126 lines
3.2 KiB
JavaScript
126 lines
3.2 KiB
JavaScript
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// A path exclusive reservation system
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// reserve([list, of, paths], fn)
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// When the fn is first in line for all its paths, it
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// is called with a cb that clears the reservation.
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//
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// Used by async unpack to avoid clobbering paths in use,
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// while still allowing maximal safe parallelization.
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const assert = require('assert')
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module.exports = () => {
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// path => [function or Set]
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// A Set object means a directory reservation
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// A fn is a direct reservation on that path
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const queues = new Map()
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// fn => {paths:[path,...], dirs:[path, ...]}
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const reservations = new Map()
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// return a set of parent dirs for a given path
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const { join } = require('path')
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const getDirs = path =>
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join(path).split(/[\\/]/).slice(0, -1).reduce((set, path) =>
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set.length ? set.concat(join(set[set.length - 1], path)) : [path], [])
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// functions currently running
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const running = new Set()
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// return the queues for each path the function cares about
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// fn => {paths, dirs}
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const getQueues = fn => {
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const res = reservations.get(fn)
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/* istanbul ignore if - unpossible */
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if (!res)
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throw new Error('function does not have any path reservations')
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return {
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paths: res.paths.map(path => queues.get(path)),
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dirs: [...res.dirs].map(path => queues.get(path)),
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}
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}
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// check if fn is first in line for all its paths, and is
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// included in the first set for all its dir queues
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const check = fn => {
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const {paths, dirs} = getQueues(fn)
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return paths.every(q => q[0] === fn) &&
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dirs.every(q => q[0] instanceof Set && q[0].has(fn))
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}
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// run the function if it's first in line and not already running
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const run = fn => {
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if (running.has(fn) || !check(fn))
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return false
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running.add(fn)
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fn(() => clear(fn))
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return true
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}
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const clear = fn => {
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if (!running.has(fn))
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return false
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const { paths, dirs } = reservations.get(fn)
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const next = new Set()
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paths.forEach(path => {
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const q = queues.get(path)
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assert.equal(q[0], fn)
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if (q.length === 1)
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queues.delete(path)
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else {
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q.shift()
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if (typeof q[0] === 'function')
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next.add(q[0])
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else
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q[0].forEach(fn => next.add(fn))
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}
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})
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dirs.forEach(dir => {
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const q = queues.get(dir)
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assert(q[0] instanceof Set)
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if (q[0].size === 1 && q.length === 1)
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queues.delete(dir)
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else if (q[0].size === 1) {
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q.shift()
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// must be a function or else the Set would've been reused
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next.add(q[0])
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} else
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q[0].delete(fn)
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})
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running.delete(fn)
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next.forEach(fn => run(fn))
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return true
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}
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const reserve = (paths, fn) => {
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const dirs = new Set(
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paths.map(path => getDirs(path)).reduce((a, b) => a.concat(b))
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)
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reservations.set(fn, {dirs, paths})
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paths.forEach(path => {
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const q = queues.get(path)
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if (!q)
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queues.set(path, [fn])
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else
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q.push(fn)
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})
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dirs.forEach(dir => {
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const q = queues.get(dir)
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if (!q)
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queues.set(dir, [new Set([fn])])
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else if (q[q.length - 1] instanceof Set)
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q[q.length - 1].add(fn)
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else
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q.push(new Set([fn]))
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})
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return run(fn)
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}
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return { check, reserve }
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}
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