git ssb

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const Buffer = require('safe-buffer').Buffer
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const binarySearchInsert = require('binary-search-insert')
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// decides which message to go first
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function messageArbiter (messageA, messageB) {
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  // order by number of ticks if messages have different number of ticks
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  if (messageA._fromTicks !== messageB._fromTicks) {
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    return messageA._fromTicks > messageB._fromTicks
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  } else {
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    // sender id
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    return Buffer.compare(messageA._fromId, messageB._fromId)
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  }
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}
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module.exports = class Inbox {
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  /**
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   * The inbox manages and sorts incoming messages and provides functions
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   * to wait on messages
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   * @param {Object} opts
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   * @param {Object} opts.state
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   * @param {Object} opts.hypervisor
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   */
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  constructor (opts) {
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    this.actor = opts.actor
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    this.hypervisor = opts.hypervisor
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    this._queue = []
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    this._waitingTagsQueue = []
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    this._oldestMessagePromise = new Promise((resolve, reject) => {
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      this._oldestMessageResolve = resolve
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    })
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  }
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  /**
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   * queues a message
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   * @param {Message} message
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   */
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  queue (message) {
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    this._queueMessage(message)
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    const oldestMessage = this._getOldestMessage()
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    if (oldestMessage === message) {
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      this._oldestMessageResolve(message)
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      this._oldestMessagePromise = new Promise((resolve, reject) => {
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        this._oldestMessageResolve = resolve
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      })
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    }
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  }
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  /**
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   * Waits for a message sent with a capablitly that has one of the given tags
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   * @param {Array<*>} tags
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   * @param {Integer} timeout
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   * @returns {Promise}
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   */
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  async nextTaggedMessage (tags, timeout) {
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    if (this._waitingTags) {
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      throw new Error('already waiting on tags')
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    }
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    this._waitingTags = new Set(tags)
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    this._queue = this._queue.filter(message => !this._queueTaggedMessage(message))
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    // todo: add saturation test
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    const message = await this.nextMessage(timeout)
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    delete this._waitingTags
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    this._waitingTagsQueue.forEach(message => this._queueMessage(message))
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    this._waitingTagsQueue = []
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    return message
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  }
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  /**
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   * Waits for the the next message if any
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   * @param {Integer} timeout
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   * @returns {Promise}
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   */
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  nextMessage (timeout) {
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    if (!this._gettingNextMessage) {
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      this._gettingNextMessage = this._nextMessage(timeout)
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    }
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    return this._gettingNextMessage
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  }
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  async _nextMessage (timeout = 0) {
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    await Promise.all([...this.actor._sending.values()])
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    let message = this._getOldestMessage()
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    if (message === undefined && timeout === 0) {
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      return
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    }
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    timeout += this.actor.ticks
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    let oldestTime = this.hypervisor.scheduler.leastNumberOfTicks(this.actor.id)
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    while (true) {
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      if (message) {
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        // if the message we recived had more ticks then we currently have then
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        // update our ticks to it, since we jumped forward in time
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        if (message._fromTicks > this.actor.ticks) {
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          this.actor.ticks = message._fromTicks
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          this.hypervisor.scheduler.update(this.actor)
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        }
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        // if there is a message that is "older" then the timeout, the lower
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        // the timeout to the oldest message
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        if (message._fromTicks < timeout) {
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          timeout = message._fromTicks
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        }
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      }
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      // if all actors are "older" then the time out then stop waiting for messages
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      // since we konw that we can not receive one
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      if (oldestTime >= timeout) {
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        break
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      }
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      await Promise.race([
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        this.hypervisor.scheduler.wait(timeout, this.actor.id).then(() => {
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          message = this._getOldestMessage()
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        }),
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        this._olderMessage(message).then(m => {
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          message = m
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        })
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      ])
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      oldestTime = this.hypervisor.scheduler.leastNumberOfTicks(this.actor.id)
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    }
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    this._gettingNextMessage = false
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    return this._deQueueMessage()
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  }
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  // returns a promise that resolve when a message older then the given message
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  // is recived
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  _olderMessage (message) {
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    return this._oldestMessagePromise
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  }
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  _getOldestMessage () {
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    if (this._waitingTags) {
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      return this._waitingTagsQueue[0]
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    } else {
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      return this._queue[0]
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    }
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  }
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  _deQueueMessage () {
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    if (this._waitingTags) {
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      return this._waitingTagsQueue.shift()
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    } else {
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      return this._queue.shift()
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    }
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  }
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  _queueMessage (message) {
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    if (!(this._waitingTags && this._queueTaggedMessage(message))) {
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      binarySearchInsert(this._queue, messageArbiter, message)
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    }
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  }
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  _queueTaggedMessage (message) {
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    if (this._waitingTags.has(message.tag)) {
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      this._waitingTags.delete(message.tag)
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      binarySearchInsert(this._waitingTagsQueue, messageArbiter, message)
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      return true
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    } else {
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      return false
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    }
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  }
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}
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