[LCP] mapping memory

[Mark Farnell]

I see,

So you mean that I let *each thread* to open the shared memory object,
the each thread can use the FD given to make its own memory map and
make mprotect() calls?

Am I correct?  If so, then that's great!  Thanks a lot!

Cheers,

Mark

On Tue, Nov 4, 2008 at 3:03 PM, Kim Hawtin <kim.hawtin at adelaide.edu.au> wrote:
> Hi Mark,
>
> Mark Farnell wrote:
>> I mean different logical address.
>>
>> In a process, suppose I malloc a piece a memory
>>
>> #define SIZE 1024
>>
>> void *a = malloc(SIZE);
>>
>> Are there any functions which produces a logical mapping of the chunk
>> I've malloced on a *different* address space (but in fact point to the
>> same chunk)
>>
>> void *b = map(a, size);
>>
>> so that b is the base address of a different block (address looks
>> different to a), yet if a thread changes the content pointed to b, it
>> actually maps to the block pointed to by a.
>>
>> The application is that I have a process which spawns multiple POSIX
>> threads.  The process malloc's a piece of memory.  Then what I intend
>> to do is that for each thread, map that piece of memory to a different
>> address space, each mapping can have individual mprotect operations
>> that does not affect other mappings owned by other threads.
>>
>> However if a mapping is written to, it actually writes to the piece of
>> memory malloc'ed by the master.
>>
>> So memcpy etc will *not* do the job.  I am not asking how to copy contents.
>>
>> Can this be done?
>
> inter-process stuff may be better covered by POSIX shared memory.
> eg; http://linux.about.com/library/cmd/blcmdl3_shm_open.htm
>
> alternatively, mmap might be useful, depends on your application;
> eg; http://linux.about.com/library/cmd/blcmdl2_mmap.htm
>
> otherwise start here =0
> http://www.google.com.au/search?hl=en&q=posix+shared+memory+linux
>
> regards,
>
> Kim
> --
> Operating Systems, Services and Operations
> Information Technology Services, The University of Adelaide
> kim.hawtin at adelaide.edu.au
>
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