Re: Mmap question


laziness, impatience, and hubris
	PerlMonks

Re: Mmap question

by Aristotle (Chancellor)

on Jan 31, 2005 at 00:26 UTC ( [id://426465]=note: print w/replies, xml )

Need Help??

in reply to Mmap question

You misunderstood. $shmid is the wrong name, you are getting the address of the mmapped area, not a shared memory ID. mmap(2) has nothing to do with the SysV IPC facilities.

I am not entirely certain on how to use mmap(2) as an alternative to shared memory, since I've never done that, but my reading of the docs and manpage suggest that it is limited to passing down the mmap to child processes on fork. I could be wrong here though, as I said, since I've never tried to use the facility in that capacity.

Makeshifts last the longest.

Comment on Re: Mmap question

Replies are listed 'Best First'.

Re^2: Mmap question
by leriksen (Curate) on Jan 31, 2005 at 00:46 UTC

And zentara I think your right about the octal to decimal conversion.

As for using mmap(2) for IPC, Stevens demonstrates a technique for mmap across related processes (you cant use mmap across unrelated processes, because the address is for that process family. If an unrelated process tries to use it, you'll get a SIGSEGV or SIGBUS core dump). He creates a mmap'd area from /dev/zero, then has co-operating parent and child increment a long integer in turn.

Stevens last word on mmap and shared memory is "If shared memory is required between unrelated processes, the shmXXX functions must be used"

...it is better to be approximately right than precisely wrong. - Warren Buffet

[reply]

In Section Seekers of Perl Wisdom