Hi all,
Just a request for thoughts here. I'm at a decision point and I'd like some
fresh thoughts on file access methods. Specifically, using standard file
I/O methods be it CreateFile/ReadFile/WriteFile in the Win32 API directly,
or in the guise of a TFileStream, as compared to Memory-Mapped files.
I've used them all so I'm looking for subtle distinctions here. But once I
make my decision I need to move forward so I'd just like to cover the bases.
I guess the biggest point I'm struggling with is that someone I've read in
the past suggested they liked Memory mapped files because they could use
existing memory related functions rather than file handles. Not sure I see
this as a significant point.
One point that's been made in the past is not needing to handle the file I/O
with memory mapped files, not having to manually handle file buffering. But
then again managing the mapped view window across the file itself isn't much
different than managing a file buffer in my mind.
Richter ("Advanced Windows, 3rd ed.") points out that with memory mapped
files one can access huge files, mapping say an 18EB file into a 32-bit
address space. But TFileStream is (at D7) at least smart enough to use
Int64's for such things to that despite being a signed value leaves
something like 9,223,372,036,849,999,999 on the positive side. 32-bit
Windows itself may still be using 32-bits for such things but even so
functions like SetFilePointer provide a low and high value for effectively
doubling the function's reach. So where's Richter's real advantage for
memory mapped files here?
Ignoring such things as sharing across process boundaries, data commitment,
coherence of multiple views, memory files with out physical storage, and
other advanced concepts, speaking just in terms of file access, file I/O, be
it convenience, performance, or whatever, can anyone make a case for
memory-mapped files over other methods?
TIA,
Jim
------------------------------------------------------------------------
Jim Burns, <mailto:[EMAIL PROTECTED]>
Technology Dynamics
Pearland, Texas USA
281 485-0410 / 281 813-6939
__________________________________________________
Delphi-Talk mailing list -> [email protected]
http://www.elists.org/mailman/listinfo/delphi-talk
