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This CL factors out the remaining responsibilities of TabModel and removes it. It introduces a functional change in how sessions are saved when scenes background. For the purposes of this code, "saving sessions" involves both updating the session store and writing out snapshots of the active web states. TabModels -- which were per-browser objects -- listed for the UIApplication lifecycle notifications to determine when to save sessions. This means that when the application backgrounds, all of the connected scenes save the sessions for the active webstates in their browsers. It also means that sessions are *not* saved when individual scenes background. (This is not the only trigger for saving sessions in Chrome, just the one determined by app/scene lifecycles). This CL changes this backgrounding logic, moving it to a scene state agent. This agent observes the scene state transitions, and now it saves sessions per-scene, whenever that scene backgrounds. The other responsibility of TabModel was to close all of the web states in a web state list when the owning Browser is shut down. This CL moves that responsibility to BrowserViewWrangler, which is the current owner of Browser lifecycles. Potentially it could be migrated to the BrowserImpl class in the future for even better encapsulation. Because there are some circumstances where the app may shut down without being backgrounded (if it is force-quit in the app switcher when no other apps are present, for example), this CL adds a check to the shutdown code in SceneController that asks the scene to save the session if needed. (Sessions are marked as needing saving if the scene has foregrounded since the previous save). Bug: 1045575, 1115611, 1110966, 783777 Change-Id: Ic70f4d1b839ab95757196a805ccac21c36b7dc83 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3063619 Commit-Queue: Mark Cogan <marq@chromium.org> Reviewed-by: Rohit Rao <rohitrao@chromium.org> Reviewed-by: Mohammad Refaat <mrefaat@chromium.org> Cr-Commit-Position: refs/heads/master@{#908028}
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| Original file line number | Diff line number | Diff line change |
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| ## Session saving and restoration. | ||
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| A *Session* is the data Chrome saves to an iOS device's storage that preserves | ||
| the state of open tabs in a given Browser. On a device that only supports a | ||
| single Chrome window, there will be one saved session for the regular tabs, | ||
| and one saved session for the Incognito tabs. On devices that support multiple | ||
| windows, there will be one or two (two if there are Incognito tabs) saved | ||
| sessions for each window. | ||
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| Sessions are the mechanism by which a user's open tabs are restored when they | ||
| laucnh Chrome. Given that iOS can terminate Chrome in the background at any | ||
| time -- and can disconnect individual scenes when there are multiple windows -- | ||
| it's critical that sessions are saved and restored in a way that is quick and | ||
| lossless for the user. | ||
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| (Don't confuse this Chrome-specific sense of *session* with the UIKit concept | ||
| of a *scene session*, implemented in the `UISceneSession` class. While both are | ||
| concerned with persisting application state data, they are not interchangeable, | ||
| and Chrome's sessions are not implemented using UISceneSessions for storage.) | ||
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| ### Session saving | ||
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| The design intent is that sessions are saved before Chrome enters a state where | ||
| it might be suddenly terminated. | ||
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| Saving a session is done by means of the `SessionRestorationBrowserAgent` for | ||
| the browser being saved, using the `SaveSession()` method. Calling this saves | ||
| the session for the browser the agent is attached to. | ||
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| <!-- Add details on how sessions are saved; this depends on if the iOS15 APIs | ||
| for saving WKWebView interactionState are being used or not. Also describe | ||
| how per-window session saving is done. --> | ||
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| `SaveSession()` is called in the following circumstances: | ||
| 1. Whenever a sene moves to the background, `SaveSession()` is called on its | ||
| browsers. | ||
| 2. When the UI for a scene is destroyed (when the scene's `SceneController` is | ||
| shutting down), `SaveSession()` is called if it hasn't been called aready. | ||
| 3. When a tab is inserted, removed, activated, replaced, re-ordered, or | ||
| completes a navigation, `SaveSession()` on the Browser that owns its | ||
| WebStateList. | ||
| 4. When a prerendered tab is loaded, replacing an existing webState, | ||
| `SaveSession()` on the browser whose WebStateList contains the new tab. | ||
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| Case (1) is handled by `SessionSavingSceneAgent`, which watches for scene state | ||
| changes and tracks if the current scene has been foregrounded since the last | ||
| time it was saved. Such scenes are marked as needing to have their sessions | ||
| saved the next time they background. | ||
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| Case (2) is handled by `SceneController` itself when it shuts down; it in turn | ||
| asks its `SessionSavingSceneAgent` to save its sessions if needed. | ||
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| Case (3) is handled by `SessionRestorationBrowserAgent` via WebState and | ||
| WebStateList observation. | ||
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| Case (4) is handled by the `PrerenderService`; it directly calls | ||
| `SaveSession()`, regardless of whether the session is in the background. | ||
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| Cases (3) and (4) save after a short delay, and repeated session saves within | ||
| that delay are ignored. Cases (1) and (2) save immediately (canceling any | ||
| pending delayed saves). `SessionServiceIOS` handles this. | ||
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| ### Session Restoration | ||
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| TODO: Describe when sessions are restored. | ||
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| ### Session Recovery | ||
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| TODO: Describe the logic for post-crash session recovery and how sessions are | ||
| set aside and (possibly) discarded. | ||
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| ### Incognito Sessions | ||
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| TODO: Describe how Incognito sessions are stored, and how it differs from how | ||
| regular session are. |
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| // Copyright 2021 The Chromium Authors. All rights reserved. | ||
| // Use of this source code is governed by a BSD-style license that can be | ||
| // found in the LICENSE file. | ||
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| #ifndef IOS_CHROME_BROWSER_SESSIONS_SESSION_SAVING_SCENE_AGENT_H_ | ||
| #define IOS_CHROME_BROWSER_SESSIONS_SESSION_SAVING_SCENE_AGENT_H_ | ||
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| #import <Foundation/Foundation.h> | ||
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| #import "ios/chrome/browser/ui/main/observing_scene_state_agent.h" | ||
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| @interface SessionSavingSceneAgent : ObservingSceneAgent | ||
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| // Saves the scene's sessions if they haven't been saved since the last time | ||
| // the scene was foregrounded. | ||
| - (void)saveSessionsIfNeeded; | ||
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| @end | ||
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| #endif // IOS_CHROME_BROWSER_SESSIONS_SESSION_SAVING_SCENE_AGENT_H_ |
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ios/chrome/browser/sessions/session_saving_scene_agent.mm
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| // Copyright 2021 The Chromium Authors. All rights reserved. | ||
| // Use of this source code is governed by a BSD-style license that can be | ||
| // found in the LICENSE file. | ||
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| #import "ios/chrome/browser/sessions/session_saving_scene_agent.h" | ||
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| #import "ios/chrome/browser/browser_state/chrome_browser_state.h" | ||
| #import "ios/chrome/browser/main/browser.h" | ||
| #import "ios/chrome/browser/sessions/session_restoration_browser_agent.h" | ||
| #import "ios/chrome/browser/snapshots/snapshot_tab_helper.h" | ||
| #import "ios/chrome/browser/ui/main/browser_interface_provider.h" | ||
| #import "ios/chrome/browser/web_state_list/web_state_list.h" | ||
| #import "ios/chrome/browser/web_state_list/web_usage_enabler/web_usage_enabler_browser_agent.h" | ||
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| #if !defined(__has_feature) || !__has_feature(objc_arc) | ||
| #error "This file requires ARC support." | ||
| #endif | ||
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| @implementation SessionSavingSceneAgent { | ||
| // YES when sessions need saving -- specifically after the scene has | ||
| // foregrounded. Initially NO, so session saving isn't triggered as the | ||
| // scene initially launches. | ||
| BOOL _sessionsNeedSaving; | ||
| } | ||
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| #pragma mark - SceneStateObserver | ||
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| - (void)sceneState:(SceneState*)sceneState | ||
| transitionedToActivationLevel:(SceneActivationLevel)level { | ||
| switch (level) { | ||
| case SceneActivationLevelUnattached: | ||
| // no-op. | ||
| break; | ||
| case SceneActivationLevelBackground: | ||
| [self saveSessionsIfNeeded]; | ||
| break; | ||
| case SceneActivationLevelForegroundInactive: | ||
| [self prepareSessionsForBackgrounding]; | ||
| break; | ||
| case SceneActivationLevelForegroundActive: | ||
| _sessionsNeedSaving = YES; | ||
| break; | ||
| } | ||
| } | ||
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| #pragma mark - Public | ||
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| - (void)saveSessionsIfNeeded { | ||
| // No need to do this if the session is already saved. | ||
| if (!_sessionsNeedSaving) | ||
| return; | ||
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| id<BrowserInterfaceProvider> interfaceProvider = | ||
| self.sceneState.interfaceProvider; | ||
| if (!interfaceProvider) | ||
| return; | ||
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| // Since the app is about to be backgrounded or terminated, save the sessions | ||
| // immediately. | ||
| Browser* mainBrowser = interfaceProvider.mainInterface.browser; | ||
| SessionRestorationBrowserAgent::FromBrowser(mainBrowser) | ||
| ->SaveSession(/*immediately=*/true); | ||
| if (interfaceProvider.hasIncognitoInterface) { | ||
| Browser* incognitoBrowser = interfaceProvider.incognitoInterface.browser; | ||
| SessionRestorationBrowserAgent::FromBrowser(incognitoBrowser) | ||
| ->SaveSession(/*immediately=*/true); | ||
| } | ||
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| // Save a grey version of the active webstates. | ||
| SnapshotTabHelper* mainSnapshotHelper = | ||
| [self snapshotHelperForActiveWebStateInMainBrowser]; | ||
| if (mainSnapshotHelper) { | ||
| mainSnapshotHelper->SaveGreyInBackground(); | ||
| } | ||
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| SnapshotTabHelper* incognitoSnapshotHelper = | ||
| [self snapshotHelperForActiveWebStateInIncognitoBrowser]; | ||
| if (incognitoSnapshotHelper) { | ||
| incognitoSnapshotHelper->SaveGreyInBackground(); | ||
| } | ||
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| _sessionsNeedSaving = NO; | ||
| } | ||
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| #pragma mark - Private | ||
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| - (void)prepareSessionsForBackgrounding { | ||
| SnapshotTabHelper* mainSnapshotHelper = | ||
| [self snapshotHelperForActiveWebStateInMainBrowser]; | ||
| if (mainSnapshotHelper) { | ||
| mainSnapshotHelper->WillBeSavedGreyWhenBackgrounding(); | ||
| } | ||
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| SnapshotTabHelper* incognitoSnapshotHelper = | ||
| [self snapshotHelperForActiveWebStateInIncognitoBrowser]; | ||
| if (incognitoSnapshotHelper) { | ||
| incognitoSnapshotHelper->WillBeSavedGreyWhenBackgrounding(); | ||
| } | ||
| } | ||
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| #pragma mark - Utility | ||
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| - (SnapshotTabHelper*)snapshotHelperForActiveWebStateInMainBrowser { | ||
| id<BrowserInterfaceProvider> interfaceProvider = | ||
| self.sceneState.interfaceProvider; | ||
| if (!interfaceProvider) | ||
| return nullptr; | ||
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| return [self | ||
| snapshotHelperForActiveWebStateInBrowser:interfaceProvider.mainInterface | ||
| .browser]; | ||
| } | ||
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| - (SnapshotTabHelper*)snapshotHelperForActiveWebStateInIncognitoBrowser { | ||
| id<BrowserInterfaceProvider> interfaceProvider = | ||
| self.sceneState.interfaceProvider; | ||
| if (!interfaceProvider.hasIncognitoInterface) | ||
| return nullptr; | ||
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| return [self | ||
| snapshotHelperForActiveWebStateInBrowser:interfaceProvider | ||
| .incognitoInterface.browser]; | ||
| } | ||
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| - (SnapshotTabHelper*)snapshotHelperForActiveWebStateInBrowser: | ||
| (Browser*)browser { | ||
| WebUsageEnablerBrowserAgent* webEnabler = | ||
| WebUsageEnablerBrowserAgent::FromBrowser(browser); | ||
| web::WebState* webState = browser->GetWebStateList()->GetActiveWebState(); | ||
| if (webEnabler->IsWebUsageEnabled() && webState != nullptr) { | ||
| return SnapshotTabHelper::FromWebState(webState); | ||
| } | ||
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| return nullptr; | ||
| } | ||
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| @end |
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