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!

``js
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:

`js
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

$3

- 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.

$3

Push a thunk to the channel.

$3

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.

$3

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

$3

Number of results waiting to be read.

$3

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

$3

Whether the channel is closed. true` by default.

License

The MIT License (MIT)

Copyright (c) 2014 Jonathan Ong me@jongleberry.com

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.