On Wed, 4 Jul 2012, Stefan Ring wrote:

I really makes no sense at all to
have munmap(2) not imply msync(3C).

Why not? munmap(2) does basically the equivalent of write(2). In the
case of write, that is: a later read from the same location will see
the written data, unless another write happens in-between. If power

Actually, a write to memory for a memory mapped file is more similar to write(2). If two programs have the same file mapped then the effect on the memory they share is instantaneous because it is the same physical memory. A mmapped file becomes shared memory as soon as it is mapped at least twice.

It is pretty common for a system of applications to implement shared memory via memory mapped files with the mapped memory used for read/write. This is a precursor to POSIX's shm_open(3RT) which produces similar functionality without a known file in the filesystem

Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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