| Re: DLM returning a pointer... [message #24869 is a reply to message #24777] |
Tue, 24 April 2001 04:48   |
Randall Skelton
Messages: 169
Registered: October 2000
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Senior Member |
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After reading Craig's email, I am somewhat confused...
What I really need to know is how do I allocate a memory block in my C
function such that I am sure that it cannot be overwritten or otherwise
corrupted. I want a routine that can establish a connection to a given
'port' which requires me to allocate some memory and return a pointer to
this memory block. I then want to be very sure that the memory allocated
is 'safe' while now that I am back in IDL. Then I want to be able to pass
this pointer from IDL back to C so as the database connection must be
established before data can be sent or received. Finally, from IDL I
would close the connection (again requiring me to pass this pointer) and
de-allocate the memory. Obviously, such an implementation is risky as it
could lead to memory leaks in IDL if the programmer fails to close the
connection properly. I am open to other ideas, but I want to separate the
open and close connection functions. I am thinking about putting a
time-out on the connection so that if idle for more than n minutes it
deallocates. I fear, however, that a time-out would likely lead to
problems and would be rather tricky to implement. It would be nice if
there were some way to ensure that there was a matching 'open' and 'close'
connection function with the IDL compiler...
Will the memory allocated with the IDL_GetScratch function span the forked
C process life? i.e. if I use IDL_GetScratch to allocate memory, will IDL
(potentially) cleanup and deallocate the memory before I call
IDL_Deltmp()? What about IDL_MemAlloc and IDL_MemFree? Should I just
consider defining an list say 10 of these structures with IDL_MemAllocPerm
(giving me 10 possible connections) and forget about reclaiming the
memory?
(I am assuming here that since IDL is calling the C program, this is a
unix fork process giving C access to IDL's memory space alone. I am
reluctant to use malloc directly in C as I doubt that IDL would respect
the memory it allocates when I return to IDL).
All comments, suggestions and queries are greatly appreciated!
Randall Skelton
NB: just wait until I start asking how to make this multi threaded with
asynchronous output from simultaneous connections ;)
On Tue, 24 Apr 2001, Martin Schultz wrote:
>>> Hi all,
>>>
>>> I am trying to write a few IDL functions which mirror those of a C library
>>> [...]
>>
>> I don't think it would be wise to return a pointer, although
>> technically it is possible. You could in principle cast the pointer
>> to an integer, and return the integer.
>
> ... you probably meant an unsigned 64-bit value (in IDL speak
> ULONG64).
>
> Martin
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