timers: run nextTicks after each immediate and timer

benchmark/timers/timers-timeout-nexttick.js

@@ -0,0 +1,36 @@
+'use strict';
+const common = require('../common.js');
+
+// The following benchmark measures setting up n * 1e6 timeouts,
+// as well as scheduling a next tick from each timeout. Those
+// then get executed on the next uv tick.
+
+const bench = common.createBenchmark(main, {
+  n: [5e4, 5e6],
+});
+
+function main({ n }) {
+  let count = 0;
+
+  // Function tracking on the hidden class in V8 can cause misleading
+  // results in this benchmark if only a single function is used —
+  // alternate between two functions for a fairer benchmark.
+
+  function cb() {
+    process.nextTick(counter);
+  }
+  function cb2() {
+    process.nextTick(counter);
+  }
+  function counter() {
+    count++;
+    if (count === n)
+      bench.end(n);
+  }
+
+  for (var i = 0; i < n; i++) {
+    setTimeout(i % 2 ? cb : cb2, 1);
+  }
+
+  bench.start();
+}

doc/api/process.md

@@ -1461,13 +1461,11 @@ changes:
 * `callback` {Function}
 * `...args` {any} Additional arguments to pass when invoking the `callback`
 
-The `process.nextTick()` method adds the `callback` to the "next tick queue".
-Once the current turn of the event loop turn runs to completion, all callbacks
-currently in the next tick queue will be called.
-
-This is *not* a simple alias to [`setTimeout(fn, 0)`][]. It is much more
-efficient. It runs before any additional I/O events (including
-timers) fire in subsequent ticks of the event loop.
+`process.nextTick()` adds `callback` to the "next tick queue". This queue is
+fully drained after the current operation on the JavaScript stack runs to
+completion and before the event loop is allowed to continue. As a result, it's
+possible to create an infinite loop if one were to recursively call
+`process.nextTick()`.
 
 ```js
 console.log('start');
@@ -1542,11 +1540,6 @@ function definitelyAsync(arg, cb) {
 }
 ```
 
-The next tick queue is completely drained on each pass of the event loop
-**before** additional I/O is processed. As a result, recursively setting
-`nextTick()` callbacks will block any I/O from happening, just like a
-`while(true);` loop.
-
 ## process.noDeprecation
 <!-- YAML
 added: v0.8.0
@@ -2162,7 +2155,6 @@ cases:
 [`require()`]: globals.html#globals_require
 [`require.main`]: modules.html#modules_accessing_the_main_module
 [`require.resolve()`]: modules.html#modules_require_resolve_request_options
-[`setTimeout(fn, 0)`]: timers.html#timers_settimeout_callback_delay_args
 [`v8.setFlagsFromString()`]: v8.html#v8_v8_setflagsfromstring_flags
 [Android building]: https://github.com/nodejs/node/blob/master/BUILDING.md#androidandroid-based-devices-eg-firefox-os
 [Child Process]: child_process.html

lib/internal/process/next_tick.js

@@ -26,7 +26,7 @@ function setupNextTick(_setupNextTick, _setupPromises) {
   const [
     tickInfo,
     runMicrotasks
-  ] = _setupNextTick(_tickCallback);
+  ] = _setupNextTick(internalTickCallback);
 
   // *Must* match Environment::TickInfo::Fields in src/env.h.
   const kHasScheduled = 0;
@@ -39,6 +39,15 @@ function setupNextTick(_setupNextTick, _setupPromises) {
   process._tickCallback = _tickCallback;
 
   function _tickCallback() {
+    if (tickInfo[kHasScheduled] === 0 && tickInfo[kHasPromiseRejections] === 0)
+      runMicrotasks();
+    if (tickInfo[kHasScheduled] === 0 && tickInfo[kHasPromiseRejections] === 0)
+      return;
+
+    internalTickCallback();
+  }
+
+  function internalTickCallback() {
     let tock;
     do {
       while (tock = queue.shift()) {

lib/timers.js

@@ -254,16 +254,17 @@ function processTimers(now) {
   debug('process timer lists %d', now);
   nextExpiry = Infinity;
 
-  let list, ran;
+  let list;
+  let ranAtLeastOneList = false;
   while (list = queue.peek()) {
     if (list.expiry > now) {
       nextExpiry = list.expiry;
       return refCount > 0 ? nextExpiry : -nextExpiry;
     }
-    if (ran)
+    if (ranAtLeastOneList)
       runNextTicks();
     else
-      ran = true;
+      ranAtLeastOneList = true;
     listOnTimeout(list, now);
   }
   return 0;
@@ -275,6 +276,7 @@ function listOnTimeout(list, now) {
   debug('timeout callback %d', msecs);
 
   var diff, timer;
+  let ranAtLeastOneTimer = false;
   while (timer = L.peek(list)) {
     diff = now - timer._idleStart;
 
@@ -288,6 +290,11 @@ function listOnTimeout(list, now) {
       return;
     }
 
+    if (ranAtLeastOneTimer)
+      runNextTicks();
+    else
+      ranAtLeastOneTimer = true;
+
     // The actual logic for when a timeout happens.
     L.remove(timer);
 
@@ -307,7 +314,33 @@ function listOnTimeout(list, now) {
 
     emitBefore(asyncId, timer[trigger_async_id_symbol]);
 
-    tryOnTimeout(timer);
+    let start;
+    if (timer._repeat)
+      start = getLibuvNow();
+
+    try {
+      const args = timer._timerArgs;
+      if (!args)
+        timer._onTimeout();
+      else
+        Reflect.apply(timer._onTimeout, timer, args);
+    } finally {
+      if (timer._repeat && timer._idleTimeout !== -1) {
+        timer._idleTimeout = timer._repeat;
+        if (start === undefined)
+          start = getLibuvNow();
+        insert(timer, timer[kRefed], start);
+      } else {
+        if (timer[kRefed])
+          refCount--;
+        timer[kRefed] = null;
+
+        if (destroyHooksExist() && !timer._destroyed) {
+          emitDestroy(timer[async_id_symbol]);
+          timer._destroyed = true;
+        }
+      }
+    }
 
     emitAfter(asyncId);
   }
@@ -327,30 +360,6 @@ function listOnTimeout(list, now) {
 }
 
 
-// An optimization so that the try/finally only de-optimizes (since at least v8
-// 4.7) what is in this smaller function.
-function tryOnTimeout(timer, start) {
-  if (start === undefined && timer._repeat)
-    start = getLibuvNow();
-  try {
-    ontimeout(timer);
-  } finally {
-    if (timer._repeat) {
-      rearm(timer, start);
-    } else {
-      if (timer[kRefed])
-        refCount--;
-      timer[kRefed] = null;
-
-      if (destroyHooksExist() && !timer._destroyed) {
-        emitDestroy(timer[async_id_symbol]);
-        timer._destroyed = true;
-      }
-    }
-  }
-}
-
-
 // Remove a timer. Cancels the timeout and resets the relevant timer properties.
 function unenroll(item) {
   // Fewer checks may be possible, but these cover everything.
@@ -456,26 +465,6 @@ setTimeout[internalUtil.promisify.custom] = function(after, value) {
 exports.setTimeout = setTimeout;
 
 
-function ontimeout(timer) {
-  const args = timer._timerArgs;
-  if (typeof timer._onTimeout !== 'function')
-    return Promise.resolve(timer._onTimeout, args[0]);
-  if (!args)
-    timer._onTimeout();
-  else
-    Reflect.apply(timer._onTimeout, timer, args);
-}
-
-function rearm(timer, start) {
-  // Do not re-arm unenroll'd or closed timers.
-  if (timer._idleTimeout === -1)
-    return;
-
-  timer._idleTimeout = timer._repeat;
-  insert(timer, timer[kRefed], start);
-}
-
-
 const clearTimeout = exports.clearTimeout = function clearTimeout(timer) {
   if (timer && timer._onTimeout) {
     timer._onTimeout = null;
@@ -601,75 +590,63 @@ function processImmediate() {
   const queue = outstandingQueue.head !== null ?
     outstandingQueue : immediateQueue;
   var immediate = queue.head;
-  const tail = queue.tail;
 
   // Clear the linked list early in case new `setImmediate()` calls occur while
   // immediate callbacks are executed
-  queue.head = queue.tail = null;
-
-  let count = 0;
-  let refCount = 0;
+  if (queue !== outstandingQueue) {
+    queue.head = queue.tail = null;
+    immediateInfo[kHasOutstanding] = 1;
+  }
 
+  let prevImmediate;
+  let ranAtLeastOneImmediate = false;
   while (immediate !== null) {
-    immediate._destroyed = true;
+    if (ranAtLeastOneImmediate)
+      runNextTicks();
+    else
+      ranAtLeastOneImmediate = true;
 
-    const asyncId = immediate[async_id_symbol];
-    emitBefore(asyncId, immediate[trigger_async_id_symbol]);
+    // It's possible for this current Immediate to be cleared while executing
+    // the next tick queue above, which means we need to use the previous
+    // Immediate's _idleNext which is guaranteed to not have been cleared.
+    if (immediate._destroyed) {
+      outstandingQueue.head = immediate = prevImmediate._idleNext;
+      continue;
+    }
 
-    count++;
+    immediate._destroyed = true;
+
+    immediateInfo[kCount]--;
     if (immediate[kRefed])
-      refCount++;
+      immediateInfo[kRefCount]--;
     immediate[kRefed] = null;
 
-    tryOnImmediate(immediate, tail, count, refCount);
+    prevImmediate = immediate;
 
-    emitAfter(asyncId);
+    const asyncId = immediate[async_id_symbol];
+    emitBefore(asyncId, immediate[trigger_async_id_symbol]);
 
-    immediate = immediate._idleNext;
-  }
+    try {
+      const argv = immediate._argv;
+      if (!argv)
+        immediate._onImmediate();
+      else
+        Reflect.apply(immediate._onImmediate, immediate, argv);
+    } finally {
+      immediate._onImmediate = null;
 
-  immediateInfo[kCount] -= count;
-  immediateInfo[kRefCount] -= refCount;
-  immediateInfo[kHasOutstanding] = 0;
-}
+      if (destroyHooksExist())
+        emitDestroy(asyncId);
 
-// An optimization so that the try/finally only de-optimizes (since at least v8
-// 4.7) what is in this smaller function.
-function tryOnImmediate(immediate, oldTail, count, refCount) {
-  var threw = true;
-  try {
-    // make the actual call outside the try/finally to allow it to be optimized
-    runCallback(immediate);
-    threw = false;
-  } finally {
-    immediate._onImmediate = null;
-
-    if (destroyHooksExist()) {
-      emitDestroy(immediate[async_id_symbol]);
+      outstandingQueue.head = immediate = immediate._idleNext;
     }
 
-    if (threw) {
-      immediateInfo[kCount] -= count;
-      immediateInfo[kRefCount] -= refCount;
-
-      if (immediate._idleNext !== null) {
-        // Handle any remaining Immediates after error handling has resolved,
-        // assuming we're still alive to do so.
-        outstandingQueue.head = immediate._idleNext;
-        outstandingQueue.tail = oldTail;
-        immediateInfo[kHasOutstanding] = 1;
-      }
-    }
+    emitAfter(asyncId);
   }
-}
 
-function runCallback(timer) {
-  const argv = timer._argv;
-  if (typeof timer._onImmediate !== 'function')
-    return Promise.resolve(timer._onImmediate, argv[0]);
-  if (!argv)
-    return timer._onImmediate();
-  Reflect.apply(timer._onImmediate, timer, argv);
+  if (queue === outstandingQueue)
+    outstandingQueue.head = null;
+  immediateInfo[kHasOutstanding] = 0;
 }
 
 

test/message/events_unhandled_error_nexttick.out

@@ -14,6 +14,7 @@ Error
     at bootstrapNodeJSCore (internal/bootstrap/node.js:*:*)
 Emitted 'error' event at:
     at process.nextTick (*events_unhandled_error_nexttick.js:*:*)
+    at internalTickCallback (internal/process/next_tick.js:*:*)
     at process._tickCallback (internal/process/next_tick.js:*:*)
     at Function.Module.runMain (internal/modules/cjs/loader.js:*:*)
     at startup (internal/bootstrap/node.js:*:*)

test/message/nexttick_throw.out

@@ -4,6 +4,7 @@
         ^
 ReferenceError: undefined_reference_error_maker is not defined
     at *test*message*nexttick_throw.js:*:*
+    at internalTickCallback (internal/process/next_tick.js:*:*)
     at process._tickCallback (internal/process/next_tick.js:*:*)
     at Function.Module.runMain (internal/modules/cjs/loader.js:*:*)
     at startup (internal/bootstrap/node.js:*:*)