[v8.x backport] lib: improve lazy requires

lib/dgram.js

@@ -24,6 +24,7 @@
 const assert = require('assert');
 const errors = require('internal/errors');
 const Buffer = require('buffer').Buffer;
+const dns = require('dns');
 const util = require('util');
 const EventEmitter = require('events');
 const setInitTriggerId = require('async_hooks').setInitTriggerId;
@@ -39,17 +40,13 @@ const BIND_STATE_UNBOUND = 0;
 const BIND_STATE_BINDING = 1;
 const BIND_STATE_BOUND = 2;
 
-// lazily loaded
+// Lazily loaded
 var cluster = null;
-var dns = null;
 
 const errnoException = util._errnoException;
 const exceptionWithHostPort = util._exceptionWithHostPort;
 
 function lookup(address, family, callback) {
-  if (!dns)
-    dns = require('dns');
-
   return dns.lookup(address, family, callback);
 }
 

lib/internal/errors.js

@@ -9,19 +9,9 @@
 const kCode = Symbol('code');
 const messages = new Map();
 
-var util;
-function lazyUtil() {
-  if (!util)
-    util = require('util');
-  return util;
-}
-
-var assert;
-function lazyAssert() {
-  if (!assert)
-    assert = require('assert');
-  return assert;
-}
+// Lazily loaded
+var assert = null;
+var util = null;
 
 function makeNodeError(Base) {
   return class NodeError extends Base {
@@ -45,13 +35,14 @@ class AssertionError extends Error {
     if (typeof options !== 'object' || options === null) {
       throw new exports.TypeError('ERR_INVALID_ARG_TYPE', 'options', 'object');
     }
-    const util = lazyUtil();
-    const message = options.message ||
-                    `${util.inspect(options.actual).slice(0, 128)} ` +
-                    `${options.operator} ` +
-                    util.inspect(options.expected).slice(0, 128);
+    if (options.message) {
+      super(options.message);
+    } else {
+      if (util === null) util = require('util');
+      super(`${util.inspect(options.actual).slice(0, 128)} ` +
+        `${options.operator} ${util.inspect(options.expected).slice(0, 128)}`);
+    }
 
-    super(message);
     this.generatedMessage = !options.message;
     this.name = 'AssertionError [ERR_ASSERTION]';
     this.code = 'ERR_ASSERTION';
@@ -63,15 +54,16 @@ class AssertionError extends Error {
 }
 
 function message(key, args) {
-  const assert = lazyAssert();
+  if (assert === null) assert = require('assert');
   assert.strictEqual(typeof key, 'string');
-  const util = lazyUtil();
   const msg = messages.get(key);
   assert(msg, `An invalid error message key was used: ${key}.`);
-  let fmt = util.format;
+  let fmt;
   if (typeof msg === 'function') {
     fmt = msg;
   } else {
+    if (util === null) util = require('util');
+    fmt = util.format;
     if (args === undefined || args.length === 0)
       return msg;
     args.unshift(msg);
@@ -240,7 +232,6 @@ E('ERR_VALID_PERFORMANCE_ENTRY_TYPE',
 // Add new errors from here...
 
 function invalidArgType(name, expected, actual) {
-  const assert = lazyAssert();
   assert(name, 'name is required');
   var msg = `The "${name}" argument must be ${oneOf(expected, 'type')}`;
   if (arguments.length >= 3) {

lib/internal/process.js

@@ -1,15 +1,7 @@
 'use strict';
 
 const util = require('util');
-
-var _lazyConstants = null;
-
-function lazyConstants() {
-  if (!_lazyConstants) {
-    _lazyConstants = process.binding('constants').os.signals;
-  }
-  return _lazyConstants;
-}
+const constants = process.binding('constants').os.signals;
 
 const assert = process.assert = function(x, msg) {
   if (!x) throw new Error(msg || 'assertion error');
@@ -177,8 +169,8 @@ function setupKillAndExit() {
       err = process._kill(pid, 0);
     } else {
       sig = sig || 'SIGTERM';
-      if (lazyConstants()[sig]) {
-        err = process._kill(pid, lazyConstants()[sig]);
+      if (constants[sig]) {
+        err = process._kill(pid, constants[sig]);
       } else {
         throw new Error(`Unknown signal: ${sig}`);
       }
@@ -198,7 +190,7 @@ function setupSignalHandlers() {
   const signalWraps = {};
 
   function isSignal(event) {
-    return typeof event === 'string' && lazyConstants()[event] !== undefined;
+    return typeof event === 'string' && constants[event] !== undefined;
   }
 
   // Detect presence of a listener for the special signal types
@@ -212,7 +204,7 @@ function setupSignalHandlers() {
 
       wrap.onsignal = function() { process.emit(type); };
 
-      const signum = lazyConstants()[type];
+      const signum = constants[type];
       const err = wrap.start(signum);
       if (err) {
         wrap.close();

lib/internal/process/stdio.js

@@ -1,14 +1,8 @@
 'use strict';
 
-exports.setup = setupStdio;
-
-var errors;
+const errors = require('internal/errors');
 
-function lazyErrors() {
-  if (!errors)
-    errors = require('internal/errors');
-  return errors;
-}
+exports.setup = setupStdio;
 
 function setupStdio() {
   var stdin;
@@ -20,8 +14,7 @@ function setupStdio() {
     stdout = createWritableStdioStream(1);
     stdout.destroySoon = stdout.destroy;
     stdout._destroy = function(er, cb) {
-      // avoid errors if we already emitted
-      const errors = lazyErrors();
+      // Avoid errors if we already emitted
       er = er || new errors.Error('ERR_STDOUT_CLOSE');
       cb(er);
     };
@@ -36,8 +29,7 @@ function setupStdio() {
     stderr = createWritableStdioStream(2);
     stderr.destroySoon = stderr.destroy;
     stderr._destroy = function(er, cb) {
-      // avoid errors if we already emitted
-      const errors = lazyErrors();
+      // Avoid errors if we already emitted
       er = er || new errors.Error('ERR_STDERR_CLOSE');
       cb(er);
     };
@@ -95,7 +87,6 @@ function setupStdio() {
 
       default:
         // Probably an error on in uv_guess_handle()
-        const errors = lazyErrors();
         throw new errors.Error('ERR_UNKNOWN_STDIN_TYPE');
     }
 
@@ -180,7 +171,6 @@ function createWritableStdioStream(fd) {
 
     default:
       // Probably an error on in uv_guess_handle()
-      const errors = lazyErrors();
       throw new errors.Error('ERR_UNKNOWN_STREAM_TYPE');
   }
 

lib/internal/process/warning.js

@@ -2,26 +2,16 @@
 
 const config = process.binding('config');
 const prefix = `(${process.release.name}:${process.pid}) `;
+const errors = require('internal/errors');
 
 exports.setup = setupProcessWarnings;
 
-var errors;
-var fs;
 var cachedFd;
 var acquiringFd = false;
 function nop() {}
 
-function lazyErrors() {
-  if (!errors)
-    errors = require('internal/errors');
-  return errors;
-}
-
-function lazyFs() {
-  if (!fs)
-    fs = require('fs');
-  return fs;
-}
+// Lazily loaded
+var fs = null;
 
 function writeOut(message) {
   if (console && typeof console.error === 'function')
@@ -31,7 +21,8 @@ function writeOut(message) {
 
 function onClose(fd) {
   return function() {
-    lazyFs().close(fd, nop);
+    if (fs === null) fs = require('fs');
+    fs.close(fd, nop);
   };
 }
 
@@ -53,14 +44,16 @@ function onAcquired(message) {
   return function(err, fd) {
     if (err)
       return writeOut(message);
-    lazyFs().appendFile(fd, `${message}\n`, nop);
+    if (fs === null) fs = require('fs');
+    fs.appendFile(fd, `${message}\n`, nop);
   };
 }
 
 function acquireFd(cb) {
   if (cachedFd === undefined && !acquiringFd) {
     acquiringFd = true;
-    lazyFs().open(config.warningFile, 'a', onOpen(cb));
+    if (fs === null) fs = require('fs');
+    fs.open(config.warningFile, 'a', onOpen(cb));
   } else if (cachedFd !== undefined && !acquiringFd) {
     cb(null, cachedFd);
   } else {
@@ -112,7 +105,6 @@ function setupProcessWarnings() {
   // process.emitWarning(str[, type[, code]][, ctor])
   // process.emitWarning(str[, options])
   process.emitWarning = function(warning, type, code, ctor, now) {
-    const errors = lazyErrors();
     var detail;
     if (type !== null && typeof type === 'object' && !Array.isArray(type)) {
       ctor = type.ctor;

lib/net.js

@@ -43,9 +43,11 @@ const async_id_symbol = process.binding('async_wrap').async_id_symbol;
 const { newUid, setInitTriggerId } = require('async_hooks');
 const nextTick = require('internal/process/next_tick').nextTick;
 const errors = require('internal/errors');
+const dns = require('dns');
 
-var cluster;
-var dns;
+// `cluster` is only used by `listenInCluster` so for startup performance
+// reasons it's lazy loaded.
+var cluster = null;
 
 const errnoException = util._errnoException;
 const exceptionWithHostPort = util._exceptionWithHostPort;
@@ -1023,7 +1025,6 @@ Socket.prototype.connect = function(...args) {
 
 
 function lookupAndConnect(self, options) {
-  const dns = lazyDns();
   var host = options.host || 'localhost';
   var port = options.port;
   var localAddress = options.localAddress;
@@ -1371,18 +1372,11 @@ function emitListeningNT(self) {
 }
 
 
-function lazyDns() {
-  if (dns === undefined)
-    dns = require('dns');
-  return dns;
-}
-
-
 function listenInCluster(server, address, port, addressType,
                          backlog, fd, exclusive) {
   exclusive = !!exclusive;
 
-  if (!cluster) cluster = require('cluster');
+  if (cluster === null) cluster = require('cluster');
 
   if (cluster.isMaster || exclusive) {
     // Will create a new handle
@@ -1491,7 +1485,6 @@ Server.prototype.listen = function(...args) {
 };
 
 function lookupAndListen(self, port, address, backlog, exclusive) {
-  const dns = lazyDns();
   dns.lookup(address, function doListen(err, ip, addressType) {
     if (err) {
       self.emit('error', err);

lib/readline.js

@@ -28,8 +28,9 @@
 'use strict';
 
 const { debug, inherits } = require('util');
-const Buffer = require('buffer').Buffer;
+const { Buffer } = require('buffer');
 const EventEmitter = require('events');
+const { StringDecoder } = require('string_decoder');
 const {
   CSI,
   emitKeys,
@@ -59,7 +60,6 @@ const ESCAPE_DECODER = Symbol('escape-decoder');
 // GNU readline library - keyseq-timeout is 500ms (default)
 const ESCAPE_CODE_TIMEOUT = 500;
 
-
 function createInterface(input, output, completer, terminal) {
   return new Interface(input, output, completer, terminal);
 }
@@ -177,7 +177,6 @@ function Interface(input, output, completer, terminal) {
       input.removeListener('data', ondata);
       input.removeListener('end', onend);
     });
-    var StringDecoder = require('string_decoder').StringDecoder; // lazy load
     this._decoder = new StringDecoder('utf8');
 
   } else {
@@ -979,7 +978,6 @@ Interface.prototype._ttyWrite = function(s, key) {
 
 function emitKeypressEvents(stream, iface) {
   if (stream[KEYPRESS_DECODER]) return;
-  var StringDecoder = require('string_decoder').StringDecoder; // lazy load
   stream[KEYPRESS_DECODER] = new StringDecoder('utf8');
 
   stream[ESCAPE_DECODER] = emitKeys(stream);