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mmap utilities for nodejs

mmap(2) / madvise(2) / msync(2) / mincore(2) for nodejs.

NOTE: this is a fork of https://github.com/ozra/mmap-io as that repo is unmaintained.

Installation

npm

$ npm install mmap-utils

git

$ git clone https://github.com/ipinfo/mmap-utils.git
$ cd mmap-utils
$ npm install
$ npm build

Usage

Note: All code in examples are in LiveScript

# Following code is plastic fruit; not t[ae]sted...

mmap = require "mmap-utils"
fs = require "fs"

some-file = "./foo.bar"

fd = fs.open-sync some-file, "r"
fd-w = fs.open-sync some-file, "r+"

# In the following comments:
# - `[blah]` denotes optional argument
# - `foo = x` denotes default value for argument

size = fs.fstat-sync(fd).size
rx-prot = mmap.PROT_READ .|. mmap.PROT_EXECUTE
priv = mmap.MAP_SHARED

# map( size, protection, privacy, fd [, offset = 0 [, advise = 0]] ) -> Buffer
buffer = mmap.map size, rx-prot, priv, fd
buffer2 = mmap.map size, mmap.PROT_READ, priv, fd, 0, mmap.MADV_SEQUENTIAL
w-buffer = mmap.map size, mmap.PROT_WRITE, priv, fd-w

# advise( buffer, advise ) -> void
# advise( buffer, offset, length, advise ) -> void
mmap.advise w-buffer, mmap.MADV_RANDOM

# sync( buffer ) -> void
# sync( buffer, offset, length ) -> void
# sync( buffer, is-blocking-sync[, do-page-invalidation = false] ) -> void
# sync( buffer, offset = 0, length = buffer.length [, is-blocking-sync = false [, do-page-invalidation = false]] ) -> void

mmap.sync w-buffer
mmap.sync w-buffer, true
mmap.sync w-buffer, 0, size
mmap.sync w-buffer, 0, size, true
mmap.sync w-buffer, 0, size, true, false

# incore( buffer ) -> [ unmapped-pages Int, mapped-pages Int ]
core-stats = mmap.incore buffer

Tests

$ npm run test

Misc

  • Checkout man pages mmap(2), madvise(2), msync(2), mincore(2) for more detailed intel.
  • The mappings are automatically unmapped when the buffer is garbage collected.
  • Write-mappings need the fd to be opened with "r+", or you'll get a permission error (13).
  • If you make a read-only mapping and then ignorantly set a value in the buffer, all hell previously unknown to a JS'er breaks loose (segmentation fault). It is possible to write some devilous code to intercept the SIGSEGV and throw an exception, but let's not do that!
  • Offset, and in some cases length needs to be a multiple of PAGESIZE (which commonly is 4096)
  • Huge pages are only supported for anonymous / private mappings (well, in Linux), so I didn't throw in flags for that since I found no use.
  • As Ben Noordhuis previously has stated: Supplying hint for a fixed virtual memory adress is kinda moot point in JS, so not supported.