Thanks, Raul. I'll look again at the sockets solution. Some time since I ran that lab, but I seem to recall it had a timer to poll the link hidden somewhere, so I think I dismissed it from my mind for that reason. IMO it's as clunky as my other solutions: certainly clunkier than the yellow-J approach. One good thing was the ability of one process to send a "message" triggering a callback in the other process. Specifically to execute a given J sentence. That would solve most things. But is it a proper message, placed in the system's event queue, or something the other process has to poll for?
A message "are you alive?" sent via a socket would surely need a timeout to register the answer "no"? A pair of mapped files might provide the nearest thing to my recollection of 1970's-style "common memory". In the days before it was deemed vital to build Chinese walls between asynchronous processes. If each process updates a timestamp in its mapped file, then a simple match (-:) would verify the other process is (still) running. You wouldn't even need mapped files: just read the directory timestamps. Both process, I might add, are already having to run their own timer-driven duty-cycles for other purposes. Oh for a system "heartbeat", which could trigger an "Idle" event in any given process! On Mon, Jan 2, 2012 at 6:59 PM, Raul Miller <rauldmil...@gmail.com> wrote: > I think I would use (non-blocking) sockets for this. > > If you are using j6, I'd point you at the socket labs, which > demonstrate their use. I am not sure what state those labs are in for > j7. > > -- > Raul > > On Mon, Jan 2, 2012 at 1:51 PM, Ian Clark <earthspo...@gmail.com> wrote: >> Please forgive these questions I post to the list to which I know the >> answer. Or rather: *an* answer. I learn a lot from others' responses. >> Even if it's "my way is best after all" -- that's a valuable thing to >> know. >> >> I have two separate J processes running (assume Linux / Darwin, though >> I'm keen on cross-platform solutions). They communicate by each >> writing a text file which is read by the other >> (keep-it-simple-stupid). Is there a neat, robust way of one process >> asking the other: "are you there?" or "are you still alive?" >> >> I'm au-fait with how the yellow-J works, all the solutions involving >> timer-driven duty-cycles, timeouts, and reading files written by the >> sister process, Or the files' timestamps, or permissions. But these >> all seem so clunky. I guess what I want is something that was so easy >> in the 1970s but is so awkward on today's machines: just reserve a >> pair of bits in absolute memory -- or a pair of pixels on the screen >> -- or some inessential system flags -- and play pat-a-cake with them. >> >> Once upon a time there was such a thing as "common memory". >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
