| Re: dynamic memory in call_external [message #14157] |
Tue, 26 January 1999 00:00 |
Vapuser
Messages: 63
Registered: November 1998
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Member |
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David Foster <foster@bial1.ucsd.edu> writes:
Thanks to all that answered. I should've been a little more clear in
the question, however. The variables that will be created in this
person's routine will be local to the CALL_EXTERNAL routine and will
be passed neither into nor out of the routine. Looks like the answer
to the first question is 'yes' provided that the error handling always
assures that the memory is returned in case of error. I suspected the
answer to the second was 'no' and am confirmed in that answer.
WHD
> Vapuser wrote:
>>
>> I have someone in my office who wants to know:
>>
>> Is it advisable to create and destroy memory within a CALL_EXTERNAL
>> routine? (that is, can one safely use malloc and free?) Or must one
>> make the routine(s) in question LINKIMAGE routines and the idl memory
>> management routines (IDL_MEMAlloc, IDL_MEMfree and IDL_GetScratch)
>> available in that environment.
>
> I have used [m|c]alloc() and free() in CALL_EXTERNAL modules with no
> problems, usually for relatively small chunks of memory. But of course
> this is only for variables within the C module; you can't allocate
> memory within the C module and pass it back to IDL.
>
> Dave
> --
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
> David S. Foster Univ. of California, San Diego
> Programmer/Analyst Brain Image Analysis Laboratory
> foster@bial1.ucsd.edu Department of Psychiatry
> (619) 622-5892 8950 Via La Jolla Drive, Suite 2240
> La Jolla, CA 92037
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
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| Re: dynamic memory in call_external [message #14163 is a reply to message #14157] |
Tue, 26 January 1999 00:00  |
David Foster
Messages: 341
Registered: January 1996
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Senior Member |
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Mark Rivers wrote:
>
> In article <88lnirufne.fsf@catspaw.jpl.nasa.gov>, Vapuser <vapuser@catspaw.jpl.nasa.gov> writes:
>>
>>
>> I have someone in my office who wants to know:
>>
>> Is it advisable to create and destroy memory within a CALL_EXTERNAL
>> routine? (that is, can one safely use malloc and free?) Or must one
>> make the routine(s) in question LINKIMAGE routines and the idl memory
>> management routines (IDL_MEMAlloc, IDL_MEMfree and IDL_GetScratch)
>> available in that environment.
>
> No, you should not create and destroy memory within CAll_EXTERNAL. The reason
> is that when you use CALL_EXTERNAL you are passed only the address of the data
> storage part of the IDL variable. You are not passed other important pieces of
> information for that variable, such as how big it is, what the data type is,
> etc. If you create and destroy memory you will only change the pointer, but
> not the other descriptive information. It might work OK if you are sure you
> won't change the size or type of the IDL variable, but I would not bet on it.
>
I think we should be clear what we are talking about. I believe the
question was whether one can safely use malloc() and free() to
allocate and free memory *within* a CALL_EXTERNAL module, and the
answer to this is yes. But you cannot allocate memory for variables
that you intend to pass back to IDL (the well-known rule that you
have to allocate all arguments before passing them to CALL_EXTERNAL).
If we don't clarify this distinction I think people will get confused.
Dave
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
David S. Foster Univ. of California, San Diego
Programmer/Analyst Brain Image Analysis Laboratory
foster@bial1.ucsd.edu Department of Psychiatry
(619) 622-5892 8950 Via La Jolla Drive, Suite 2240
La Jolla, CA 92037
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
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| Re: dynamic memory in call_external [message #14169 is a reply to message #14157] |
Tue, 26 January 1999 00:00 |
rivers
Messages: 228
Registered: March 1991
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Senior Member |
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In article <88lnirufne.fsf@catspaw.jpl.nasa.gov>, Vapuser <vapuser@catspaw.jpl.nasa.gov> writes:
>
>
> I have someone in my office who wants to know:
>
> Is it advisable to create and destroy memory within a CALL_EXTERNAL
> routine? (that is, can one safely use malloc and free?) Or must one
> make the routine(s) in question LINKIMAGE routines and the idl memory
> management routines (IDL_MEMAlloc, IDL_MEMfree and IDL_GetScratch)
> available in that environment.
No, you should not create and destroy memory within CAll_EXTERNAL. The reason
is that when you use CALL_EXTERNAL you are passed only the address of the data
storage part of the IDL variable. You are not passed other important pieces of
information for that variable, such as how big it is, what the data type is,
etc. If you create and destroy memory you will only change the pointer, but
not the other descriptive information. It might work OK if you are sure you
won't change the size or type of the IDL variable, but I would not bet on it.
> Secondly, can one create an array in IDL (in the interpreter) that
> is page aligned (i.e. as if one had done it using the 'valloc' version
> of malloc in C) which can then be passed down into the CALL_EXTERNAL
> routine.
I don't think so.
____________________________________________________________
Mark Rivers (773) 702-2279 (office)
CARS (773) 702-9951 (secretary)
Univ. of Chicago (773) 702-5454 (FAX)
5640 S. Ellis Ave. (708) 922-0499 (home)
Chicago, IL 60637 rivers@cars.uchicago.edu (e-mail)
or:
Argonne National Laboratory (630) 252-0422 (office)
Building 434A (630) 252-0405 (lab)
9700 South Cass Avenue (630) 252-1713 (beamline)
Argonne, IL 60439 (630) 252-0443 (FAX)
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| Re: dynamic memory in call_external [message #14170 is a reply to message #14157] |
Tue, 26 January 1999 00:00 |
korpela
Messages: 59
Registered: September 1993
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Member |
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In article <88lnirufne.fsf@catspaw.jpl.nasa.gov>,
Vapuser <vapuser@catspaw.jpl.nasa.gov> wrote:
>
> Is it advisable to create and destroy memory within a CALL_EXTERNAL
> routine? (that is, can one safely use malloc and free?)
These are actually two separate questions. The answer to the second is
"yes," one can safely use malloc and free from a call_external routine.
IDL uses malloc and free for its memory allocations (at least in the
UNIX versions). The answer to the first question is "maybe not." Some
of the RSI domeumentation claims that this can lead to more memory
fragmentation than using IDL's allocation routines would. However I
cannot easily imagine a case in which this would happen, unless IDL
depends upon behavior of realloc that is not guaranteed to occur.
> Secondly, can one create an array in IDL (in the interpreter) that
> is page aligned (i.e. as if one had done it using the 'valloc' version
> of malloc in C) which can then be passed down into the CALL_EXTERNAL
> routine.
Not that I am aware of.
Eric
--
Eric Korpela | An object at rest can never be
korpela@ssl.berkeley.edu | stopped.
<a href="http://sag-www.ssl.berkeley.edu/~korpela">Click for home page.</a>
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| Re: dynamic memory in call_external [message #14172 is a reply to message #14157] |
Mon, 25 January 1999 00:00 |
David Foster
Messages: 341
Registered: January 1996
|
Senior Member |
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Vapuser wrote:
>
> I have someone in my office who wants to know:
>
> Is it advisable to create and destroy memory within a CALL_EXTERNAL
> routine? (that is, can one safely use malloc and free?) Or must one
> make the routine(s) in question LINKIMAGE routines and the idl memory
> management routines (IDL_MEMAlloc, IDL_MEMfree and IDL_GetScratch)
> available in that environment.
I have used [m|c]alloc() and free() in CALL_EXTERNAL modules with no
problems, usually for relatively small chunks of memory. But of course
this is only for variables within the C module; you can't allocate
memory within the C module and pass it back to IDL.
Dave
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
David S. Foster Univ. of California, San Diego
Programmer/Analyst Brain Image Analysis Laboratory
foster@bial1.ucsd.edu Department of Psychiatry
(619) 622-5892 8950 Via La Jolla Drive, Suite 2240
La Jolla, CA 92037
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
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