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multiqueue.js
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multiqueue.js
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const Promise = require('any-promise')
const co = require('co').wrap
const promisify = require('pify')
const collect = promisify(require('stream-collector'))
const clone = require('xtend')
const subdown = require('subleveldown')
const prefixer = require('sublevel-prefixer')
const pump = require('pump')
const through = require('through2')
const extend = require('xtend/mutable')
// const CombinedStream = require('combined-stream2')
const merge = require('merge2')
const omit = require('object.omit')
const AsyncEmitter = require('./async-emitter')
const implAutoincrement = require('./impl-autoincrement')
const implCustomSeq = require('./impl-custom-seq')
const {
hexint,
unhexint,
createPassThrough,
assert,
validateEncoding,
firstInStream,
getSublevelPrefix,
createKeyParserTransform,
pluckValuesTransform
} = require('./utils')
const SEPARATOR = '!'
const MIN_CHAR = '\x00'
const MAX_CHAR = '\xff'
const NAMESPACE = {
main: 'm',
checkpoint: 'c'
}
const FIRST_SEQ = 0
module.exports = function createQueues ({ db, separator=SEPARATOR, autoincrement=true }) {
const { valueEncoding } = db.options
const prefix = prefixer(separator)
const mainDB = subdown(db, NAMESPACE.main, { valueEncoding, separator })
const checkpointsDB = subdown(db, NAMESPACE.checkpoint, { valueEncoding: 'json' })
const getAsync = promisify(db.get.bind(db))
const batchAsync = promisify(db.batch.bind(db))
const delCheckpointAsync = promisify(checkpointsDB.del.bind(checkpointsDB))
const putCheckpointAsync = promisify(checkpointsDB.put.bind(checkpointsDB))
const queues = {}
const ee = new AsyncEmitter()
const tips = {}
const have = {}
const keyParser = createKeyParserTransform(parseKey)
function markHave ({ queue, seq }) {
if (!have[queue]) have[queue] = {}
have[queue][seq] = true
}
function clearHave ({ queue, seq }) {
if (have[queue] && have[queue][seq]) {
delete have[queue][seq]
return true
}
}
function getQueueKeyRange ({ queue }) {
const gt = getQueuePrefix(queue)
const lt = gt + MAX_CHAR
return { gt, lt }
}
const impl = (autoincrement ? implAutoincrement : implCustomSeq)({ createQueueStream })
function getQueue (identifier) {
if (!queues[identifier]) {
queues[identifier] = createQueue(identifier)
}
return queues[identifier]
}
/**
* the "tip" is the seq of the latest queued item excluding gaps
* e.g. if [0, 1, 2, 5, 6] are queued, the tip is 2
*/
const getQueueTip = co(function* ({ queue }) {
let tip = tips[queue]
if (typeof tip !== 'undefined') {
return tip
}
// the non-autoincrement implementation needs to know
// the seq of the last dequeued item
tip = yield impl.tip({
queue,
getCheckpoint: () => getQueueCheckpoint({ queue })
})
tip = typeof tip === 'undefined' ? FIRST_SEQ - 1 : tip
return tips[queue] = tip
})
const clearQueue = co(function* ({ queue }) {
yield Promise.all([
yield collect(pump(
mainDB.createReadStream(extend({
values: false
}, getQueueKeyRange({ queue }))),
through.obj(function (key, enc, cb) {
mainDB.del(key, cb)
})
)),
delCheckpointAsync(queue)
])
delete tips[queue]
})
function createQueue (queue) {
const sub = subdown(mainDB, queue, { valueEncoding, separator })
const batchEnqueueInternal = impl.batchEnqueuer({ db: sub, queue })
const promiseTip = getQueueTip({ queue })
let tip
const updateTip = co(function* ({ seq }) {
if (typeof tip === 'undefined') tip = yield promiseTip
let newTip = tip
if (tips[queue] + 1 === seq) {
clearHave({ queue, seq })
newTip = seq
} else {
markHave({ queue, seq })
}
while (clearHave({ queue, seq: newTip + 1 })) {
newTip++
}
if (newTip !== tip) {
tip = tips[queue] = newTip
ee.emitAsync('tip', { queue, tip })
}
return tip
})
const enqueue = co(function* ({ value, seq }) {
const results = yield batchEnqueue({
data: [{ value, seq }]
})
return results[0]
})
const batchEnqueue = co(function* ({ data }) {
data = data.slice()
if (!autoincrement) {
data.sort(sortAscendingBySeq)
}
const seqs = yield batchEnqueueInternal({ data })
if (seqs[0] === FIRST_SEQ) {
yield putCheckpointAsync(queue, FIRST_SEQ - 1)
}
let tip
for (let seq of seqs) {
tip = yield updateTip({ seq })
}
return data.map((item, i) => {
const { value } = item
const seq = seqs[i]
const key = getKey({ queue, seq })
const ret = { key, value, queue, tip, seq }
ee.emitAsync('enqueue', ret)
return ret
})
})
return {
getItemAtSeq: seq => getItemAtIndex({ queue, seq }),
queued: () => getQueued(queue),
enqueue,
dequeue: () => dequeue({ queue }),
batchEnqueue,
createReadStream: createQueueStream.bind(null, queue),
tip: () => getQueueTip({ queue }),
clear: () => clearQueue({ queue }),
checkpoint: () => getQueueCheckpoint({ queue })
}
}
function getItemAtIndex ({ queue, seq }) {
return getAsync(getKey({ queue, seq }))
}
function createQueueStream (queue, opts) {
opts = extend(getQueueKeyRange({ queue }), opts)
return createReadStream(opts)
}
function validateQueueName (queue) {
assert(typeof queue === 'string', 'expected string "queue"')
if (queue.indexOf(separator) !== -1) {
throw new Error('"queue" must not contain "separator"')
}
}
const enqueue = co(function* ({ value, queue, seq }) {
validateQueueName(queue)
if (!autoincrement) {
assert(typeof seq === 'number', 'expected "seq"')
}
validateEncoding({ value, encoding: valueEncoding })
yield getQueue(queue).enqueue({ value, seq })
})
const batchEnqueue = co(function* ({ queue, data }) {
validateQueueName(queue)
if (!autoincrement) {
assert(data.every(data => typeof data.seq === 'number'), 'expected every item to have a "seq"')
}
data.forEach(data => validateEncoding({ value: data.value, encoding: valueEncoding }))
yield getQueue(queue).batchEnqueue({ queue, data })
})
const dequeue = co(function* ({ queue }) {
assert(typeof queue === 'string', 'expected string "queue"')
const checkpoint = yield getQueueCheckpoint({ queue })
const seq = typeof checkpoint === 'undefined' ? FIRST_SEQ : checkpoint + 1
const batch = [
{ type: 'del', key: getKey({ queue, seq }) },
{ type: 'put', key: getCheckpointKey(queue), value: seq }
]
yield batchAsync(batch)
ee.emitAsync('dequeue', { queue, seq })
})
/**
* Get the seq of the last dequeued item
*/
function getQueueCheckpoint ({ queue }) {
return new Promise(resolve => {
checkpointsDB.get(queue, function (err, result) {
resolve(err ? FIRST_SEQ - 1 : result)
})
})
}
function createReadStream (opts={}) {
if (opts.queue) {
return createQueueStream(opts.queue, omit(opts, 'queue'))
}
const old = mainDB.createReadStream(extend({
keys: true,
values: true,
gt: separator
}, opts))
const merged = merge(old, { end: !opts.live })
if (opts.live) {
const live = createPassThrough()
ee.on('enqueue', onEnqueue)
merged.add(live)
merged.on('queueDrain', () => {
ee.removeListener('enqueue', onEnqueue)
})
function onEnqueue (data) {
live.write(data)
}
}
return pump(merged, keyParser(opts))
}
function getQueues () {
return collect(checkpointsDB.createReadStream({ values: false }))
}
function getCheckpointKey (queue) {
return prefix(NAMESPACE.checkpoint, queue)
}
function getKey ({ queue, seq }) {
// BAD as it assumes knowledge of changes-feed internals
return prefix(NAMESPACE.main, prefix(queue, hexint(seq)))
}
function getQueuePrefix (queue) {
return prefix(queue, '')
}
function parseKey (key) {
const parts = key.split(separator)
const seq = unhexint(parts.pop())
const queue = parts.pop()
return { queue, seq }
}
function getQueued (queue, opts) {
if (typeof queue === 'object') {
opts = queue
queue = null
}
const source = queue ? createQueueStream(queue, opts) : createReadStream(opts)
return collect(source)
}
return extend(ee, {
firstSeq: FIRST_SEQ,
autoincrement,
queue: getQueue,
batchEnqueue,
enqueue,
dequeue,
createReadStream,
queues: getQueues,
checkpoint: getQueueCheckpoint,
queued: getQueued
})
}
function sortAscendingBySeq (a, b) {
return a.seq - b.seq
}