graceful-fs.js

// Monkey-patching the fs module.
// It's ugly, but there is simply no other way to do this.
var fs = module.exports = require('fs')

var assert = require('assert')

// fix up some busted stuff, mostly on windows and old nodes
require('./polyfills.js')

// The EMFILE enqueuing stuff

var util = require('util')

function noop () {}

var debug = noop
if (util.debuglog)
  debug = util.debuglog('gfs')
else if (/\bgfs\b/i.test(process.env.NODE_DEBUG || ''))
  debug = function() {
    var m = util.format.apply(util, arguments)
    m = 'GFS: ' + m.split(/\n/).join('\nGFS: ')
    console.error(m)
  }

if (/\bgfs\b/i.test(process.env.NODE_DEBUG || '')) {
  process.on('exit', function() {
    debug('fds', fds)
    debug(queue)
    assert.equal(queue.length, 0)
  })
}


var originalOpen = fs.open
fs.open = open

function open(path, flags, mode, cb) {
  if (typeof mode === "function") cb = mode, mode = null
  if (typeof cb !== "function") cb = noop
  new OpenReq(path, flags, mode, cb)
}

function OpenReq(path, flags, mode, cb) {
  this.path = path
  this.flags = flags
  this.mode = mode
  this.cb = cb
  Req.call(this)
}

util.inherits(OpenReq, Req)

OpenReq.prototype.process = function() {
  originalOpen.call(fs, this.path, this.flags, this.mode, this.done)
}

var fds = {}
OpenReq.prototype.done = function(er, fd) {
  debug('open done', er, fd)
  if (fd)
    fds['fd' + fd] = this.path
  Req.prototype.done.call(this, er, fd)
}


var originalReaddir = fs.readdir
fs.readdir = readdir

function readdir(path, cb) {
  if (typeof cb !== "function") cb = noop
  new ReaddirReq(path, cb)
}

function ReaddirReq(path, cb) {
  this.path = path
  this.cb = cb
  Req.call(this)
}

util.inherits(ReaddirReq, Req)

ReaddirReq.prototype.process = function() {
  originalReaddir.call(fs, this.path, this.done)
}

ReaddirReq.prototype.done = function(er, files) {
  if (files && files.sort)
    files = files.sort()
  Req.prototype.done.call(this, er, files)
  onclose()
}


var originalClose = fs.close
fs.close = close

function close (fd, cb) {
  debug('close', fd)
  if (typeof cb !== "function") cb = noop
  delete fds['fd' + fd]
  originalClose.call(fs, fd, function(er) {
    onclose()
    cb(er)
  })
}


var originalCloseSync = fs.closeSync
fs.closeSync = closeSync

function closeSync (fd) {
  try {
    return originalCloseSync(fd)
  } finally {
    onclose()
  }
}


// Req class
function Req () {
  // start processing
  this.done = this.done.bind(this)
  this.failures = 0
  this.process()
}

Req.prototype.done = function (er, result) {
  var tryAgain = false
  if (er) {
    var code = er.code
    var tryAgain = code === "EMFILE"
    if (process.platform === "win32")
      tryAgain = tryAgain || code === "OK"
  }

  if (tryAgain) {
    this.failures ++
    enqueue(this)
  } else {
    var cb = this.cb
    cb(er, result)
  }
}

var queue = []

function enqueue(req) {
  queue.push(req)
  debug('enqueue %d %s', queue.length, req.constructor.name, req)
}

function onclose() {
  var req = queue.shift()
  if (req) {
    debug('process', req.constructor.name, req)
    req.process()
  }
}