timers: fix timeout when added in timer's callback

When a timer is added in another timer's callback, its underlying timer
handle will be started with a timeout that is actually incorrect.

The reason is that  the value that represents the current time is not
updated between the time the original callback is called and the time
the added timer is processed by timers.listOnTimeout. That leads the
logic in timers.listOnTimeout to do an incorrect computation that makes
the added timer fire with a timeout of scheduledTimeout +
timeSpentInCallback.

This change fixes that and make timers scheduled within other timers'
callbacks fire as expected.

Fixes nodejs#9333 and nodejs#15447.

lib/timers.js

@@ -83,10 +83,24 @@ function listOnTimeout() {
   debug('timeout callback ' + msecs);
 
   var now = Timer.now();
-  debug('now: ' + now);
+  // now's value has been updated, consider that it doesn't need to be updated
+  // unless a timer is added within the loop that processes the timers list
+  // below
+  list._addedTimer = false;
+  debug('now: %d', now);
 
   var first;
   while (first = L.peek(list)) {
+    // If the previous iteration caused a timer to be added,
+    // update the value of "now" so that timing computations are
+    // done correctly. See test/simple/test-timers-blocking-callback.js
+    // for more information.
+    if (list._addedTimer) {
+      now = Timer.now();
+      debug('now: %d', now);
+      list._addedTimer = false;
+    }
+
     var diff = now - first._monotonicStartTime;
     if (diff < msecs) {
       list.start(msecs - diff, 0);
@@ -182,6 +196,14 @@ exports.active = function(item) {
       item._monotonicStartTime = Timer.now();
       L.append(list, item);
     }
+
+    list = lists[msecs];
+    // Set _addedTimer so that listOnTimeout can refresh
+    // its current time value to avoid wrong timing computation
+    // in case timers callback block for a while.
+    // See test/simple/test-timers-blocking-callback.js for more
+    // details
+    list._addedTimer = true;
   }
 };
 

test/common.js

@@ -218,3 +218,11 @@ exports.hasMultiLocalhost = function hasMultiLocalhost() {
   t.close();
   return ret === 0;
 };
+
+exports.busyLoop = function busyLoop(time) {
+  var startTime = new Date().getTime();
+  var stopTime =  startTime + time;
+  while (new Date().getTime() < stopTime) {
+    ;
+  }
+};

test/simple/test-timers-blocking-callback.js

@@ -0,0 +1,99 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+/*
+ * This is a regression test for https://github.com/joyent/node/issues/15447
+ * and https://github.com/joyent/node/issues/9333.
+ *
+ * When a timer is added in another timer's callback, its underlying timer
+ * handle was started with a timeout that was actually incorrect.
+ *
+ * The reason was that the value that represents the current time was not
+ * updated between the time the original callback was called and the time
+ * the added timer was processed by timers.listOnTimeout. That lead the
+ * logic in timers.listOnTimeout to do an incorrect computation that made
+ * the added timer fire with a timeout of scheduledTimeout +
+ * timeSpentInCallback.
+ *
+ * This test makes sure that a timer added by another timer's callback
+ * fire with the expected timeout.
+ *
+ * It makes sure that it works when the timers list for a given timeout is
+ * empty (see testAddingTimerToEmptyTimersList) and when the timers list
+ * is not empty (see testAddingTimerToNonEmptyTimersList).
+ */
+
+var assert = require('assert');
+var common = require('../common');
+
+var TIMEOUT = 100;
+
+var nbBlockingCallbackCalls = 0;
+var latestDelay = 0;
+var timeCallbackScheduled = 0;
+
+function initTest() {
+  nbBlockingCallbackCalls = 0;
+  latestDelay = 0;
+  timeCallbackScheduled = 0;
+}
+
+function blockingCallback(callback) {
+  ++nbBlockingCallbackCalls;
+
+  if (nbBlockingCallbackCalls > 1) {
+    latestDelay = new Date().getTime() - timeCallbackScheduled;
+    // Even if timers can fire later than when they've been scheduled
+    // to fire, they should more than 50% later with a timeout of
+    // 100ms. Firing later than that would mean that we hit the regression
+    // highlighted in
+    // https://github.com/joyent/node/issues/15447 and
+    // https://github.com/joyent/node/issues/9333.
+    assert(latestDelay < TIMEOUT * 1.5);
+    if (callback)
+      return callback();
+  } else {
+    // block by busy-looping to trigger the issue
+    common.busyLoop(TIMEOUT);
+
+    timeCallbackScheduled = new Date().getTime();
+    setTimeout(blockingCallback, TIMEOUT);
+  }
+}
+
+function testAddingTimerToEmptyTimersList(callback) {
+  initTest();
+  // Call setTimeout just once to make sure the timers list is
+  // empty when blockingCallback is called.
+  setTimeout(blockingCallback.bind(global, callback), TIMEOUT);
+}
+
+function testAddingTimerToNonEmptyTimersList() {
+  initTest();
+  // Call setTimeout twice with the same timeout to make
+  // sure the timers list is not empty when blockingCallback is called.
+  setTimeout(blockingCallback, TIMEOUT);
+  setTimeout(blockingCallback, TIMEOUT);
+}
+
+// Run the test for the empty timers list case, and then for the non-empty
+// timers list one
+testAddingTimerToEmptyTimersList(testAddingTimerToNonEmptyTimersList);