107 lines
2.9 KiB
JavaScript
107 lines
2.9 KiB
JavaScript
'use strict'
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const { AbstractIterator } = require('abstract-level')
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const binding = require('./binding')
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const kContext = Symbol('context')
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const kCache = Symbol('cache')
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const kFinished = Symbol('finished')
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const kFirst = Symbol('first')
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const kPosition = Symbol('position')
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const kHandleNext = Symbol('handleNext')
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const kHandleNextv = Symbol('handleNextv')
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const kCallback = Symbol('callback')
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const empty = []
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// Does not implement _all() because the default implementation
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// of abstract-level falls back to nextv(1000) and using all()
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// on more entries than that probably isn't a realistic use case,
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// so it'll typically just make one nextv(1000) call and there's
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// no performance gain in overriding _all().
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class Iterator extends AbstractIterator {
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constructor (db, context, options) {
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super(db, options)
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this[kContext] = binding.iterator_init(context, options)
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this[kHandleNext] = this[kHandleNext].bind(this)
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this[kHandleNextv] = this[kHandleNextv].bind(this)
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this[kCallback] = null
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this[kFirst] = true
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this[kCache] = empty
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this[kFinished] = false
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this[kPosition] = 0
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}
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_seek (target, options) {
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this[kFirst] = true
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this[kCache] = empty
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this[kFinished] = false
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this[kPosition] = 0
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binding.iterator_seek(this[kContext], target)
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}
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_next (callback) {
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if (this[kPosition] < this[kCache].length) {
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const entry = this[kCache][this[kPosition]++]
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process.nextTick(callback, null, entry[0], entry[1])
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} else if (this[kFinished]) {
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process.nextTick(callback)
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} else {
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this[kCallback] = callback
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if (this[kFirst]) {
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// It's common to only want one entry initially or after a seek()
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this[kFirst] = false
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binding.iterator_nextv(this[kContext], 1, this[kHandleNext])
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} else {
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// Limit the size of the cache to prevent starving the event loop
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// while we're recursively calling process.nextTick().
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binding.iterator_nextv(this[kContext], 1000, this[kHandleNext])
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}
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}
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}
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[kHandleNext] (err, items, finished) {
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const callback = this[kCallback]
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if (err) return callback(err)
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this[kCache] = items
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this[kFinished] = finished
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this[kPosition] = 0
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this._next(callback)
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}
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_nextv (size, options, callback) {
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if (this[kFinished]) {
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process.nextTick(callback, null, [])
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} else {
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this[kCallback] = callback
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this[kFirst] = false
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binding.iterator_nextv(this[kContext], size, this[kHandleNextv])
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}
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}
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[kHandleNextv] (err, items, finished) {
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const callback = this[kCallback]
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if (err) return callback(err)
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this[kFinished] = finished
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callback(null, items)
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}
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_close (callback) {
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this[kCache] = empty
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this[kCallback] = null
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binding.iterator_close(this[kContext], callback)
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}
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// Undocumented, exposed for tests only
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get cached () {
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return this[kCache].length - this[kPosition]
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}
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}
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exports.Iterator = Iterator
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