[REBOL] Re: Looking over the horizon - Rebol 3
From: nitsch-lists:netcologne at: 12-Nov-2003 21:23
Am Mittwoch, 12. November 2003 19:17 schrieb Gregg Irwin:
> Hi Petr,
>
> PK> Maybe off-topic - but some time ago there was mention of so called
> PK> memory-mapped files. What is that?
>
> Under Windows (not sure about other OSs) an MMF (Memory Mapped File)
> is a "view" of a disk file mapped into memory.
That means after mapping the processor can access the filecontent without
doing explicit IO. The file his handled similar to a swapfile then. So the OS
can buffer smarter. Only load stuff when it is touched. if memory is large
enough buffer the whole file, no more io-calls needed then. And
data-structures can be mapped directly on the data in the file, no need for
copying between multiple buffers.
If rebol could map files to strings, we could do
parse map-file %file.txt rule
without special parse-smartness.
> Multiple processes can
> share mappings and so share data in memory--i.e. one can write to the
> MMF and others will see the changes instantly. They can also be used
> to let you write code that operates on disk files without having to
> deal with all the niggling I/O details in a case where the file is too
> large for memory or something. One of the classic examples, IIRC, was
> to use strrev on a MMF to reverse the data on disk, no matter how
> large the disk file was.
>
> Very handy for sharing data between processes. I think most, if not
> all, data sharing APIs map to them under the hood.
>
> -- Gregg
-Volker
