parchan

Order preserving array-like channel. Used to execute functions in parallel with concurrency and stream-like functionality. Think batch or async.queue, but streaming!

var parchan = require('parchan')

co(function* () {
  var ch = parchan()
  // only two file descriptors open at a time
  ch.concurrency = 2

  var files = [
    '1.txt',
    '2.txt',
    '3.txt',
    '4.txt',
    '5.txt',
    '6.txt',
  ]

  // create and push the functions
  files.forEach(function (filename) {
    ch.push(function (done) {
      fs.readFile(filename, 'utf8', done)
    })
  })

  while (ch.readable) {
    // write each file to stdout in order
    process.stdout.write(yield* ch.read())
  }

  // exit the process
  process.exit()
})

or concatenate them all with:

var results = yield* ch.flush()
var string = results.join('')

This is very similar to other libraries like batch except:

• You can push functions and pull data while the callbacks are in progress
• You don't have to wait until all the callbacks are finished for you to start reading data
• You don't have to wait until you define all or even any callbacks to begin reading
• Data will always be returned in the correct order

The general use-case is concatenating files (as the example above).

API

var ch = archan([options])

• concurrency - maximum number of concurrent callbacks
• discard - discard the results of the callbacks. Will only return errors, if any, if true.
• closed or open - by default, the channel is closed, meaning yield* ch.flush() will flush only the remaining callbacks. If opened, yield* ch.flush() will not yield until the channel is closed.

ch.push(fn)

Push a thunk to the channel.

var result = yield* ch.read()

Pull the next value in the channel. This waits for the next result in the channel indefinitely whether or not the channel is closed.

If an error was thrown, this function will throw that error, and no more additional callbacks will be executed. To continue executing callbacks, just .read() again.

If this.out === true, errors will be thrown in the correct order. Otherwise, errors will be thrown ASAP.

var results = yield* ch.flush()

Waits until all the pending callbacks are completed. Unless you are discarding data, all the results of the callbacks will be returned as results.

ch.queue

Number of results waiting to be read.

ch.readable

If you can yield* ch.read(). Otherwise, a yield* ch.read() call may never be yielded.

ch.closed

Whether the channel is closed. true by default.

License

The MIT License (MIT)

Copyright (c) 2014 Jonathan Ong [e-mail]

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.