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[camera] Run iOS methods on UI thread by default #4140

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merged 40 commits into from
Oct 20, 2021

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@renefloor renefloor commented Jul 7, 2021

In flutter/flutter#25959 we found that not everything in the iOS camera implementation should be run on the UI thread, as that blocks the app UI. The solution was to run everything on a different thread.

In flutter/flutter#52578 we found that we should not run everything on a different thread, because for example sending the result should be done on the UI thread.

In PR #4007 it is decided that things should run on UI thread by default and exceptions are made for heavy operations.

In flutter/flutter#25959 the author stated that "it's recommended that AVCaptureSession operations be called on a dedicated serial DispatchQueue". That means that initWithCameraName, start and stop need to be run on a different thread, but I'm not sure if these are the only ones blocking the UI.

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  • I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • I read the Tree Hygiene wiki page, which explains my responsibilities.
  • I read and followed the relevant style guides and ran the auto-formatter. (Note that unlike the flutter/flutter repo, the flutter/plugins repo does use dart format.)
  • I signed the CLA.
  • The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
  • I listed at least one issue that this PR fixes in the description above.
  • I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
  • I updated CHANGELOG.md to add a description of the change.
  • I updated/added relevant documentation (doc comments with ///).
  • I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
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renefloor and others added 2 commits July 14, 2021 09:17
@renefloor renefloor marked this pull request as ready for review July 14, 2021 07:58
packages/camera/camera/ios/Classes/CameraPlugin.m Outdated Show resolved Hide resolved
/**
Called when result is successful. Sends "successWithData" to the notification center.
*/
- (void)successWithData:(id)data {
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Shouldn't there be a thread assertion in this code?

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What do you mean with the thread assertion? That we verify that it is not the main thread?

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I don't remember what I meant by having that comment in this location unfortunately; maybe I was forgetting the flow and thinking this was after the bounce back to the main thread.

However, the more general questions is still valid: the goal of this PR is to ensure that methods are getting callbacks on the main thread, so why isn't there any code in the test that calls into the camera handler with a result object controlled by the test, and actually asserts that the callback was on the main thread? Like this: https://github.com/flutter/plugins/blob/master/packages/local_auth/example/ios/RunnerTests/FLTLocalAuthPluginTests.m#L62-L64

It is not clear to me what in this test would deterministically fail without the fix from this PR.

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@stuartmorgan I have now added ThreadSafeFlutterResultTests that test that the result is always called on the main thread. These tests in CameraMethodChannelTests just verify that ThreadSafeFlutterResult is used, not how that is working.

…ading

# Conflicts:
#	packages/camera/camera/CHANGELOG.md
#	packages/camera/camera/ios/Classes/CameraPlugin.m
#	packages/camera/camera/pubspec.yaml
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Looks good overall, mostly just nits around test fixtures.

@@ -23,6 +23,11 @@ - (void)setUp {
self.cameraPlugin = [[CameraPlugin alloc] initWithRegistry:nil messenger:self.mockMessenger];
}

- (void)tearDown {
self.mockMessenger = nil;
self.cameraPlugin = nil;
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I would actually much rather the ivars, the setup, and the teardown all be removed, and those two lines move into the test. Per the article I linked in a recent PR comment, stateless fixtures >> stateful fixtures, and in this case we're only saving two lines of boilerplate (assuming we eventually have more tests in this file; right now this is actually more code in order to theoretically reduce future duplication.)

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Done.


@interface CameraMethodChannelTests : XCTestCase
@property(readonly, nonatomic) CameraPlugin *camera;
@property(readonly, nonatomic) MockFLTThreadSafeFlutterResult *resultObject;
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Per the comment in the other file: please remove these and make them local to the test. (Having the object under test be part of the fixture state is always a major red flag to me unless there's a very compelling reason.)

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Done.

@end

@implementation CameraPreviewPauseTests

- (void)setUp {
_camera = [[FLTCam alloc] init];

_resultObject = [[MockFLTThreadSafeFlutterResult alloc] init];
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This should be local (and while you're here, you could move _camera into the tests. It's one line, and locality of setup of the object under test is absolutely worth one extra line of boilerplate.)

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Done.

* read the received result.
*/
@interface MockFLTThreadSafeFlutterResult : FLTThreadSafeFlutterResult
@property(readonly, nonatomic) XCTestExpectation *_Nonnull expectation;
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Can't this use the nonnull @property decoration?

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Yes this is possible, I used the Xcode "Fix" feature when the analyser warned me to specify a nonnull attribute and it added the _Nonnull declaration behind the pointer. It can be replaced with the nonnull attribute in the @property aswell (see update).

@@ -14,6 +15,7 @@
NS_DESIGNATED_INITIALIZER;
- (instancetype)init NS_UNAVAILABLE;

- (void)handleMethodCallAsync:(FlutterMethodCall *)call result:(FLTThreadSafeFlutterResult *)result;
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Needs a declaration comment.

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Done.

@@ -14,6 +15,7 @@
NS_DESIGNATED_INITIALIZER;
- (instancetype)init NS_UNAVAILABLE;

- (void)handleMethodCallAsync:(FlutterMethodCall *)call result:(FLTThreadSafeFlutterResult *)result;
- (void)orientationChanged:(NSNotification *)notification;
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Blank line between methods please.

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Done.

/**
* Gets the original FlutterResult object wrapped by this FLTThreadSafeFlutterResult instance.
*/
@property(readonly, nonatomic) FlutterResult _Nonnull flutterResult;
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nonnull

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Done.

@property(readonly, nonatomic) XCTestExpectation *_Nonnull expectation;
@property(nonatomic, nullable) id receivedResult;

- (instancetype _Nonnull)initWithExpectation:(XCTestExpectation *_Nonnull)expectation;
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These should be nonnull as well.

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Done.

* Initializes with a FlutterResult object.
* @param result The FlutterResult object that the result will be given to.
*/
- (nonnull id)initWithResult:(nonnull FlutterResult)result;
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instancetype

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Fixed.

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@stuartmorgan I resolved all nits, would appreciate it if you could have another look.


@interface CameraMethodChannelTests : XCTestCase
@property(readonly, nonatomic) CameraPlugin *camera;
@property(readonly, nonatomic) MockFLTThreadSafeFlutterResult *resultObject;
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Done.

@@ -23,6 +23,11 @@ - (void)setUp {
self.cameraPlugin = [[CameraPlugin alloc] initWithRegistry:nil messenger:self.mockMessenger];
}

- (void)tearDown {
self.mockMessenger = nil;
self.cameraPlugin = nil;
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Done.

@end

@implementation CameraPreviewPauseTests

- (void)setUp {
_camera = [[FLTCam alloc] init];

_resultObject = [[MockFLTThreadSafeFlutterResult alloc] init];
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Done.

* read the received result.
*/
@interface MockFLTThreadSafeFlutterResult : FLTThreadSafeFlutterResult
@property(readonly, nonatomic) XCTestExpectation *_Nonnull expectation;
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Yes this is possible, I used the Xcode "Fix" feature when the analyser warned me to specify a nonnull attribute and it added the _Nonnull declaration behind the pointer. It can be replaced with the nonnull attribute in the @property aswell (see update).

* Called when result is successful.
*
* Fulfills the expectation.
*/
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Removed.

@@ -14,6 +15,7 @@
NS_DESIGNATED_INITIALIZER;
- (instancetype)init NS_UNAVAILABLE;

- (void)handleMethodCallAsync:(FlutterMethodCall *)call result:(FLTThreadSafeFlutterResult *)result;
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Done.

@@ -14,6 +15,7 @@
NS_DESIGNATED_INITIALIZER;
- (instancetype)init NS_UNAVAILABLE;

- (void)handleMethodCallAsync:(FlutterMethodCall *)call result:(FLTThreadSafeFlutterResult *)result;
- (void)orientationChanged:(NSNotification *)notification;
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Done.

/**
* Gets the original FlutterResult object wrapped by this FLTThreadSafeFlutterResult instance.
*/
@property(readonly, nonatomic) FlutterResult _Nonnull flutterResult;
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Done.

* Initializes with a FlutterResult object.
* @param result The FlutterResult object that the result will be given to.
*/
- (nonnull id)initWithResult:(nonnull FlutterResult)result;
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Fixed.

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LGTM with some last nits. Thanks for getting this over the line!

XCTAssertNil(result);
[resultExpectation fulfill];
}];
[self waitForExpectationsWithTimeout:2.0 handler:nil];
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Don't you still need this (and an expectation passed to the MockFLTThreadSafeFlutterResult initialization) so that the assertions are guaranteed to run after the result callback?

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I don't think so, the [CameraPlugin pausePreviewWithResult:] method that is tested has a very simple (synchronised) implementation and will not run its logic on a different queue (dispatching on different queue is done by the [CameraPlugin handleMethodCall] method).

Also the result object that is passed in is a simple mock implementation of the FLTThreadSafeFlutterResult class which simply echo's the value that is received by calling the [MockFLTThreadSafeFlutterResult sendSuccessWithData:] method through the MockFLTThreadSafeFlutterResult.receivedResult property.

So as far as I understand everything will run synchronously after each other.

XCTAssertNil(result);
[resultExpectation fulfill];
}];
[self waitForExpectationsWithTimeout:2.0 handler:nil];
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Same.

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See explanation above.

* The expectation is fullfilled when a result is called allowing tests to await the result in an
* asynchronous manner.
*/
- (instancetype _Nonnull)initWithExpectation:(nonnull XCTestExpectation *)expectation;
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nonnull instancetype

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Fixed.

/// Exposes the [CameraPlugin handleMethodCallAsync:result:] method for unit testing.
///
/// This method should always be dispatched on a background queue to prevent deadlocks.

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Remove the blank line here please.

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Done.

- (instancetype)init NS_UNAVAILABLE;

/// Exposes the [CameraPlugin handleMethodCallAsync:result:] method for unit testing.
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The comments on these methods should be normal declaration comments explaining what the method actually does. The "exposed for unit testing" part belongs as a comment on the category itself (where it already is, correctly).

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Improved the documentation as suggested.

@mvanbeusekom mvanbeusekom added the waiting for tree to go green (Use "autosubmit") This PR is approved and tested, but waiting for the tree to be green to land. label Oct 18, 2021
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Changes LGTM (this didn't need another review round)

@fluttergithubbot fluttergithubbot merged commit b8aea6d into flutter:master Oct 20, 2021
engine-flutter-autoroll added a commit to engine-flutter-autoroll/flutter that referenced this pull request Oct 20, 2021
NickalasB added a commit to NickalasB/plugins that referenced this pull request Oct 21, 2021
* master:
  [webview] Fix typos in the README (flutter#4249)
  [google_sign_in] add serverAuthCode to GoogleSignInAccount (flutter#4180)
  [ci] Update macOS Cirrus image to Xcode 13 (flutter#4429)
  [shared_preferences] Switch to new analysis options (flutter#4384)
  [flutter_plugin_android_lifecycle] remove placeholder dart file (flutter#4413)
  [camera] Run iOS methods on UI thread by default (flutter#4140)
  [ci] Always run all `format` steps (flutter#4427)
  [flutter_plugin_tools] Fix license-check on Windows (flutter#4425)
  [google_maps_flutter] Clean Java test, consolidate Marker example. (flutter#4400)
  [image_picker][android] suppress unchecked warning (flutter#4408)
  [ci] Replace Firebase Test Lab deprecated Pixel 4 device with Pixel 5 (flutter#4436)
  [image_picker_for_web] Added support for maxWidth, maxHeight and imageQuality  (flutter#4389)
  Bump compileSdkVersion to 31 (flutter#4432)
  [camera] Update [CameraOrientationTests testOrientationNotifications] unit test to work on Xcode 13 (flutter#4426)
  Update integration_test README  (flutter#3824)
  [webview_flutter] Adjust test URLs again (flutter#4407)
  [google_sign_in] Add serverAuthCode attribute to google_sign_in_platform_interface user data (flutter#4179)
  [camera] Add filter for unsupported cameras on Android (flutter#4418)
NickalasB added a commit to NickalasB/plugins that referenced this pull request Oct 21, 2021
* master:
  [webview] Fix typos in the README (flutter#4249)
  [google_sign_in] add serverAuthCode to GoogleSignInAccount (flutter#4180)
  [ci] Update macOS Cirrus image to Xcode 13 (flutter#4429)
  [shared_preferences] Switch to new analysis options (flutter#4384)
  [flutter_plugin_android_lifecycle] remove placeholder dart file (flutter#4413)
  [camera] Run iOS methods on UI thread by default (flutter#4140)
  [ci] Always run all `format` steps (flutter#4427)
  [flutter_plugin_tools] Fix license-check on Windows (flutter#4425)
  [google_maps_flutter] Clean Java test, consolidate Marker example. (flutter#4400)
  [image_picker][android] suppress unchecked warning (flutter#4408)
  [ci] Replace Firebase Test Lab deprecated Pixel 4 device with Pixel 5 (flutter#4436)
  [image_picker_for_web] Added support for maxWidth, maxHeight and imageQuality  (flutter#4389)
  Bump compileSdkVersion to 31 (flutter#4432)
  [camera] Update [CameraOrientationTests testOrientationNotifications] unit test to work on Xcode 13 (flutter#4426)
  Update integration_test README  (flutter#3824)
  [webview_flutter] Adjust test URLs again (flutter#4407)
  [google_sign_in] Add serverAuthCode attribute to google_sign_in_platform_interface user data (flutter#4179)
  [camera] Add filter for unsupported cameras on Android (flutter#4418)

# Conflicts:
#	packages/webview_flutter/webview_flutter/CHANGELOG.md
#	packages/webview_flutter/webview_flutter/pubspec.yaml
yasargil added a commit to yasargil/plugins that referenced this pull request Oct 25, 2021
* master: (364 commits)
  Use OpenJDK 11 in CI jobs  (flutter#4419)
  [google_sign_in] remove the commented out code in tests (flutter#4442)
  [webview] Fix typos in the README (flutter#4249)
  [google_sign_in] add serverAuthCode to GoogleSignInAccount (flutter#4180)
  [ci] Update macOS Cirrus image to Xcode 13 (flutter#4429)
  [shared_preferences] Switch to new analysis options (flutter#4384)
  [flutter_plugin_android_lifecycle] remove placeholder dart file (flutter#4413)
  [camera] Run iOS methods on UI thread by default (flutter#4140)
  [ci] Always run all `format` steps (flutter#4427)
  [flutter_plugin_tools] Fix license-check on Windows (flutter#4425)
  [google_maps_flutter] Clean Java test, consolidate Marker example. (flutter#4400)
  [image_picker][android] suppress unchecked warning (flutter#4408)
  [ci] Replace Firebase Test Lab deprecated Pixel 4 device with Pixel 5 (flutter#4436)
  [image_picker_for_web] Added support for maxWidth, maxHeight and imageQuality  (flutter#4389)
  Bump compileSdkVersion to 31 (flutter#4432)
  [camera] Update [CameraOrientationTests testOrientationNotifications] unit test to work on Xcode 13 (flutter#4426)
  Update integration_test README  (flutter#3824)
  [webview_flutter] Adjust test URLs again (flutter#4407)
  [google_sign_in] Add serverAuthCode attribute to google_sign_in_platform_interface user data (flutter#4179)
  [camera] Add filter for unsupported cameras on Android (flutter#4418)
  ...

# Conflicts:
#	packages/google_maps_flutter/google_maps_flutter/android/src/main/java/io/flutter/plugins/googlemaps/GoogleMapController.java
hofmannfelix pushed a commit to hofmannfelix/plugins that referenced this pull request Oct 30, 2021
…ideo_src_on_same_controller

* commit '76e84c0679dbab7bfaaaa553b17bb0dbdb9a3c33': (537 commits)
  [video_player] Initialize player when size and duration become available (flutter#4438)
  [webview_flutter] Implement zoom enabled for ios and android (flutter#4417)
  Partial revert of "upgraded usage of BinaryMessenger (flutter#4451)" (flutter#4453)
  Implement Android WebView api with pigeon (Java portion) (flutter#4441)
  [in_app_purchase] Update to the latest pkg:json_serializable (flutter#4434)
  Implement Android WebView api with pigeon (Dart portion)  (flutter#4435)
  upgraded usage of BinaryMessenger (flutter#4451)
  [flutter_plugin_tools] Fix pubspec-check on Windows (flutter#4428)
  Use OpenJDK 11 in CI jobs  (flutter#4419)
  [google_sign_in] remove the commented out code in tests (flutter#4442)
  [webview] Fix typos in the README (flutter#4249)
  [google_sign_in] add serverAuthCode to GoogleSignInAccount (flutter#4180)
  [ci] Update macOS Cirrus image to Xcode 13 (flutter#4429)
  [shared_preferences] Switch to new analysis options (flutter#4384)
  [flutter_plugin_android_lifecycle] remove placeholder dart file (flutter#4413)
  [camera] Run iOS methods on UI thread by default (flutter#4140)
  [ci] Always run all `format` steps (flutter#4427)
  [flutter_plugin_tools] Fix license-check on Windows (flutter#4425)
  [google_maps_flutter] Clean Java test, consolidate Marker example. (flutter#4400)
  [image_picker][android] suppress unchecked warning (flutter#4408)
  ...

# Conflicts:
#	packages/video_player/video_player/pubspec.yaml
#	packages/video_player/video_player_web/lib/video_player_web.dart
#	packages/video_player/video_player_web/pubspec.yaml
amantoux pushed a commit to amantoux/plugins that referenced this pull request Dec 11, 2021
KyleFin pushed a commit to KyleFin/plugins that referenced this pull request Dec 21, 2021
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