Index: node_modules/tar/lib/path-reservations.js
===================================================================
--- node_modules/tar/lib/path-reservations.js	(revision 81bc7da776d8cda42939ef4ab350c88d13b4941f)
+++ node_modules/tar/lib/path-reservations.js	(revision 81bc7da776d8cda42939ef4ab350c88d13b4941f)
@@ -0,0 +1,156 @@
+// 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')
+const normalize = require('./normalize-unicode.js')
+const stripSlashes = require('./strip-trailing-slashes.js')
+const { join } = require('path')
+
+const platform = process.env.TESTING_TAR_FAKE_PLATFORM || process.platform
+const isWindows = platform === 'win32'
+
+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
+  // '/a/b/c/d' -> ['/', '/a', '/a/b', '/a/b/c', '/a/b/c/d']
+  const getDirs = path => {
+    const dirs = path.split('/').slice(0, -1).reduce((set, path) => {
+      if (set.length) {
+        path = join(set[set.length - 1], path)
+      }
+      set.push(path || '/')
+      return set
+    }, [])
+    return dirs
+  }
+
+  // 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) => {
+    // collide on matches across case and unicode normalization
+    // On windows, thanks to the magic of 8.3 shortnames, it is fundamentally
+    // impossible to determine whether two paths refer to the same thing on
+    // disk, without asking the kernel for a shortname.
+    // So, we just pretend that every path matches every other path here,
+    // effectively removing all parallelization on windows.
+    paths = isWindows ? ['win32 parallelization disabled'] : paths.map(p => {
+      // don't need normPath, because we skip this entirely for windows
+      return stripSlashes(join(normalize(p))).toLowerCase()
+    })
+
+    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 }
+}