lib: fix guard expression in timer.unref()

Fixes the following assertion on slow systems, like our ARM buildbot:

    $ out/Debug/node test/simple/test-timers-unref.js
    node: ../src/async-wrap-inl.h:101: v8::Handle<v8::Value>
    node::AsyncWrap::MakeCallback(uint32_t, int,
    v8::Handle<v8::Value>*): Assertion `cb_v->IsFunction()' failed.
    Aborted

The reason it only manifests on slow systems is that the test starts
a 1 ms interval timer, then defers timer.unref.bind({}) to the next
tick.  On fast systems, the test completes in under a millisecond,
before the callback is called.

This commit makes timer.unref() check that the receiver actually has
a timeout callback property.

Fixes nodejs#13.

PR-URL: nodejs/node#165
Reviewed-By: Rod Vagg <rod@vagg.org>

lib/timers.js

@@ -287,7 +287,9 @@ var Timeout = function(after) {
 };
 
 Timeout.prototype.unref = function() {
-  if (!this._handle) {
+  if (this._handle) {
+    this._handle.unref();
+  } else if (typeof(this._onTimeout) === 'function') {
     var now = Timer.now();
     if (!this._idleStart) this._idleStart = now;
     var delay = this._idleStart + this._idleTimeout - now;
@@ -298,8 +300,6 @@ Timeout.prototype.unref = function() {
     this._handle.start(delay, 0);
     this._handle.domain = this.domain;
     this._handle.unref();
-  } else {
-    this._handle.unref();
   }
 };
 

test/parallel/test-timers-unref-call.js

@@ -0,0 +1,25 @@
+// Copyright (c) 2014, StrongLoop Inc.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+var common = require('../common');
+
+var Timer = process.binding('timer_wrap').Timer;
+Timer.now = function() { return ++Timer.now.ticks; };
+Timer.now.ticks = 0;
+
+var t = setInterval(function() {}, 1);
+var o = { _idleStart: 0, _idleTimeout: 1 };
+t.unref.call(o);
+
+setTimeout(clearInterval.bind(null, t), 2);