Fix timers cancel in interval v4.x

lib/timers.js

@@ -272,14 +272,18 @@ exports.setInterval = function(callback, repeat) {
   return timer;
 
   function wrapper() {
+    // If _repeat was overriden we are effectively canceled. Bail.
+    if (typeof timer._repeat !== 'function')
+      return;
+
     timer._repeat();
 
-    // Timer might be closed - no point in restarting it
-    if (!timer._repeat)
+    // Do not re-arm unenroll'd or closed timers.
+    if (timer._idleTimeout === -1)
       return;
 
     // If timer is unref'd (or was - it's permanently removed from the list.)
-    if (this._handle) {
+    if (this._handle && timer instanceof Timeout) {
       this._handle.start(repeat, 0);
     } else {
       timer._idleTimeout = repeat;
@@ -309,9 +313,17 @@ const Timeout = function(after) {
 
 
 function unrefdHandle() {
-  this.owner._onTimeout();
-  if (!this.owner._repeat)
+  // Don't attempt to call the callback if it is not a function.
+  if (typeof this.owner._onTimeout === 'function') {
+    this.owner._onTimeout();
+  }
+
+  // Make sure we clean up if the callback is no longer a function
+  // even if the timer is an interval.
+  if (!this.owner._repeat
+      || typeof this.owner._onTimeout !== 'function') {
     this.owner.close();
+  }
 }
 
 
@@ -351,6 +363,7 @@ Timeout.prototype.ref = function() {
 Timeout.prototype.close = function() {
   this._onTimeout = null;
   if (this._handle) {
+    this._idleTimeout = -1;
     this._handle[kOnTimeout] = null;
     this._handle.close();
   } else {

test/parallel/test-timers-unenroll-unref-interval.js

@@ -0,0 +1,63 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const timers = require('timers');
+
+{
+  const interval = setInterval(common.mustCall(() => {
+    clearTimeout(interval);
+  }), 1).unref();
+}
+
+{
+  const interval = setInterval(common.mustCall(() => {
+    interval.close();
+  }), 1).unref();
+}
+
+{
+  const interval = setInterval(common.mustCall(() => {
+    timers.unenroll(interval);
+  }), 1).unref();
+}
+
+{
+  const interval = setInterval(common.mustCall(() => {
+    interval._idleTimeout = -1;
+  }), 1).unref();
+}
+
+{
+  const interval = setInterval(common.mustCall(() => {
+    interval._onTimeout = null;
+  }), 1).unref();
+}
+
+{
+  const interval = setInterval(common.mustCall(() => {
+    // This case is only necessary / valid prior to
+    // c8c2544cd9c339cdde881fc9a7f0851971b94d72
+    // which is not on the v4.x branch.
+    assert.strictEqual(typeof interval._repeat, 'function');
+
+    process.nextTick(common.mustCall(() => {
+      interval._repeat = null;
+    }));
+  }), 1).unref();
+}
+
+// Use timers' intrinsic behavior to keep this open
+// exactly long enough for the problem to manifest.
+//
+// See https://github.com/nodejs/node/issues/9561
+//
+// Since this is added after it will always fire later
+// than the previous timeouts, unrefed or not.
+//
+// Keep the event loop alive for one timeout and then
+// another. Any problems will occur when the second
+// should be called but before it is able to be.
+setTimeout(common.mustCall(() => {
+  setTimeout(common.mustCall(() => {}), 1);
+}), 1);