mongodb-lock

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

Version 1.0 !!!

Please note that the API has changed for v1.0 (compared to v0.4 and previously). This fits in with MongoDB Driver v3 and above.

Synopsis

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

const mongodb = require('mongodb')
const mongoDbLock = require('.')

const url = 'mongodb://localhost:27017/'
const dbName = 'test'
const colName = 'locks'
const lockName = 'database-backup'

mongodb.MongoClient.connect(url, { useNewUrlParser: true }, function(err, client) {
  const db = client.db(dbName)
  const col = db.collection(colName)

  // supply the collection to use and the lock name
  const lock = mongoDbLock(col, lockName)
  lock.ensureIndexes(function(err, result) {
    console.log('Ensured Index:', err, result)
  })

  // Your Program Here!

})

Now, acquire the lock:

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

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

  // lock was 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, (err, ok) => {
  if (err) {
    return console.error(err)
  }

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

  console.log('Lock released ok')
})

MongoDB Indexes

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

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

Multiple Locks

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

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

Options

Currently there are two options: timeout and removeExpired

timeout

Currently the default is 30 seconds, but you can change it (in milliseconds):

// lock for 60 seconds
const opts = { timeout : 60 * 1000 }

// create the lock object
const uploadFiles = mongoDbLock(db, 'locks', 'upload-files', opts)

// acquire the lock
uploadFiles.lock((err, code) => {
  // locked for 60s
})

removeExpired

Currently the default value is false.

When set to true this will remove expired lock records from MongoDB instead of modifying them.

// remove old locks from MongoDB
const opts = { removeExpired : true }

// create the lock object
const cleanUpCacheDirs = mongoDbLock(db, 'locks', 'clean-up-cache-dirs', opts)

// all old locks are now deleted, rather than just hanging around

Changelog

1.0.0 (2019-08-08)

• [FIX] made sure MongoDB Lock works with the MongoDB driver >v3
• Yay - v1.0.0!

0.4.0 (2017-03-07)

• Allow option so old locks are removed rather than updated (thanks Aiden Keating)

0.3.0 (2017-03-07)

• Support for the MongoDB Driver v2 (thanks Aiden Keating)
• Better ReadMe (thanks Marek)
• Better ReadMe (thanks Krasiyan Nedelchev)

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

$ npx chilts

   ╒════════════════════════════════════════════════════╕
   │                                                    │
   │   Andrew Chilton (Personal)                        │
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   │          Email : [email protected]             │
   │            Web : https://chilts.org                │
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   │                                                    │
   │   Apps Attic Ltd (My Company)                      │
   │   ---------------------------                      │
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   │          Email : [email protected]              │
   │            Web : https://appsattic.com             │
   │        Twitter : https://twitter.com/AppsAttic     │
   │         GitLab : https://gitlab.com/appsattic      │
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   │   Node.js / npm                                    │
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   │        Profile : https://www.npmjs.com/~chilts     │
   │           Card : $ npx chilts                      │
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License

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

(Ends)