mmapfile uses mmap on unix and MapViewOfFile on Windows to provide a way
of quickly storing and loading data that's already in some kind of in-memory
binary format.
create creates a new file and maps new memory to that file. You can
then write to the memory to write to the file.
open opens an existing file and maps its contents to memory, returning
a pointer to the memory and the length of the file.
close syncs memory to the file, closes the file, and deletes the
mapping between the memory and the file.
malloc maps anonymous memory (not mapped to a file), and so acts like
malloc. The advantage is that we can get memory above 4G, but the BIG
disadvantage is that mmap is not a high-perfomance allocator. Only use this
infrequently for big blocks of memory. It's a nasty hack.
free frees memory mmapped by malloc
The "gc" variants of create, open and malloc (gccreate, gcopen and
gcmalloc) set up a garbage collection callback for the pointer so that the
file is correctly closed when the pointer is no longer referenced. Not
appropriate if you might be storing the pointer in C, referencing it from
unmanaged memory, or casting it to another type!
All memory is mapped above 4G to try to keep away from the memory space LuaJIT uses.
local ffi = require"ffi"
ffi.cdef"struct test { int a; double b; };"
local mmapfile = require"mmapfile"
local ptr1 = mmapfile.gccreate("mmapfile-test", 1, "struct test")
ptr1.a = 1
ptr1.b = 1.5
ptr1 = nil
collectgarbage()
local ptr2, size = mmapfile.gcopen("mmapfile-test", "struct test")
assert(size == 1)
assert(ptr2.a == 1)
assert(ptr2.b == 1.5)
For more details make doc or ldoc lua --all.
- Should probably have an option for directly mapping existing memory, but I don't know enough about page boundaries.