lib,test: deprecate _linklist

Deprecate _linklist and add test to confirm internal linklist and
public _linklist are the same.

lib/_linklist.js

@@ -1,57 +1,6 @@
 'use strict';
 
-function init(list) {
-  list._idleNext = list;
-  list._idlePrev = list;
-}
-exports.init = init;
+const msg = require('internal/util').printDeprecationMessage;
 
-
-// show the most idle item
-function peek(list) {
-  if (list._idlePrev == list) return null;
-  return list._idlePrev;
-}
-exports.peek = peek;
-
-
-// remove the most idle item from the list
-function shift(list) {
-  var first = list._idlePrev;
-  remove(first);
-  return first;
-}
-exports.shift = shift;
-
-
-// remove a item from its list
-function remove(item) {
-  if (item._idleNext) {
-    item._idleNext._idlePrev = item._idlePrev;
-  }
-
-  if (item._idlePrev) {
-    item._idlePrev._idleNext = item._idleNext;
-  }
-
-  item._idleNext = null;
-  item._idlePrev = null;
-}
-exports.remove = remove;
-
-
-// remove a item from its list and place at the end.
-function append(list, item) {
-  remove(item);
-  item._idleNext = list._idleNext;
-  list._idleNext._idlePrev = item;
-  item._idlePrev = list;
-  list._idleNext = item;
-}
-exports.append = append;
-
-
-function isEmpty(list) {
-  return list._idleNext === list;
-}
-exports.isEmpty = isEmpty;
+module.exports = require('internal/linkedlist');
+msg('_linklist module is deprecated. Please use a userland alternative.');

lib/internal/linkedlist.js

@@ -0,0 +1,57 @@
+'use strict';
+
+function init(list) {
+  list._idleNext = list;
+  list._idlePrev = list;
+}
+exports.init = init;
+
+
+// show the most idle item
+function peek(list) {
+  if (list._idlePrev == list) return null;
+  return list._idlePrev;
+}
+exports.peek = peek;
+
+
+// remove the most idle item from the list
+function shift(list) {
+  var first = list._idlePrev;
+  remove(first);
+  return first;
+}
+exports.shift = shift;
+
+
+// remove a item from its list
+function remove(item) {
+  if (item._idleNext) {
+    item._idleNext._idlePrev = item._idlePrev;
+  }
+
+  if (item._idlePrev) {
+    item._idlePrev._idleNext = item._idleNext;
+  }
+
+  item._idleNext = null;
+  item._idlePrev = null;
+}
+exports.remove = remove;
+
+
+// remove a item from its list and place at the end.
+function append(list, item) {
+  remove(item);
+  item._idleNext = list._idleNext;
+  list._idleNext._idlePrev = item;
+  item._idlePrev = list;
+  list._idleNext = item;
+}
+exports.append = append;
+
+
+function isEmpty(list) {
+  return list._idleNext === list;
+}
+exports.isEmpty = isEmpty;

lib/timers.js

@@ -1,7 +1,7 @@
 'use strict';
 
 const Timer = process.binding('timer_wrap').Timer;
-const L = require('_linklist');
+const L = require('internal/linkedlist');
 const assert = require('assert').ok;
 const util = require('util');
 const debug = util.debuglog('timer');

node.gyp

@@ -17,7 +17,6 @@
       'src/node.js',
       'lib/_debug_agent.js',
       'lib/_debugger.js',
-      'lib/_linklist.js',
       'lib/assert.js',
       'lib/buffer.js',
       'lib/child_process.js',
@@ -39,6 +38,7 @@
       'lib/_http_outgoing.js',
       'lib/_http_server.js',
       'lib/https.js',
+      'lib/_linklist.js',
       'lib/module.js',
       'lib/net.js',
       'lib/os.js',
@@ -70,9 +70,10 @@
       'lib/zlib.js',
       'lib/internal/child_process.js',
       'lib/internal/freelist.js',
+      'lib/internal/linkedlist.js',
       'lib/internal/module.js',
-      'lib/internal/socket_list.js',
       'lib/internal/repl.js',
+      'lib/internal/socket_list.js',
       'lib/internal/util.js',
       'lib/internal/streams/lazy_transform.js',
     ],

test/parallel/test-timers-linked-list.js

@@ -1,8 +1,13 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
-var L = require('_linklist');
 
+// Flags: --expose-internals
+
+const common = require('../common');
+const assert = require('assert');
+const L = require('_linklist');
+const internalL = require('internal/linkedlist');
+
+assert.strictEqual(L, internalL);
 
 var list = { name: 'list' };
 var A = { name: 'A' };