tab switcher, etc. That need not necessarily correspond directly to a process. In the classic environment, multiple applications were hosted by a single unix process, classic. In this situation NSRunningApplication would return -1 for each "application".

People who had been at it long enough had seen enough interesting hacks that they thought this was an important thing to define.