On Tuesday, 18 December 2018 at 01:34:00 UTC, H. S. Teoh wrote:
I'm not sure I understand what you mean by "globals"; AFAICT
MmFile just has a bunch of member variables, most of which are
only important on the initial mapping and later unmapping.
Once you get a T[] out of MmFile, there's little reason to use
the MmFile object directly anymore until you're done with the
mapping.
Even if you were to use it only once, you would still have to
create all those variables and keep them around untill you no
longer use the slice. While with Elembuf, you only need to keep
the slice.
In std.mmfile OpSlice returns a void[] instead of a T[],
making it difficult to work with as it requires a cast, there
would also be a need to do costly conversions should "T.sizeof
!= void.sizeof" be true.
Are you sure? Casting void[] to T[] only needs to be done once,
and the only cost is recomputing .length. (Casting an array
does *not* make a copy of the elements or anything of that
sort, btw.) Once you have a T[], it's pointless to call
Mmfile.opSlice again; just slice the T[] directly.
I was assuming that you were using mmfile directly. Yes, it is
possible to just use the output, but the benefit I see from
Elembuf is that you can use it directly without too much
overhead, but you can also just take a slice and refill when
needed as well. While the focus of this library is in socket
receival, reading from a file doesn't seem to be bad either.
Although if you are intending on sending the file through a
socket to another computer, use splice
instead.(http://man7.org/linux/man-pages/man2/splice.2.html)
However, from purely a code perspective Elembuf attempts to
have minimal runtime arguments and variables, with heavy
reliance on compile time arguments. It also uses a newer
system call for Linux (Glibc) that is currently not in
druntime, the reason for this system call is that it allows
for faster buffer construction. Read more about it here:
https://dvdhrm.wordpress.com/2014/06/10/memfd_create2/
Hmm. Isn't that orthogonal to mmap(), though? You could just
map a
memfd descriptor using mmap() to achieve essentially equivalent
functionality. Am I missing something obvious?
The main point from the post linked earlier is that using
memfd_create instead of shm_open has many benefits. While it may
not directly affect how files are read into memory,as mmfile is
using open, it is still interesting to know when benchmarking
your options. If you are writing the whole file into memory, then
this library may be a better option for you just purely for the
sake of saving memory. If you are not doing that and instead
using file mmap with an offset, then benchmarking would give you
the best answer.
