Jen,
I would not be shocked at incompatibilities in the system described making it
hard to exchange anything, including text, but am not clear if there is a
limitation of four bytes in what can be shared. For me, a character string can
use any number of contiguous bytes in memory that some kind of pointer or table
lookup provides access to.
Clearly you could squeeze larger number in by not writing decimals but using
hexadecimal notation that adds a to f as valid entries, and of course you can
make your own customized base 32 or if you use more symbols (such as upper and
lower case as different) you could add a few symbols and stretch it out to
base 60 or 64.
Like I said, I may have missed something. If you KNOW that system A will
interact with systems B and C and so on, and each machine knows what kind it
is, and especially if it knows which kind of machine left it something in
shared memory, there has to be a way to coordinate between them. If character
strings in ASCII or UTF8 or EBCDIC or some kind of raw are allowed, and used
with just a few characters that can spell out numbers, I would think much is
possible. If needed, perhaps a fixed size could be set aside and the string use
a null terminator if shorter.
Of course if this big-endian issue also scrambles bytes used in strings, forget
it.
Or, maybe shared memory is not the easy way to go, even it it might be faster.
-----Original Message-----
From: Jen Kris <jenk...@tutanota.com>
To: Avi Gross <avigr...@verizon.net>
Cc: python-list@python.org <python-list@python.org>
Sent: Wed, Feb 2, 2022 1:27 pm
Subject: Re: Data unchanged when passing data to Python in multiprocessing
shared memory
An ASCII string will not work. If you convert 32894 to an ascii string you
will have five bytes, but you need four. In my original post I showed the C
program I used to convert any 32-bit number to 4 bytes.
Feb 2, 2022, 10:16 by python-list@python.org:
I applaud trying to find the right solution but wonder if a more trivial
solution is even being considered. It ignores big and little endians and just
converts your data into another form and back.
If all you want to do is send an integer that fit in 32 bits or 64 bits, why
not convert it to a character string in a form that both machines will see the
same way and when read back, convert it back to an integer?
As long as both side see the same string, this can be done in reasonable time
and portably.
Or am I missing something? Is "1234" not necessarily seen in the same order, or
"1.234e3" or whatever?
Obviously, if the mechanism is heavily used and multiple sides keep reading and
even writing the same memory location, this is not ideal. But having different
incompatible processors looking at the same memory is also not.
-----Original Message-----
From: Dennis Lee Bieber <wlfr...@ix.netcom.com>
To: python-list@python.org
Sent: Wed, Feb 2, 2022 12:30 am
Subject: Re: Data unchanged when passing data to Python in multiprocessing
shared memory
On Wed, 2 Feb 2022 00:40:22 +0100 (CET), Jen Kris <jenk...@tutanota.com>
declaimed the following:
breakup = int.from_bytes(byte_val, "big")
>print("this is breakup " + str(breakup))
>Python prints: this is breakup 32894
>Note that I had to switch from little endian to big endian. Python is little
>endian by default, but in this case it's big endian.
Look at the struct module. I'm pretty certain it has flags for big or
little end, or system native (that, or run your integers through the
various "network byte order" functions that I think C and Python both
support.
https://www.gta.ufrj.br/ensino/eel878/sockets/htonsman.html
>However, if anyone on this list knows how to pass data from a non-Python
>language to Python in multiprocessing.shared_memory please let me (and the
>list) know.
<pondering>MMU cache lines not writing through to RAM? Can't find
anything on Google to force a cache flush</pondering> Can you test on a
different OS? (Windows vs Linux)
--
Wulfraed Dennis Lee Bieber AF6VN
wlfr...@ix.netcom.com http://wlfraed.microdiversity.freeddns.org/
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