Make asBroadcastStream take two callbacks.

Make asBroadcastStream take two callbacks.

These callbacks will be called when the broadcast stream no longer
has any listeners, or when it gets a listener after having none.

The callback is provided with a StreamSubscription-like object where
it can pause/resume/cancel the underlying subscription on the original
stream.

BUG=http://dartbug.com/11289
R=floitsch@google.com

Committed: https://code.google.com/p/dart/source/detail?r=24776

[floitsch, 2013-06-20 14:28:30]

LGTM.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dart
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:737: _zone.executeCallback(() {
I'm not sure if these should be run in the zone: they are synchronous calls
(like the cancel handler).
If we think they should be, then it would need to be:
executePeriodicCallback
(the zone doesn't expect a callback)

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:745: _zone.executeCallback(() {
ditto.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:781: * that it is invalidated, so a user can't
hand on to it and change the
Description seems to be wrong. Pause and resume keep _stream non-null.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:805: if (_stream == null) return;
throw.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:806: _stream._pauseSubscription(resumeSignal);
This is a little bit strange: we allow a resume-signal, but we don't allow to
invoke 'resume' by ourselves?
For consistency I would say: no resumeSignal either.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:810: if (_stream == null) return;
ditto (throw).

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:815: if (_stream == null) return;
ditto.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:822: if (_stream == null) return false;
ditto.

[Lasse Reichstein Nielsen, 2013-06-21 09:49:11]

PTAL

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dart
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:737: _zone.executeCallback(() {
Zone has been removed from the callback.
Uses current zone's handleUncaughtError for errors.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:745: _zone.executeCallback(() {
On 2013/06/20 14:28:30, floitsch wrote:
> ditto.

Done.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:781: * that it is invalidated, so a user can't
hand on to it and change the
ACK, changed that but forgot the doc.
It stays valid. At some point the underlying subscription is canceled, and then
calling its pause/resume/cancel won't do anything, but that's all.

I've removed the "setting _stream to null" hackery since it won't do any good
anyway.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:805: if (_stream == null) return;
actually, I removed the line, and just call through in all cases.
The underlying subscription will ignore the calls when it is canceled anyway.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:806: _stream._pauseSubscription(resumeSignal);
We do allow calling resume.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:810: if (_stream == null) return;
Ditto, removed.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:815: if (_stream == null) return;
removed.

https://codereview.chromium.org/17490002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:822: if (_stream == null) return false;
Removed.

[Lasse Reichstein Nielsen, 2013-07-04 13:02:15]

Committed patchset #3 manually as r24776 (presubmit successful).