Mail Archives: pgcc/1999/07/26/14:24:15
On Mon, 26 Jul 1999, Gordon K. Stone wrote:
>
> I have a program in which a number of executables use an mmap'ed file
> to share memory. This used to work fine, but we updated to Redhat ver
> 5.2, and now the changes made by one process are no longer seen by the
> others.
>
> I am using the MAP_FIXED flag--the mmap'ed memory contains absolute
> pointers.
>
> The program has two possible interfaces, an X interface and a console
> interface. Everything appears to work okay when using the X interface.
> It's under the console interface that the problem appears.
>
> Any ideas? Is mmap() different?
I am not quite sure, but IMHO you have to specify the MAP_SHARED option:
reading from man mmap(2):
MAP_SHARED: Share this mapping with all other processes that map this
object.
MAP_PRIVATE: Create a private copy-on-write mapping
You must specify exactly one of MAP_SHARED and MAP_PRIVATE
I do not know whether or not this existed in previous versions (should
exist since this is POSIX.1b) but with this option everything works fine
for me (under RedHat/Mandrake 6.0) and for a friend of mine (RedHat 5.2)
I cannot explain the difference in behavior under X/console, yet maybe
the X code uses this flag ?
>
> Sincerely
>
>
> Gordon Stone
> Technical Support
> Aptech Systems, Inc
> 23804 S.E. Kent-Kangley RD
> Maple Valley, WA 98038
> 425-432-7855 voice
> 425-432-7832 fax
> gordon AT aptech DOT com
>
signed
Robert
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