timers: fix eventloop block

When there are at least 2 timers set by setInterval whose callback
execution are longer than interval, the eventloop will be blocked.

This commit fix the above bug.

PR-URL: nodejs/node#15072
Fixes: nodejs/node#15068
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/timers.js

@@ -233,7 +233,7 @@ function listOnTimeout() {
     if (diff < msecs) {
       var timeRemaining = msecs - (TimerWrap.now() - timer._idleStart);
       if (timeRemaining < 0) {
-        timeRemaining = 0;
+        timeRemaining = 1;
       }
       this.start(timeRemaining);
       debug('%d list wait because diff is %d', msecs, diff);

test/sequential/test-timers-block-eventloop.js

@@ -0,0 +1,22 @@
+'use strict';
+
+const common = require('../common');
+const fs = require('fs');
+
+const t1 = setInterval(() => {
+  common.busyLoop(12);
+}, 10);
+
+const t2 = setInterval(() => {
+  common.busyLoop(15);
+}, 10);
+
+const t3 = setTimeout(common.mustNotCall('eventloop blocked!'), 100);
+
+setTimeout(function() {
+  fs.stat('./nonexistent.txt', (err, stats) => {
+    clearInterval(t1);
+    clearInterval(t2);
+    clearTimeout(t3);
+  });
+}, 50);