Multiple subproviders

var ZeroClientProvider = require('web3-provider-engine/zero.js')
var Web3 = require('web3')
var lightwallet = require('eth-lightwallet')

var interval = 4000

var keyStore = lightwallet.keystore

keyStore.createVault({
  password: "abc",
  seedPhrase: "method magic hair item student maple glide clown onion expire fuel sport", // Optionally provide a 12-word seed phrase
  // salt: fixture.salt,     // Optionally provide a salt.
  // A unique salt will be generated otherwise.
  // hdPathString: hdPath    // Optional custom HD Path String
}, function(err, ks) {

  console.log(err, ks)

  // Some methods will require providing the `pwDerivedKey`,
  // Allowing you to only decrypt private keys on an as-needed basis.
  // You can generate that value with this convenient method:
  ks.keyFromPassword("abc", function(err, pwDerivedKey) {
    if (err) throw err;

    // generate five new address/private key pairs
    // the corresponding private keys are also encrypted
    ks.generateNewAddress(pwDerivedKey, 5);
    var addr = ks.getAddresses();
    console.log(addr[0])

    ks.passwordProvider = function(callback) {
      callback(null, "abc");
    };

    var engines = [0, 1, 2, 3].map(i => new ZeroClientProvider({
      getAccounts: (callback) => callback(null, ks.getAddresses().map(a => '0x' + a)),
      signTransaction: (tx, callback) => {
        return ks.signTransaction(tx, callback)
      },
      rpcUrl: 'http://localhost:8545'
    }))

    var web3 = engines.map(e => new Web3(e))

    web3.forEach((w, i) => setTimeout(() => setInterval(() => w.eth.sendTransaction({
      from: addr[0],
      to: addr[1],
      value: i
    }, (err, h) => console.log("     ",i,"     ",(err || "none").toString().slice(0, 10), h)), 4*interval), interval * i))



  });
});