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access to preallocated block of memory?

I am running python on VxWorks. In the course of operation, a vxworks
tasks writes to a reserved area of memory. I need access to this chunk
of memory from within python. Initially I thought I could simply
access it as a string but a string would reallocate and copy this chunk
of memory; which is not something I can have as it would waste a huge
amount of memory. We're talking about something like 40MB on a device
with limited RAM. I have been looking at array. It looks promising.
What's the best route to go here? Ideally, I would like to simply pass
in the address of the reserved block and a length, and have the memory
accessible.

Is there some existing python object/facility I can use or will I need
to create a custom module? Any tips, hints, or pointers would
certainly be appreciated!
Thanks,

Greg

Dec 14 '05
14 2435
Greg Copeland:
I already have access to the block on memory...I
simply need information about existing python facilities which will
allow me to expose the block to python as a native type...from which I
can read byte for byte and optionally write to. As I originally said,
I have a pointer and the block's length. I have access to it already.
I simply need to expose it to python. What facilities already exist to
allow this which do not cause malloc/memcpy on said block?


There is no generic array.at(addres s,length) in core Python as it
would be a hole in Python's type system, allowing reading from or
writing to any memory location and thus making it easier for Python to
cause memory corruption and crashes. Libraries such as ctypes or its
predecessor calldll do allow such access on some operating systems but
not VxWorks. It would be quicker to write a special-purpose library for
your job rather than port ctypes.

Neil
Dec 15 '05 #11
Dang it. That's what I suspected. Thanks!

Greg

Dec 15 '05 #12

You might want to take a look at the "Blocks and Views" code I did,
take a look at it and see if you can either use it directly or use
it with any changes you feel like making.
http://members.dsl-only.net/~daniels/Block.html
--
-Scott David Daniels
sc***********@a cm.org
Dec 16 '05 #13
That certainly looks interesting. I'll check it out right now.

Thanks!

Greg

Dec 16 '05 #14
What license does the code use? The PKG-INFO file says its MIT? This
accurate? I'm still looking over the code, but it looks like I can do
exactly what I need with only minor changes.

Dec 16 '05 #15

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