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amnesia

Amnesia

Easy memory sharing between machines and/or processes for Node.js

  • A single variable (property) is shared between machines and/or processes
  • When this variable value changes, it is updated on all other machines/processes
  • Supported value types are JSON, String, Boolean and Number
  • Sharing is done using a TCP socket
  • Extremely simple and small. No other module dependency

Disclaimer:

  • No guarantees of concurrent writes, last one stands
  • No persistence. On restarts, it'll sync with other peers and get the most updated value
  • It's actually copying data, not strictly sharing the same memory allocation

Install

npm install amnesia

Usage

Use like any JavaScript object. The shared value is on the "data" property

var mem = require('amnesia');
mem.conf = [/* your configuration, see example below */];
mem.data = 1; // mem.data variable in all machines will have their value set to 1 
 

When value changes

mem.on('change', function(oldValue, newValue, remoteUpdate) {
    console.log('Value changed from', oldValue, 'to', newValue,
        (remoteUpdate ? 'remotely' : 'locally') );
    // remoteUpdate shows if the new value came from another machine (set remotely) 
})

See what is happening/debug

mem.on('log', function(msg) {
    console.log(msg);
})

When it was last updated

console.log(mem.updated);

Configuration

Copy conf.json to your application directory and edit/add your ips/ports

mem.conf = require('./conf');

OR add it directly to your code

mem.conf = [
    {
        "host" : "10.0.1.2",
        "port" : 7777
    },
    {
        "host" : "10.0.1.2",
        "port" : 8888
    },
    {
        "host" : "10.0.1.6",
        "port" : 8888
    }
]

If you'll share on the same machine with different processes, duplicate the ip with different ports

All machines should have the same configuration with the current machine's ip and its peers.

How it works

It uses the Object.defineProperty to add a custom setter and getter to the data property on the mem (amnesia) object.

When a value is set (i.e. mem.data = 1) the custom setter is called.

The custom setter sets the value to the local variable and also write its value to the TCP socket for each other peer.

Other peers receive the new value and set them locally to their mem.data. The 'change' event triggers.

When a new process/machine starts (or restarts), it gets the most updated value from its peers (sync request).

Interactive example

On machine 1:

node
> var mem = require('amnesia')
> mem.conf = require('./conf')
> mem.data = { jsontest : 123 } // <-- set to some json 
{ jsontest: 123 }
>

Then, on machine 2:

node
> var mem = require('amnesia')
> mem.conf = require('./conf') // <-- after adding config, a SYNC happens 
> mem.data // <-- value for mem.data is already set 
{ jsontest: 123 }
> mem.data = { jsontest: 456 } // <-- set a new value 
>

Back to machine 1:

> mem.data // <-- new value already on machine 1 
{ jsontest: 456 }
>

License

Licensed under the MIT license.