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