940217 - JavaScript Error: "A promise chain failed to handle a rejection.": [object StopIteration] from osfile_async_front.jsm

Status: RESOLVED FIXED

(Toolkit Graveyard :: OS.File, defect)

Description

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

Attachment: fix-promise-error

I get tons of these messages when I run tests:

TEST-INFO | chrome://mochitests/content/browser/browser/components/sessionstore/test/browser_636279.js | Console message: [JavaScript Error: "A promise chain failed to handle a rejection.

Date: Mon Nov 18 2013 20:06:40 GMT-0800 (PST)
Full Message: [object StopIteration]
Full Stack: JS frame :: resource://gre/modules/osfile/osfile_async_front.jsm :: withIterator :: line 1032
JS frame :: resource://gre/modules/Promise.jsm :: Handler.prototype.process :: line 767
JS frame :: resource://gre/modules/Promise.jsm :: this.PromiseWalker.walkerLoop :: line 531
native frame :: <unknown filename> :: <TOP_LEVEL> :: line 0"]


The problem is that DirectoryIterator is creating a rejected StopIteration promise that may never be used. This patch changes the code to create the promise more lazily. It seems to eliminate the errors.

Comment 1

[David Teller [:Yoric] - still alive but not very active]

Comment on attachment 8334356 [details] [diff] [review]
fix-promise-error

Review of attachment 8334356 [details] [diff] [review]:
-----------------------------------------------------------------

::: toolkit/components/osfile/modules/osfile_async_front.jsm
@@ +893,5 @@
> +  // Once close() is called, itmsg should reject with a
> +  // StopIteration. However, we don't want to create the promise until
> +  // it's needed because it might never be used. In that case, we
> +  // would get a warning on the console.
> +  get itmsg() {

It's a private field, so please prefix it with "_".

@@ +895,5 @@
> +  // it's needed because it might never be used. In that case, we
> +  // would get a warning on the console.
> +  get itmsg() {
> +    if (!this._itmsg)
> +      this._itmsg = Promise.reject(StopIteration);

Nit: braces.

@@ +896,5 @@
> +  // would get a warning on the console.
> +  get itmsg() {
> +    if (!this._itmsg)
> +      this._itmsg = Promise.reject(StopIteration);
> +    return this._itmsg;

So _itmsg should become something along the lines of __itmsg. Alternatively, make |get itmsg| a lazy getter that deletes/overwrites itself.

Comment 2

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

Attachment: fix-promise-error v2

Comment 3

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/68b341d7100d

Comment 4

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/68b341d7100d