mmap for IPC

[Jay Braun]

Just want to make sure: If I use mmap for inter-process communication, the processes that share the memory need not be forked from some parent process. They can be invoked independently, correct?

Thank you,
Jay

[Rainer Weikusat]

If you're mmapping a 'publically accessible object', yes.

[Lusotec]

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Yes, if the mapping is not anonymous. If the mapping is anonymous only the
process and its children can access the anonymous mapping (see MAP_ANONYMOUS
in man mmap).

On a side note, you may want to use shm_open instead of mmap directly if you
want to use shared memory for IPC between unrelated processes.

Regards.
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[Rainer Weikusat]

Lusotec <nom...@nomail.not> writes:
> Jay Braun wrote:
>> Just want to make sure: If I use mmap for inter-process communication,
>> the processes that share the memory need not be forked from some parent
>> process. They can be invoked independently, correct?
>
> Yes, if the mapping is not anonymous. If the mapping is anonymous only the
> process and its children can access the anonymous mapping (see MAP_ANONYMOUS
> in man mmap).
>
> On a side note, you may want to use shm_open instead of mmap directly if you
> want to use shared memory for IPC between unrelated processes.

Quoting shm_open(3):

A POSIX shared memory object is in effect a handle which can
be used by unrelated processes to mmap(2) the same region of
shared memory.

[Jasen Betts]

the venerable linux prgogrammer's guide has a good chapter on shared
memory with code examples http://www.tldp.org/LDP/lpg/

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