@sap/cds/libx/queue/JobExecutor.js

SAP Cloud Application Programming Model - CDS for Node.js

const PROCESSING = 'processing'
const LOCKED = 'locked'
const QUEUED = 'queued'
const CALLBACKS = 'callbacks'

module.exports = class JobExecutor {
  constructor() {
    statify(this)
  }

  run({ target, tenant, after }, cb) {
    const exec = () => {
      const processingState = this._get_state(PROCESSING, { target, tenant })
      if (processingState === LOCKED) {
        this._set_state(PROCESSING, QUEUED, { target, tenant })
        return
      }
      if (processingState === QUEUED) return
      if (!processingState) this._set_state(PROCESSING, LOCKED, { target, tenant })
      return cb()
    }
    setTimeout(exec, after || 0).unref()
  }

  end({ target, tenant }, cb) {
    const processingState = this._get_state(PROCESSING, { target, tenant })
    this._set_state(PROCESSING, undefined, { target, tenant })
    if (processingState === QUEUED) {
      setTimeout(cb, 0).unref()
    } else {
      // Truly done - call all done callbacks
      const callbacks = this._clearCallbacks({ target, tenant })
      if (callbacks) callbacks.forEach(callback => callback())
    }
  }

  addCallback({ target, tenant }, callback) {
    const existing = this._get_state(CALLBACKS, { target, tenant }) || []
    if (!existing.includes(callback)) {
      existing.push(callback)
      this._set_state(CALLBACKS, existing, { target, tenant })
    }
  }

  _clearCallbacks({ target, tenant }) {
    const callbacks = this._get_state(CALLBACKS, { target, tenant })
    this._set_state(CALLBACKS, undefined, { target, tenant })
    return callbacks
  }
}

const statify = that => {
  if (that._states) return

  that._states = new Map()

  that._set_state = (prop, state, { target, tenant }) => {
    const statesSrv = that._states.get(target)
    if (!statesSrv) {
      const newStatesSrv = new Map()
      newStatesSrv.set(tenant, { [prop]: state })
      that._states.set(target, newStatesSrv)
      return state
    }
    const obj = statesSrv.get(tenant)
    if (!obj) {
      statesSrv.set(tenant, { [prop]: state })
      return state
    }
    obj[prop] = state
    return state
  }

  that._get_state = (prop, { target, tenant }) => {
    const statesSrv = that._states.get(target)
    if (!statesSrv) return
    const obj = statesSrv.get(tenant)
    return obj && obj[prop]
  }
}