Fixed a crash in Objective-C clients when data channel becomes closed.

Fixed a crash in Objective-C clients when data channel becomes closed.

Objective-C applications using the data channel could crash when the following conditions were met:
 - The application creates a data channel and sets a data channel delegate
 - The delegate is deallocated but the application never clears it
When this happens, the dealloc method in RTCDataChannel would reset the delegate to nil. The setDelegate: method immediately returns if the new delegate value is the same as the old one. Since the old one is a weak reference, it becomes nil, and the DataChannelDelegateAdapter is not unsubscribed from the native channel before it gets deleted.

The fix removes the two optimizations, and instead subscribes the adapter to the native data channel at creation time - and unsubscribes it at dealloc time. This makes it very easy to reason about the lifetime of the subscription. Removing the optimization should have little effect on performance, as applications typically set the delegate when the channel is created.

BUG=

Committed: https://crrev.com/630d9ba364db875ee5a4b78a6e7f1fbaa0719b10
Cr-Commit-Position: refs/heads/master@{#12649}

[skvlad, 2016-05-06 20:55:08]

skvlad@webrtc.org changed reviewers:
+ haysc@webrtc.org, tkchin@webrtc.org

[tkchin_webrtc, 2016-05-06 21:13:28]

On 2016/05/06 20:55:09, skvlad wrote:

good work

lgtm

[skvlad, 2016-05-06 22:10:18]

The CQ bit was checked by skvlad@webrtc.org

[commit-bot: I haz the power, 2016-05-06 22:10:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1957523006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1957523006/1

[commit-bot: I haz the power, 2016-05-06 23:10:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-05-06 23:10:59]

Description was changed from

==========
Fixed a crash in Objective-C clients when data channel becomes closed.

Objective-C applications using the data channel could crash when the following
conditions were met:
 - The application creates a data channel and sets a data channel delegate
 - The delegate is deallocated but the application never clears it
When this happens, the dealloc method in RTCDataChannel would reset the delegate
to nil. The setDelegate: method immediately returns if the new delegate value is
the same as the old one. Since the old one is a weak reference, it becomes nil,
and the DataChannelDelegateAdapter is not unsubscribed from the native channel
before it gets deleted.

The fix removes the two optimizations, and instead subscribes the adapter to the
native data channel at creation time - and unsubscribes it at dealloc time. This
makes it very easy to reason about the lifetime of the subscription. Removing
the optimization should have little effect on performance, as applications
typically set the delegate when the channel is created.

BUG=
==========

to

==========
Fixed a crash in Objective-C clients when data channel becomes closed.

Objective-C applications using the data channel could crash when the following
conditions were met:
 - The application creates a data channel and sets a data channel delegate
 - The delegate is deallocated but the application never clears it
When this happens, the dealloc method in RTCDataChannel would reset the delegate
to nil. The setDelegate: method immediately returns if the new delegate value is
the same as the old one. Since the old one is a weak reference, it becomes nil,
and the DataChannelDelegateAdapter is not unsubscribed from the native channel
before it gets deleted.

The fix removes the two optimizations, and instead subscribes the adapter to the
native data channel at creation time - and unsubscribes it at dealloc time. This
makes it very easy to reason about the lifetime of the subscription. Removing
the optimization should have little effect on performance, as applications
typically set the delegate when the channel is created.

BUG=

Committed: https://crrev.com/630d9ba364db875ee5a4b78a6e7f1fbaa0719b10
Cr-Commit-Position: refs/heads/master@{#12649}
==========

[commit-bot: I haz the power, 2016-05-06 23:11:00]

Patchset 1 (id:??) landed as
https://crrev.com/630d9ba364db875ee5a4b78a6e7f1fbaa0719b10
Cr-Commit-Position: refs/heads/master@{#12649}