mongodb-lock

A really light-weight way to get distributed locks with a nice API if you're already using MongoDB.

Synopsis

Create a connection to your MongoDB database, and use it to create a lock object:

var mongodb = require('mongodb')
var mongoDbLock = require('mongodb-lock')

var con = 'mongodb://localhost:27017/test'

mongodb.MongoClient.connect(con, function(err, db) {
  // supply the database, the collection to use and the lock name
  var lock = mongoDbLock(db, 'locks', 'database-backup')
})

Now, acquire the lock:

lock.acquire(function(err, code) {
  if (err) {
    return console.error(code)
  }

  if ( code ) {
    // lock was acquired
    console.log('code=' + code)
  }
  else {
    // lock was not acquired
  }
})

Once you have a lock, you have a 30 second timeout until the lock is released. You can release it earlier by supplying the code:

lock.release(code, function(err, ok) {
  if (err) {
    return console.error(err)
  }

  if (ok) {
    console.log('Lock released ok')
  }
  else {
    console.log("Lock was not released, perhaps it's already been released or timed out")
  }
})

MongoDB Indexes

You should make sure any indexes have been added to the collection to make the queries faster:

lock.ensureIndexes(function(err) {
  if (err) {
    return console.error(err)
  }
  // all ok
})

Multiple Locks

Multiple locks can use the same collection and operate quite independently:

var dbBackupLock = mongoDbLock(db, 'locks', 'database-backup')
var hourlyStats = mongoDbLock(db, 'locks', 'hourly-stats')
var sendInvoices = mongoDbLock(db, 'locks', 'send-invoices')

Options

Currently there is only the option of the timeout. Currently the default is 30 seconds, but you can change it (in milliseconds):

// lock for 60 seconds
var uploadFiles = mongoDbLock(db, 'locks', 'upload-files', { timeout : 60 * 1000})

uploadFiles.lock(function(err, code) {
  // locked for 60s
})

0.2.0 (2015-04-17)

• [FIX] made sure that a 2nd .release() doesn't return ok (ie. it didn't do anything)

0.1.0 (2015-04-17)

• [NEW] added ability to add indexes to MongoDB
• [NEW] added lock()
• [NEW] added release()

Author

Written by Andrew Chilton - Twitter.

License

MIT - http://chilts.mit-license.org/2014/

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