git ssb

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const Actor = require('./actor.js')
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const Scheduler = require('./scheduler.js')
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module.exports = class Hypervisor {
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  /**
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   * The Hypervisor manages the container instances by instantiating them and
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   * destorying them when possible. It also facilitates localating Containers
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   * @param {Tree} tree - a [radix tree](https://github.com/dfinity/js-dfinity-radix-tree) to store the state
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   */
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  constructor (tree, nonce = 0) {
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    this.tree = tree
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    this.scheduler = new Scheduler()
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    this._containerTypes = {}
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    this.nonce = nonce
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  }
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  /**
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   * sends a message
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   * @param {Object} cap - the capabilitly used to send the message
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   * @param {Object} message - the [message](https://github.com/primea/js-primea-message) to send
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   * @returns {Promise} a promise that resolves once the receiving container is loaded
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   */
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  async send (message) {
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    const id = message.funcRef.destId
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    const instance = await this.getActor(id)
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    instance.queue(message)
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  }
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  // loads an instance of a container from the state
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  async _loadActor (id) {
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    const state = await this.tree.getSubTree(id)
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    const {type, nonce} = Actor.deserializeMetaData(state.root['/'][3])
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    const container = this._containerTypes[type]
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    // create a new actor instance
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    const actor = new Actor({
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      hypervisor: this,
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      state,
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      container,
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      id,
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      nonce,
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      type
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    })
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    await actor.startup()
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    // save the newly created instance
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    this.scheduler.update(actor)
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    return actor
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  }
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  /**
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   * gets an existsing actor
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   * @param {string} id - the actor's ID
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   * @returns {Promise}
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   */
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  async getActor (id) {
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    let actor = this.scheduler.getInstance(id)
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    if (!actor) {
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      const resolve = this.scheduler.lock(id)
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      actor = await this._loadActor(id)
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      resolve(actor)
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    }
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    return actor
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  }
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  /**
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   * creates an instance of an Actor
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   * @param {Integer} type - the type id for the container
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   * @param {Object} message - an intial [message](https://github.com/primea/js-primea-message) to send newly created actor
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   * @param {Object} id - the id for the actor
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   */
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  async createActor (type, code, id = {nonce: this.nonce++, parent: null}) {
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    const encoded = encodedID(id)
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    const idHash = await this._getHashFromObj(encoded)
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    const metaData = Actor.serializeMetaData(type)
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    // save the container in the state
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    this.tree.set(idHash, metaData)
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    const Container = this._containerTypes[type]
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    await Container.validate(code)
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    const module = await Container.compile(code)
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    return {
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      id: idHash,
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      exports: Container.exports(module, idHash)
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    }
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  }
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  // get a hash from a POJO
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  _getHashFromObj (obj) {
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    return this.tree.constructor.getMerkleLink(obj)
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  }
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  /**
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   * creates a state root starting from a given container and a given number of
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   * ticks
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   * @param {Number} ticks the number of ticks at which to create the state root
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   * @returns {Promise}
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   */
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  async createStateRoot (ticks = Infinity) {
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    await this.scheduler.wait(ticks)
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    return this.tree.flush()
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  }
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  /**
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   * regirsters a container with the hypervisor
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   * @param {Class} Constructor - a Class for instantiating the container
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   * @param {*} args - any args that the contructor takes
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   * @param {Integer} typeId - the container's type identification ID
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   */
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  registerContainer (Constructor) {
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    this._containerTypes[Constructor.typeId] = Constructor
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  }
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}
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function encodedID (id) {
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  const nonce = Buffer.from([id.nonce])
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  if (id.parent) {
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    return Buffer.concat([nonce, id.parent])
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  } else {
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    return nonce
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  }
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}
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