git ssb

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const Kernel = require('./kernel.js')
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const Scheduler = require('./scheduler.js')
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const DFSchecker = require('./dfsChecker.js')
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const CreationService = require('./creationService.js')
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const CREATION_ID = 0
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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 {Graph} dag an instance of [ipfs.dag](https://github.com/ipfs/interface-ipfs-core/tree/master/API/dag#dag-api)
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   * @param {object} state - the starting state
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   */
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  constructor (tree) {
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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._nodesToCheck = new Set()
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    this.creationService = new CreationService({
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      hypervisor: this
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    })
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    this.scheduler.systemServices.set(CREATION_ID, this.creationService)
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    this.pinnedIds = new Set()
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  }
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  /**
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   * add a potaintail node in the state graph to check for garbage collection
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   * @param {string} id
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   */
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  addNodeToCheck (id) {
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    this._nodesToCheck.add(id)
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  }
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  /**
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   * given a port, this finds the corridsponeding endpoint port of the channel
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   * @param {object} port
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   * @returns {Promise}
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   */
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  async getDestPort (port) {
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    if (port.destPort) {
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      return port.destPort
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    } else {
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      const instance = await this.scheduler.getInstance(port.destId)
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      let containerState
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      if (instance) {
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        containerState = instance.state
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      } else {
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        let {value} = await this.tree.get(port.destId, true)
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        containerState = value
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      }
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      return this.tree.graph.get(containerState, `ports/${port.destName}`)
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    }
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  }
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  async send (port, message) {
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    const id = port.destId
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    if (id !== undefined) {
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      const instance = await this.getInstance(id)
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      return instance.queue(port, message)
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    } else {
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      // port is unbound
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      port.destPort.messages.push(message)
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    }
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  }
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  // loads an instance of a container from the state
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  async _loadInstance (id) {
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    const state = await this.tree.get(id, true)
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    const container = this._containerTypes[state.value.type]
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    // create a new kernel instance
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    const kernel = new Kernel({
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      hypervisor: this,
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      state: state.value,
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      node: state.node,
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      code: state.value.code,
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      container: container,
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      id: id
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    })
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    // save the newly created instance
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    this.scheduler.update(kernel)
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    return kernel
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  }
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  /**
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   * gets an existsing container instances
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   * @param {string} id - the containers ID
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   * @returns {Promise}
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   */
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  async getInstance (id) {
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    let instance = this.scheduler.getInstance(id)
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    if (instance) {
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      return instance
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    } else {
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      const resolve = this.scheduler.lock(id)
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      const instance = await this._loadInstance(id)
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      await instance.startup()
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      resolve(instance)
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      return instance
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    }
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  }
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  createChannel () {
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    const port1 = {
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      messages: []
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    }
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    const port2 = {
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      messages: [],
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      destPort: port1
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    }
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    port1.destPort = port2
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    return [port1, port2]
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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) {
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    await this.scheduler.wait(ticks)
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    const unlinked = await DFSchecker(this.tree, this._nodesToCheck, (id) => {
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      return this.pinnedIds.has(id)
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    })
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    for (const id of unlinked) {
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      await this.tree.delete(id)
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    }
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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 {interger} typeId - the container's type identification ID
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   */
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  registerContainer (Constructor, args, typeId = Constructor.typeId) {
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    this._containerTypes[typeId] = {
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      Constructor: Constructor,
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      args: args
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    }
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  }
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  pin (instance) {
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    this.pinnedIds.add(instance.id)
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  }
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}
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