Closes #3639: browser-state: Add onLowMemory behavior

components/browser/session/src/main/java/mozilla/components/browser/session/SessionManager.kt

@@ -8,6 +8,7 @@ import mozilla.components.browser.session.ext.syncDispatch
 import mozilla.components.browser.session.ext.toCustomTabSessionState
 import mozilla.components.browser.session.ext.toTabSessionState
 import mozilla.components.browser.state.action.CustomTabListAction
+import mozilla.components.browser.state.action.SystemAction
 import mozilla.components.browser.state.action.TabListAction
 import mozilla.components.browser.state.store.BrowserStore
 import mozilla.components.concept.engine.Engine
@@ -227,7 +228,10 @@ class SessionManager(
      * Informs this [SessionManager] that the OS is in low memory condition so it
      * can reduce its allocated objects.
      */
-    fun onLowMemory() = delegate.onLowMemory()
+    fun onLowMemory() {
+        delegate.onLowMemory()
+        store?.syncDispatch(SystemAction.LowMemoryAction)
+    }
 
     companion object {
         const val NO_SELECTION = -1

components/browser/session/src/main/java/mozilla/components/browser/session/ext/SessionExtensions.kt

@@ -32,7 +32,8 @@ private fun Session.toContentState(): ContentState {
         progress,
         loading,
         searchTerms,
-        securityInfo.toSecurityInfoState()
+        securityInfo.toSecurityInfoState(),
+        thumbnail
     )
 }
 

components/browser/session/src/test/java/mozilla/components/browser/session/SessionManagerMigrationTest.kt

@@ -451,4 +451,31 @@ class SessionManagerMigrationTest {
             }
         }
     }
+
+    @Test
+    fun `thumbnails of all but selected session should be removed on low memory`() {
+        val store = BrowserStore()
+        val sessionManager = SessionManager(engine = mock(), store = store)
+
+        val session1 = Session("https://www.mozilla.org")
+        val session2 = Session("https://getpocket.com")
+        val session3 = Session("https://www.firefox.com")
+
+        sessionManager.add(session1, false)
+        session1.thumbnail = mock()
+        sessionManager.add(session2, false)
+        session2.thumbnail = mock()
+        sessionManager.add(session3, true)
+        session3.thumbnail = mock()
+
+        val allSessionsMustHaveAThumbnail = store.state.tabs.all { it.content.thumbnail != null }
+        assertTrue(allSessionsMustHaveAThumbnail)
+
+        sessionManager.onLowMemory()
+
+        assertNull(store.state.tabs[0].content.thumbnail)
+        assertNull(store.state.tabs[1].content.thumbnail)
+        // Thumbnail of selected session should not have been removed
+        assertNotNull(store.state.tabs[2].content.thumbnail)
+    }
 }

components/browser/session/src/test/java/mozilla/components/browser/session/SessionManagerTest.kt

@@ -668,7 +668,7 @@ class SessionManagerTest {
     }
 
     @Test
-    fun `all not selected sessions should be removed on Low Memory`() {
+    fun `thumbnails of all but selected session should be removed on low memory`() {
         val manager = SessionManager(mock())
 
         val emptyBitmap = spy(Bitmap::class.java)

components/browser/state/src/main/java/mozilla/components/browser/state/action/BrowserAction.kt

@@ -18,6 +18,17 @@ import mozilla.components.lib.state.Action
  */
 sealed class BrowserAction : Action
 
+/**
+ * [BrowserAction] implementations to react to system events.
+ */
+sealed class SystemAction : BrowserAction() {
+    /**
+     * Optimizes the [BrowserState] by removing unneeded and optional
+     * resources if the system is in a low memory condition.
+     */
+    object LowMemoryAction : SystemAction()
+}
+
 /**
  * [BrowserAction] implementations related to updating the list of [TabSessionState] inside [BrowserState].
  */

components/browser/state/src/main/java/mozilla/components/browser/state/reducer/BrowserStateReducer.kt

@@ -7,6 +7,7 @@ package mozilla.components.browser.state.reducer
 import mozilla.components.browser.state.action.BrowserAction
 import mozilla.components.browser.state.action.ContentAction
 import mozilla.components.browser.state.action.CustomTabListAction
+import mozilla.components.browser.state.action.SystemAction
 import mozilla.components.browser.state.action.TabListAction
 import mozilla.components.browser.state.state.BrowserState
 import mozilla.components.browser.state.store.BrowserStore
@@ -21,9 +22,10 @@ import mozilla.components.lib.state.Action
 internal object BrowserStateReducer {
     fun reduce(state: BrowserState, action: BrowserAction): BrowserState {
         return when (action) {
-            is TabListAction -> TabListReducer.reduce(state, action)
-            is CustomTabListAction -> CustomTabListReducer.reduce(state, action)
             is ContentAction -> ContentStateReducer.reduce(state, action)
+            is CustomTabListAction -> CustomTabListReducer.reduce(state, action)
+            is SystemAction -> SystemReducer.reduce(state, action)
+            is TabListAction -> TabListReducer.reduce(state, action)
         }
     }
 }

components/browser/state/src/main/java/mozilla/components/browser/state/reducer/SystemReducer.kt

+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package mozilla.components.browser.state.reducer
+
+import mozilla.components.browser.state.action.SystemAction
+import mozilla.components.browser.state.state.BrowserState
+
+internal object SystemReducer {
+    /**
+     * [SystemAction] Reducer function for modifying [BrowserState].
+     */
+    fun reduce(state: BrowserState, action: SystemAction): BrowserState {
+        return when (action) {
+            is SystemAction.LowMemoryAction -> {
+                val updatedTabs = state.tabs.map {
+                    if (state.selectedTabId != it.id) {
+                        it.copy(content = it.content.copy(thumbnail = null))
+                    } else {
+                        it
+                    }
+                }
+                state.copy(tabs = updatedTabs)
+            }
+        }
+    }
+}

components/browser/state/src/test/java/mozilla/components/browser/state/action/SystemActionTest.kt

+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package mozilla.components.browser.state.action
+
+import mozilla.components.browser.state.state.BrowserState
+import mozilla.components.browser.state.state.createTab
+import mozilla.components.browser.state.store.BrowserStore
+import mozilla.components.support.test.ext.joinBlocking
+import mozilla.components.support.test.mock
+import org.junit.Assert.assertNotNull
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+class SystemActionTest {
+
+    @Test
+    fun `LowMemoryAction removes thumbnails`() {
+        val initialState = BrowserState(tabs = listOf(
+            createTab(url = "https://www.mozilla.org", id = "0"),
+            createTab(url = "https://www.firefox.com", id = "1"),
+            createTab(url = "https://www.firefox.com", id = "2")
+        ))
+        val store = BrowserStore(initialState)
+
+        store.dispatch(ContentAction.UpdateThumbnailAction("0", mock())).joinBlocking()
+        store.dispatch(ContentAction.UpdateThumbnailAction("1", mock())).joinBlocking()
+        store.dispatch(ContentAction.UpdateThumbnailAction("2", mock())).joinBlocking()
+        store.dispatch(TabListAction.SelectTabAction(tabId = "2")).joinBlocking()
+        assertNotNull(store.state.tabs[0].content.thumbnail)
+        assertNotNull(store.state.tabs[1].content.thumbnail)
+        assertNotNull(store.state.tabs[2].content.thumbnail)
+
+        store.dispatch(SystemAction.LowMemoryAction).joinBlocking()
+        assertNull(store.state.tabs[0].content.thumbnail)
+        assertNull(store.state.tabs[1].content.thumbnail)
+        // Thumbnail of selected tab should not have been removed
+        assertNotNull(store.state.tabs[2].content.thumbnail)
+    }
+}