Make StreamIterator not delay pausing between requests.

Make StreamIterator not delay pausing between requests.

The current implementation of StreamIterator has a one-element buffer which
allows it listen for the next even eagerly, and only pause if consumption
doesn't keep up with production.
However, StreamIterator is also used by both VM and dart2js implementations
of "await for", and according to the specification, the iterated stream
must be paused between loop iterations.

The CL removes the one-element buffer and forces a pause after each event.

R=floitsch@google.com

Committed: https://github.com/dart-lang/sdk/commit/caf208a54381ddaafb00d4f8b2910f7583e5faca

[Lasse Reichstein Nielsen, 2016-07-14 07:09:32]

lrn@google.com changed reviewers:
+ floitsch@google.com

[floitsch, 2016-07-14 13:29:25]

LGTM.

https://codereview.chromium.org/2149893002/diff/1/sdk/lib/async/stream_impl.dart
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/2149893002/diff/1/sdk/lib/async/stream_impl.d...
sdk/lib/async/stream_impl.dart:957: return _stateData;
Please make sure that this is still strong-mode clean.

[floitsch, 2016-07-14 13:32:01]

On 2016/07/14 13:29:25, floitsch wrote:
> LGTM.
> 
>
https://codereview.chromium.org/2149893002/diff/1/sdk/lib/async/stream_impl.dart
> File sdk/lib/async/stream_impl.dart (right):
> 
>
https://codereview.chromium.org/2149893002/diff/1/sdk/lib/async/stream_impl.d...
> sdk/lib/async/stream_impl.dart:957: return _stateData;
> Please make sure that this is still strong-mode clean.

Add tests, that `await for` now actually behaves like a synchronous loop.

[Lasse Reichstein Nielsen, 2016-07-14 13:49:58]

On 2016/07/14 13:32:01, floitsch wrote:
> > Please make sure that this is still strong-mode clean.

I hope the analyzer can answer that for core libraries too.

> Add tests, that `await for` now actually behaves like a synchronous loop.

Good idea.

I also have an idea to avoid some pauses without changing behavior (if
`moveNext` is called immediately in the future listener, there is no need to
pause), but I'll try that in a follow-up CL, and then it will be good to have
the test.

[Lasse Reichstein Nielsen, 2016-07-14 14:31:22]

Interestingly this only fixes the yield-problem for dart2js, the VM is
unaffected.
I'll dig deeper.

[Lasse Reichstein Nielsen, 2016-09-23 10:53:39]

PTAL

[floitsch, 2016-09-23 14:10:09]

LGTM.

https://codereview.chromium.org/2149893002/diff/60001/sdk/lib/async/stream_im...
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/2149893002/diff/60001/sdk/lib/async/stream_im...
sdk/lib/async/stream_impl.dart:916: * Pauses the stream between calles to
[moveNext].
calls

[Lasse Reichstein Nielsen, 2016-09-26 07:25:24]

https://codereview.chromium.org/2149893002/diff/60001/sdk/lib/async/stream_im...
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/2149893002/diff/60001/sdk/lib/async/stream_im...
sdk/lib/async/stream_impl.dart:916: * Pauses the stream between calles to
[moveNext].
On 2016/09/23 14:10:09, floitsch wrote:
> calls

Done.

[Lasse Reichstein Nielsen, 2016-09-26 07:35:53]

Description was changed from

==========
Make StreamIterator not delay pausing between requests.

The current implementation of StreamIterator has a one-element buffer which
allows it listen for the next even eagerly, and only pause if consumption
doesn't keep up with production.
However, StreamIterator is also used by both VM and dart2js implementations
of "await for", and according to the specification, the iterated stream
must be paused between loop iterations.

The CL removes the one-element buffer and forces a pause after each event.
==========

to

==========
Make StreamIterator not delay pausing between requests.

The current implementation of StreamIterator has a one-element buffer which
allows it listen for the next even eagerly, and only pause if consumption
doesn't keep up with production.
However, StreamIterator is also used by both VM and dart2js implementations
of "await for", and according to the specification, the iterated stream
must be paused between loop iterations.

The CL removes the one-element buffer and forces a pause after each event.

R=floitsch@google.com

Committed:
https://github.com/dart-lang/sdk/commit/caf208a54381ddaafb00d4f8b2910f7583e5faca
==========

[Lasse Reichstein Nielsen, 2016-09-26 07:35:55]

Committed patchset #5 (id:80001) manually as
caf208a54381ddaafb00d4f8b2910f7583e5faca (presubmit successful).