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From: ara.t.howard on 25 Jul 2010 11:24
NAME

nmap (reference ruby class which combines narray and mmap)
na_str (c extension)

REQUIREMENTS

mmap : http://moulon.inra.fr/ruby/mmap.html
narray : http://narray.rubyforge.org/

URIS

http://codeforpeople.com/lib/ruby/nmap/


SYNOPSIS

na_str is designed to allow data sharing between narray object and other ruby
objects. the shared data is that returned by the objects to_s or
to_str method
and rb_string_new4. using this technique memory mapped (using guy's mmap
extensions) data can be altered with no explicit io on the users part and
partial changed to numerical grids can occur very quickly and persistently.

the nmap.rb reference impl is a concrete example of this usage and is
included in the distribution.


EXAMPLE USAGE

jib:~/eg/ruby/na_str > cat a.rb
#
# the nmap extension is installed along with na_str
#
require 'nmap'
#
# the NMap ctor interface is similar to NArray's, but a backing
file must also
# be specified
#
path, x, y = 'int.data', 3, 4
nmap = NMap.int path, x, y
#
# copy the last row to the first
#
nmap.na[true, 0] = nmap.na[true, 3]
#
# set the last row to be the current time. if you run this a few
times you'll
# notice that changes to the narray are automatically written to the to
# backing file via the magic of mmap
#
nmap.na[true, 3] = Time.now.to_i
#
# show the narray
#
p nmap.na


jib:~/eg/ruby/na_str > ruby a.rb
NArray(ref).int(3,4):
[ [ 0, 0, 0 ],
[ 0, 0, 0 ],
[ 0, 0, 0 ],
[ 1151439012, 1151439012, 1151439012 ] ]

jib:~/eg/ruby/na_str > ruby a.rb
NArray(ref).int(3,4):
[ [ 1151439012, 1151439012, 1151439012 ],
[ 0, 0, 0 ],
[ 0, 0, 0 ],
[ 1151439014, 1151439014, 1151439014 ] ]


SPEED

jib:~/eg/ruby/na_str > cat a.rb
#
# reference impl installed with na_str
#
require 'nmap'
#
# setup a narray grid containing 1 gb of ints
#
gb = 2 ** 30
mb = 2 ** 20
sizeof_int = [42].pack('i').size
gig_of_ints = gb / sizeof_int
nmap = NMap.int '1GB', gig_of_ints
#
# set about 1 million of the ints to 42
#
nmap.na[0 .. mb] = 42
#
# show that the data was written
#
p nmap.na[mb - 1]


jib:~/eg/ruby/na_str > time ruby a.rb
42

real 0m0.078s
user 0m0.020s
sys 0m0.020s


jib:~/eg/ruby/na_str > ls -ltar 1GB
-rw-rw-r-- 1 ahoward ahoward 1073741824 Jun 27 14:28 1GB




--
-a

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