That's a good question, Bill, and I don't know the answer. I have not
tried it under Windows: maybe it doesn't work there? It works on the
Mac.
At the end of a run, both processes show similar displays with: showmap_jmf_'' :
showmap_jmf_''
┌──────────┬───────────────────────────────────────┬───────────────────────────────────────┬──┬────┬─────────┬─────────┬──┬─────┬──────┐
│name │fn │sn
│fh│mh │address │header │ts│msize│refs │
├──────────┼───────────────────────────────────────┼───────────────────────────────────────┼──┼────┼─────────┼─────────┼──┼─────┼──────┤
│CTL0_base_│/Users/ianclark/j602-user/temp/ctl0.jmf│/Users/ianclark/j602-user/temp/ctl0.jmf│44│1284│549224448│549224448│
│1000 │200029│
├──────────┼───────────────────────────────────────┼───────────────────────────────────────┼──┼────┼─────────┼─────────┼──┼─────┼──────┤
│CTL1_base_│/Users/ianclark/j602-user/temp/ctl1.jmf│/Users/ianclark/j602-user/temp/ctl1.jmf│45│1284│559734784│559734784│
│1000 │200029│
└──────────┴───────────────────────────────────────┴───────────────────────────────────────┴──┴────┴─────────┴─────────┴──┴─────┴──────┘
I shall try generalizing it to more than 2 processes. That would be
diagnostic. I observe in passing that each process <n> writes to its
own CTL<n> and no other does. If more than one process wrote to a
given CTL<n>, I'd anticipate a crash. Maybe all processes should
access via share_jmf_ instead of map_jmf_, else vital protection is
lost? The system is disturbingly symmetrical, with no one process
apparently "owning" any of the mapped nouns (whatever that really
means). Even if it finds CTL<n> absent and creates it with create_jmf_
-that still does not give it any noticeable "ownership".
On Sun, Jan 8, 2012 at 7:17 AM, bill lam <bbill....@gmail.com> wrote:
> Ian,
>
> I have not study the source carefully, but at the first glance, it seemed
> that two running J processes accessing the same mapped file. Why
> share_jmf_ was not needed? Please correct me if I missed anything.
>
> Вск, 08 Янв 2012, Ian Clark писал(а):
>> This is my eventual solution to the "are you alive?" problem:
>>
>> http://www.jsoftware.com/jwiki/Scripts/AliveDemo
>>
>> It doesn't use sockets, but a couple of mapped files instead. The
>> (identically coded) processes use them to play pat-a-cake.
>>
>> For demo simplicity I've coded a 'hard' duty cycle (a while.-loop.)
>> rather than one I find much more convenient: a "soft" duty cycle that
>> posts an event calling itself again after a given interval.
>>
>> A "soft" duty cycle has a lot of advantages. You have to play with the
>> alternatives to appreciate them, but the main ones are that it dies
>> gracefully if there's a code error, and it doesn't lock the session
>> window and any UI which the duty cycle happens to be managing. Indeed
>> the duty cycle runs in the background, keeping all displays up-to-date
>> and leaving you (almost) full use of J facilities.
>>
>> I'll place a "soft" duty cycle code sample on the wiki in a day or two.
>>
>> On Mon, Jan 2, 2012 at 6:51 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
>
> --
> regards,
> ====================================================
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> gpg --keyserver subkeys.pgp.net --recv-keys 4434BAB3
> ----------------------------------------------------------------------
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