Binary Semaphore: a mutex lock to run on Heroku

This simple Node server offers an infinite set of mutexes via HTTP API.

You acquire a lock by PUT request to /lock/:id/:nonce.

There id is the lock's identifier, and nonce is a random string you choose which is used to prevent certain conflicts.

You release the lock by DELETE to that same path.

All acquired locks expire automatically in a hard-coded number of seconds.

That should probably be configurable.

CORS is allowed for any domain origin.

We use this in https://github.com/mbrock/telegroam.

It's useful e.g. if you have several browser scripts that need to use some resource without conflicting with each other.

Note that you also need to enable Heroku Redis (the hobby free plan) on the created application.