[5/N] WindowDecorViewHost: Add pooled supplier & reusable ViewHost

Spiritual revert^2 of I08111bfd4728e5223ed078916255313b13a4093f, but
broken down into smaller changes.

Adds a ReusableWindowDecorViewHost that is able to swap view hierarchies
(e.g. App Handle <-> App Header) without having to release and create a
new SCVH. This is done by putting the desired view hierarchy inside a
root View that never changes.
Also adds a Pooled supplier that uses reusable view hosts with a
capacity equal to the desktop task limit.

Bug: 360452034
Flag: com.android.window.flags.enable_desktop_windowing_scvh_cache_bug_fix
Test: check perfetto trace for reused SCVHs

Change-Id: I30555d86ec6995decbca8a47c1008f1b79020899

6 files changed, 508 insertions, 0 deletions

diff --git a/libs/WindowManager/Shell/shared/src/com/android/wm/shell/shared/desktopmode/DesktopModeStatus.java b/libs/WindowManager/Shell/shared/src/com/android/wm/shell/shared/desktopmode/DesktopModeStatus.java
index 04c17e54d11f..a5205ee24d05 100644
--- a/libs/WindowManager/Shell/shared/src/com/android/wm/shell/shared/desktopmode/DesktopModeStatus.java
+++ b/libs/WindowManager/Shell/shared/src/com/android/wm/shell/shared/desktopmode/DesktopModeStatus.java
@@ -162,6 +162,21 @@ public class DesktopModeStatus {
     }
 
     /**
+     * Return the maximum size of the window decoration surface control view host pool, or zero if
+     * there should be no pooling.
+     */
+    public static int getWindowDecorScvhPoolSize(@NonNull Context context) {
+        if (!Flags.enableDesktopWindowingScvhCacheBugFix()) return 0;
+        final int maxTaskLimit = getMaxTaskLimit(context);
+        if (maxTaskLimit > 0) {
+            return maxTaskLimit;
+        }
+        // TODO: b/368032552 - task limit equal to 0 means unlimited. Figure out what the pool
+        //  size should be in that case.
+        return 0;
+    }
+
+    /**
      * Return {@code true} if the current device supports desktop mode.
      */
     @VisibleForTesting
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java b/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java
index 86e0d08ba05a..f9e3be9c770f 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java
@@ -152,6 +152,7 @@ import com.android.wm.shell.windowdecor.DesktopModeWindowDecorViewModel;
 import com.android.wm.shell.windowdecor.WindowDecorViewModel;
 import com.android.wm.shell.windowdecor.additionalviewcontainer.AdditionalSystemViewContainer;
 import com.android.wm.shell.windowdecor.common.viewhost.DefaultWindowDecorViewHostSupplier;
+import com.android.wm.shell.windowdecor.common.viewhost.PooledWindowDecorViewHostSupplier;
 import com.android.wm.shell.windowdecor.common.viewhost.WindowDecorViewHost;
 import com.android.wm.shell.windowdecor.common.viewhost.WindowDecorViewHostSupplier;
 import com.android.wm.shell.windowdecor.education.DesktopWindowingEducationPromoController;
@@ -347,7 +348,12 @@ public abstract class WMShellModule {
     @WMSingleton
     @Provides
     static WindowDecorViewHostSupplier<WindowDecorViewHost> provideWindowDecorViewHostSupplier(
+            @NonNull Context context,
             @ShellMainThread @NonNull CoroutineScope mainScope) {
+        final int poolSize = DesktopModeStatus.getWindowDecorScvhPoolSize(context);
+        if (DesktopModeStatus.canEnterDesktopModeOrShowAppHandle(context) && poolSize > 0) {
+            return new PooledWindowDecorViewHostSupplier(mainScope, poolSize);
+        }
         return new DefaultWindowDecorViewHostSupplier(mainScope);
     }
 
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/common/viewhost/PooledWindowDecorViewHostSupplier.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/common/viewhost/PooledWindowDecorViewHostSupplier.kt
new file mode 100644
index 000000000000..adb0ba643e0d
--- /dev/null
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/common/viewhost/PooledWindowDecorViewHostSupplier.kt
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.wm.shell.windowdecor.common.viewhost
+
+import android.content.Context
+import android.os.Trace
+import android.util.Pools
+import android.view.Display
+import android.view.SurfaceControl
+import com.android.wm.shell.shared.annotations.ShellMainThread
+import kotlinx.coroutines.CoroutineScope
+
+/**
+ * A [WindowDecorViewHostSupplier] backed by a pool to allow recycling view hosts which may be
+ * expensive to recreate for each new or updated window decoration.
+ *
+ * Callers can obtain a [WindowDecorViewHost] using [acquire], which will return a pooled
+ * object if available, or create a new instance and return it if needed. When finished using a
+ * [WindowDecorViewHost], it must be released using [release] to allow it to be sent back
+ * into the pool and reused later on.
+ */
+class PooledWindowDecorViewHostSupplier(
+    @ShellMainThread private val mainScope: CoroutineScope,
+    maxPoolSize: Int,
+) : WindowDecorViewHostSupplier<WindowDecorViewHost> {
+
+    private val pool: Pools.Pool<WindowDecorViewHost> = Pools.SynchronizedPool(maxPoolSize)
+    private var nextDecorViewHostId = 0
+
+    override fun acquire(context: Context, display: Display): WindowDecorViewHost {
+        val pooledViewHost = pool.acquire()
+        if (pooledViewHost != null) {
+            return pooledViewHost
+        }
+        Trace.beginSection("PooledWindowDecorViewHostSupplier#acquire-newInstance")
+        val newDecorViewHost = newInstance(context, display)
+        Trace.endSection()
+        return newDecorViewHost
+    }
+
+    override fun release(viewHost: WindowDecorViewHost, t: SurfaceControl.Transaction) {
+        val pooled = pool.release(viewHost)
+        if (!pooled) {
+            viewHost.release(t)
+        }
+    }
+
+    private fun newInstance(context: Context, display: Display): ReusableWindowDecorViewHost {
+        // Use a reusable window decor view host, as it allows swapping the entire view hierarchy.
+        return ReusableWindowDecorViewHost(
+            context = context,
+            mainScope = mainScope,
+            display = display,
+            id = nextDecorViewHostId++
+        )
+    }
+}
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/common/viewhost/ReusableWindowDecorViewHost.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/common/viewhost/ReusableWindowDecorViewHost.kt
new file mode 100644
index 000000000000..bf0b1186254f
--- /dev/null
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/common/viewhost/ReusableWindowDecorViewHost.kt
@@ -0,0 +1,118 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.wm.shell.windowdecor.common.viewhost
+
+import android.content.Context
+import android.content.res.Configuration
+import android.graphics.Region
+import android.view.Display
+import android.view.SurfaceControl
+import android.view.View
+import android.view.WindowManager
+import android.widget.FrameLayout
+import androidx.tracing.Trace
+import com.android.internal.annotations.VisibleForTesting
+import com.android.wm.shell.shared.annotations.ShellMainThread
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.launch
+
+/**
+ * An implementation of [WindowDecorViewHost] that supports:
+ * 1) Replacing the root [View], meaning [WindowDecorViewHost.updateView] maybe be called with
+ *    different [View] instances. This is useful when reusing [WindowDecorViewHost]s instances for
+ *    vastly different view hierarchies, such as Desktop Windowing's App Handles and App Headers.
+ */
+class ReusableWindowDecorViewHost(
+    private val context: Context,
+    @ShellMainThread private val mainScope: CoroutineScope,
+    display: Display,
+    val id: Int,
+    @VisibleForTesting
+    val viewHostAdapter: SurfaceControlViewHostAdapter =
+        SurfaceControlViewHostAdapter(context, display),
+) : WindowDecorViewHost {
+    @VisibleForTesting val rootView = FrameLayout(context)
+
+    private var currentUpdateJob: Job? = null
+
+    override val surfaceControl: SurfaceControl
+        get() = viewHostAdapter.rootSurface
+
+    override fun updateView(
+        view: View,
+        attrs: WindowManager.LayoutParams,
+        configuration: Configuration,
+        touchableRegion: Region?,
+        onDrawTransaction: SurfaceControl.Transaction?,
+    ) {
+        Trace.beginSection("ReusableWindowDecorViewHost#updateView")
+        clearCurrentUpdateJob()
+        updateViewHost(view, attrs, configuration, touchableRegion, onDrawTransaction)
+        Trace.endSection()
+    }
+
+    override fun updateViewAsync(
+        view: View,
+        attrs: WindowManager.LayoutParams,
+        configuration: Configuration,
+        touchableRegion: Region?,
+    ) {
+        Trace.beginSection("ReusableWindowDecorViewHost#updateViewAsync")
+        clearCurrentUpdateJob()
+        currentUpdateJob =
+            mainScope.launch {
+                updateViewHost(
+                    view,
+                    attrs,
+                    configuration,
+                    touchableRegion,
+                    onDrawTransaction = null,
+                )
+            }
+        Trace.endSection()
+    }
+
+    override fun release(t: SurfaceControl.Transaction) {
+        clearCurrentUpdateJob()
+        viewHostAdapter.release(t)
+    }
+
+    private fun updateViewHost(
+        view: View,
+        attrs: WindowManager.LayoutParams,
+        configuration: Configuration,
+        touchableRegion: Region?,
+        onDrawTransaction: SurfaceControl.Transaction?,
+    ) {
+        Trace.beginSection("ReusableWindowDecorViewHost#updateViewHost")
+        viewHostAdapter.prepareViewHost(configuration, touchableRegion)
+        onDrawTransaction?.let { viewHostAdapter.applyTransactionOnDraw(it) }
+        rootView.removeAllViews()
+        rootView.addView(view)
+        viewHostAdapter.updateView(rootView, attrs)
+        Trace.endSection()
+    }
+
+    private fun clearCurrentUpdateJob() {
+        currentUpdateJob?.cancel()
+        currentUpdateJob = null
+    }
+
+    companion object {
+        private const val TAG = "ReusableWindowDecorViewHost"
+    }
+}
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/windowdecor/common/viewhost/PooledWindowDecorViewHostSupplierTest.kt b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/windowdecor/common/viewhost/PooledWindowDecorViewHostSupplierTest.kt
new file mode 100644
index 000000000000..40583f80003c
--- /dev/null
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/windowdecor/common/viewhost/PooledWindowDecorViewHostSupplierTest.kt
@@ -0,0 +1,129 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.wm.shell.windowdecor.common.viewhost
+
+import android.content.res.Configuration
+import android.graphics.Region
+import android.testing.AndroidTestingRunner
+import android.view.SurfaceControl
+import android.view.View
+import android.view.WindowManager
+import androidx.test.filters.SmallTest
+import com.android.wm.shell.ShellTestCase
+import com.android.wm.shell.util.StubTransaction
+import com.google.common.truth.Truth.assertThat
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.test.runTest
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.MockitoAnnotations
+import org.mockito.kotlin.mock
+
+/**
+ * Tests for [PooledWindowDecorViewHostSupplier].
+ *
+ * Build/Install/Run: atest WMShellUnitTests:PooledWindowDecorViewHostSupplierTest
+ */
+@SmallTest
+@RunWith(AndroidTestingRunner::class)
+class PooledWindowDecorViewHostSupplierTest : ShellTestCase() {
+
+    private lateinit var supplier: PooledWindowDecorViewHostSupplier
+
+    @Test
+    fun setUp() {
+        MockitoAnnotations.initMocks(this)
+    }
+
+    @Test
+    fun acquire_poolBelowLimit_caches() = runTest {
+        supplier = createSupplier(maxPoolSize = 5)
+
+        val viewHost = FakeWindowDecorViewHost()
+        supplier.release(viewHost, StubTransaction())
+
+        assertThat(supplier.acquire(context, context.display)).isEqualTo(viewHost)
+    }
+
+    @Test
+    fun release_poolBelowLimit_doesNotReleaseViewHost() = runTest {
+        supplier = createSupplier(maxPoolSize = 5)
+
+        val viewHost = FakeWindowDecorViewHost()
+        val mockT = mock<SurfaceControl.Transaction>()
+        supplier.release(viewHost, mockT)
+
+        assertThat(viewHost.released).isFalse()
+    }
+
+    @Test
+    fun release_poolAtLimit_doesNotCache() = runTest {
+        supplier = createSupplier(maxPoolSize = 1)
+        val viewHost = FakeWindowDecorViewHost()
+        supplier.release(viewHost, StubTransaction()) // Maxes pool.
+
+        val viewHost2 = FakeWindowDecorViewHost()
+        supplier.release(viewHost2, StubTransaction()) // Beyond limit.
+
+        assertThat(supplier.acquire(context, context.display)).isEqualTo(viewHost)
+        // Second one wasn't cached, so the acquired one should've been a new instance.
+        assertThat(supplier.acquire(context, context.display)).isNotEqualTo(viewHost2)
+    }
+
+    @Test
+    fun release_poolAtLimit_releasesViewHost() = runTest {
+        supplier = createSupplier(maxPoolSize = 1)
+        val viewHost = FakeWindowDecorViewHost()
+        supplier.release(viewHost, StubTransaction()) // Maxes pool.
+
+        val viewHost2 = FakeWindowDecorViewHost()
+        val mockT = mock<SurfaceControl.Transaction>()
+        supplier.release(viewHost2, mockT) // Beyond limit.
+
+        // Second one doesn't fit, so it needs to be released.
+        assertThat(viewHost2.released).isTrue()
+    }
+
+    private fun CoroutineScope.createSupplier(maxPoolSize: Int) =
+        PooledWindowDecorViewHostSupplier(this, maxPoolSize)
+
+    private class FakeWindowDecorViewHost : WindowDecorViewHost {
+        var released = false
+            private set
+
+        override val surfaceControl: SurfaceControl
+            get() = SurfaceControl()
+
+        override fun updateView(
+            view: View,
+            attrs: WindowManager.LayoutParams,
+            configuration: Configuration,
+            touchableRegion: Region?,
+            onDrawTransaction: SurfaceControl.Transaction?,
+        ) {}
+
+        override fun updateViewAsync(
+            view: View,
+            attrs: WindowManager.LayoutParams,
+            configuration: Configuration,
+            touchableRegion: Region?,
+        ) {}
+
+        override fun release(t: SurfaceControl.Transaction) {
+            released = true
+        }
+    }
+}
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/windowdecor/common/viewhost/ReusableWindowDecorViewHostTest.kt b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/windowdecor/common/viewhost/ReusableWindowDecorViewHostTest.kt
new file mode 100644
index 000000000000..245393a6d44e
--- /dev/null
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/windowdecor/common/viewhost/ReusableWindowDecorViewHostTest.kt
@@ -0,0 +1,170 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.wm.shell.windowdecor.common.viewhost
+
+import android.testing.AndroidTestingRunner
+import android.testing.TestableLooper
+import android.view.SurfaceControl
+import android.view.View
+import android.view.WindowManager
+import androidx.test.filters.SmallTest
+import com.android.wm.shell.ShellTestCase
+import com.google.common.truth.Truth.assertThat
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.runTest
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.Mockito.mock
+import org.mockito.kotlin.spy
+import org.mockito.kotlin.verify
+
+/**
+ * Tests for [ReusableWindowDecorViewHost].
+ *
+ * Build/Install/Run: atest WMShellUnitTests:ReusableWindowDecorViewHostTest
+ */
+@SmallTest
+@TestableLooper.RunWithLooper
+@RunWith(AndroidTestingRunner::class)
+class ReusableWindowDecorViewHostTest : ShellTestCase() {
+
+    @Test
+    fun update_differentView_replacesView() = runTest {
+        val view = View(context)
+        val lp = WindowManager.LayoutParams()
+        val reusableVH = createReusableViewHost()
+        reusableVH.updateView(view, lp, context.resources.configuration, null)
+
+        assertThat(reusableVH.rootView.childCount).isEqualTo(1)
+        assertThat(reusableVH.rootView.getChildAt(0)).isEqualTo(view)
+
+        val newView = View(context)
+        val newLp = WindowManager.LayoutParams()
+        reusableVH.updateView(newView, newLp, context.resources.configuration, null)
+
+        assertThat(reusableVH.rootView.childCount).isEqualTo(1)
+        assertThat(reusableVH.rootView.getChildAt(0)).isEqualTo(newView)
+    }
+
+    @OptIn(ExperimentalCoroutinesApi::class)
+    @Test
+    fun updateView_clearsPendingAsyncJob() = runTest {
+        val reusableVH = createReusableViewHost()
+        val asyncView = View(context)
+        val syncView = View(context)
+        val asyncAttrs = WindowManager.LayoutParams(100, 100)
+        val syncAttrs = WindowManager.LayoutParams(200, 200)
+
+        reusableVH.updateViewAsync(
+            view = asyncView,
+            attrs = asyncAttrs,
+            configuration = context.resources.configuration,
+        )
+
+        // No view host yet, since the coroutine hasn't run.
+        assertThat(reusableVH.viewHostAdapter.isInitialized()).isFalse()
+
+        reusableVH.updateView(
+            view = syncView,
+            attrs = syncAttrs,
+            configuration = context.resources.configuration,
+            onDrawTransaction = null,
+        )
+
+        // Would run coroutine if it hadn't been cancelled.
+        advanceUntilIdle()
+
+        assertThat(reusableVH.viewHostAdapter.isInitialized()).isTrue()
+        // View host view/attrs should match the ones from the sync call.
+        assertThat(reusableVH.rootView.getChildAt(0)).isEqualTo(syncView)
+        assertThat(reusableVH.view()!!.layoutParams.width).isEqualTo(syncAttrs.width)
+    }
+
+    @OptIn(ExperimentalCoroutinesApi::class)
+    @Test
+    fun updateViewAsync() = runTest {
+        val reusableVH = createReusableViewHost()
+        val view = View(context)
+        val attrs = WindowManager.LayoutParams(100, 100)
+
+        reusableVH.updateViewAsync(
+            view = view,
+            attrs = attrs,
+            configuration = context.resources.configuration,
+        )
+
+        assertThat(reusableVH.viewHostAdapter.isInitialized()).isFalse()
+
+        advanceUntilIdle()
+
+        assertThat(reusableVH.viewHostAdapter.isInitialized()).isTrue()
+    }
+
+    @OptIn(ExperimentalCoroutinesApi::class)
+    @Test
+    fun updateViewAsync_clearsPendingAsyncJob() = runTest {
+        val reusableVH = createReusableViewHost()
+
+        val view = View(context)
+        reusableVH.updateViewAsync(
+            view = view,
+            attrs = WindowManager.LayoutParams(100, 100),
+            configuration = context.resources.configuration,
+        )
+        val otherView = View(context)
+        reusableVH.updateViewAsync(
+            view = otherView,
+            attrs = WindowManager.LayoutParams(100, 100),
+            configuration = context.resources.configuration,
+        )
+
+        advanceUntilIdle()
+
+        assertThat(reusableVH.viewHostAdapter.isInitialized()).isTrue()
+        assertThat(reusableVH.rootView.getChildAt(0)).isEqualTo(otherView)
+    }
+
+    @Test
+    fun release() = runTest {
+        val reusableVH = createReusableViewHost()
+
+        val view = View(context)
+        reusableVH.updateView(
+            view = view,
+            attrs = WindowManager.LayoutParams(100, 100),
+            configuration = context.resources.configuration,
+            onDrawTransaction = null,
+        )
+
+        val t = mock(SurfaceControl.Transaction::class.java)
+        reusableVH.release(t)
+
+        verify(reusableVH.viewHostAdapter).release(t)
+    }
+
+    private fun CoroutineScope.createReusableViewHost() =
+        ReusableWindowDecorViewHost(
+            context = context,
+            mainScope = this,
+            display = context.display,
+            id = 1,
+            viewHostAdapter = spy(SurfaceControlViewHostAdapter(context, context.display)),
+        )
+
+    private fun ReusableWindowDecorViewHost.view(): View? = viewHostAdapter.viewHost?.view
+}