Single bitmap pool with view size changes support

Summary:
This change aims to reduce the number of bitmap pools by definiting a default pool which can contain bitmaps of different sizes.

A side benefit is that this single pool facilitates handling the case where a view gets resized too.

So overall, this should be both more generic and efficient compared to the previous approach.

Reviewed By: LukeDefeo

Differential Revision: D39815821

fbshipit-source-id: e0aa17ba55db07b74d8f22ea16e0c864288fb169

android/src/main/java/com/facebook/flipper/plugins/uidebugger/UIDebuggerFlipperPlugin.kt

@@ -45,6 +45,7 @@ class UIDebuggerFlipperPlugin(
   override fun onConnect(connection: FlipperConnection) {
     Log.i(LogTag, "Connected")
     this.context.connectionRef.connection = connection
+    this.context.bitmapPool.makeReady()
 
     connection.send(
         InitEvent.name,
@@ -59,6 +60,7 @@ class UIDebuggerFlipperPlugin(
     Log.i(LogTag, "Disconnected")
 
     context.treeObserverManager.stop()
+    context.bitmapPool.recycleAll()
   }
 
   override fun runInBackground(): Boolean {

android/src/main/java/com/facebook/flipper/plugins/uidebugger/common/BitmapPool.kt

@@ -11,42 +11,58 @@ import android.graphics.Bitmap
 import android.os.Handler
 import android.os.Looper
 
-class BitmapPool(
-    private val width: Int,
-    private val height: Int,
-    private val config: Bitmap.Config = Bitmap.Config.RGB_565
-) {
+/** BitmapPool is intended to be used on the main thread. In other words, it is not thread-safe. */
+class BitmapPool(private val config: Bitmap.Config = Bitmap.Config.RGB_565) {
 
-  interface RecyclableBitmap {
+  interface ReusableBitmap {
     val bitmap: Bitmap?
-    fun recycle()
+    fun readyForReuse()
   }
 
   private var handler: Handler = Handler(Looper.getMainLooper())
 
-  private val bitmaps: MutableList<Bitmap> = mutableListOf()
+  private val container: MutableMap<String, MutableList<Bitmap>> = mutableMapOf()
   private var isRecycled = false
 
-  fun recycle() {
+  private fun generateKey(width: Int, height: Int): String = "$width,$height"
+
+  fun recycleAll() {
     isRecycled = true
+    container.forEach { (_, bitmaps) ->
       bitmaps.forEach { bitmap -> bitmap.recycle() }
       bitmaps.clear()
     }
 
-  fun getBitmap(): RecyclableBitmap {
-    return if (bitmaps.isEmpty()) {
+    container.clear()
+  }
+
+  fun makeReady() {
+    isRecycled = false
+  }
+
+  fun getBitmap(width: Int, height: Int): ReusableBitmap {
+    val key = generateKey(width, height)
+    val bitmaps = container[key]
+
+    return if (bitmaps == null || bitmaps.isEmpty()) {
       LeasedBitmap(Bitmap.createBitmap(width, height, config))
     } else {
       LeasedBitmap(bitmaps.removeLast())
     }
   }
 
-  inner class LeasedBitmap(override val bitmap: Bitmap) : RecyclableBitmap {
-    override fun recycle() {
+  inner class LeasedBitmap(override val bitmap: Bitmap) : ReusableBitmap {
+    override fun readyForReuse() {
+      val key = generateKey(bitmap.width, bitmap.height)
       handler.post {
         if (isRecycled) {
           bitmap.recycle()
         } else {
+          var bitmaps = container[key]
+          if (bitmaps == null) {
+            bitmaps = mutableListOf()
+            container[key] = bitmaps
+          }
           bitmaps.add(bitmap)
         }
       }
@@ -54,10 +70,6 @@ class BitmapPool(
   }
 
   companion object {
-    fun createBitmap(width: Int, height: Int, config: Bitmap.Config): Bitmap {
-      return Bitmap.createBitmap(width, height, config)
-    }
-
     fun createBitmapWithDefaultConfig(width: Int, height: Int): Bitmap {
       return Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565)
     }

android/src/main/java/com/facebook/flipper/plugins/uidebugger/core/Context.kt

@@ -8,6 +8,7 @@
 package com.facebook.flipper.plugins.uidebugger.core
 
 import com.facebook.flipper.core.FlipperConnection
+import com.facebook.flipper.plugins.uidebugger.common.BitmapPool
 import com.facebook.flipper.plugins.uidebugger.descriptors.DescriptorRegister
 import com.facebook.flipper.plugins.uidebugger.observers.TreeObserverFactory
 import com.facebook.flipper.plugins.uidebugger.observers.TreeObserverManager
@@ -23,6 +24,8 @@ data class Context(
       PartialLayoutTraversal(descriptorRegister, observerFactory)
 
   val treeObserverManager = TreeObserverManager(this)
+
+  val bitmapPool = BitmapPool()
 }
 
 data class ConnectionRef(var connection: FlipperConnection?)

android/src/main/java/com/facebook/flipper/plugins/uidebugger/observers/DecorViewTreeObserver.kt

@@ -40,10 +40,13 @@ class DecorViewObserver(val context: Context) : TreeObserver<DecorView>() {
 
     val throttledUpdate =
         throttleLatest<WeakReference<View>?>(throttleTimeMs, waitScope, mainScope) { weakView ->
-          if (node.width > 0 && node.height > 0) {
-            bitmapPool = BitmapPool(node.width, node.height)
+          weakView?.get()?.let { view ->
+            var snapshotBitmap: BitmapPool.ReusableBitmap? = null
+            if (view.width > 0 && view.height > 0) {
+              snapshotBitmap = context.bitmapPool.getBitmap(node.width, node.height)
+            }
+            processUpdate(context, view, snapshotBitmap)
           }
-          weakView?.get()?.let { view -> processUpdateWithSnapshot(context, view) }
         }
 
     listener =
@@ -68,9 +71,6 @@ class DecorViewObserver(val context: Context) : TreeObserver<DecorView>() {
     }
 
     nodeRef = null
-
-    bitmapPool?.recycle()
-    bitmapPool = null
   }
 }
 

android/src/main/java/com/facebook/flipper/plugins/uidebugger/observers/TreeObserver.kt

@@ -31,7 +31,6 @@ import com.facebook.flipper.plugins.uidebugger.descriptors.nodeId
 abstract class TreeObserver<T> {
 
   protected val children: MutableMap<Int, TreeObserver<*>> = mutableMapOf()
-  protected var bitmapPool: BitmapPool? = null
 
   abstract val type: String
 
@@ -39,12 +38,12 @@ abstract class TreeObserver<T> {
 
   abstract fun unsubscribe()
 
-  fun processUpdate(context: Context, root: Any) = this.processUpdate(context, root, false)
-  fun processUpdateWithSnapshot(context: Context, root: Any) =
-      this.processUpdate(context, root, true)
-
   /** Traverses the layout hierarchy while managing any encountered child observers. */
-  fun processUpdate(context: Context, root: Any, takeSnapshot: Boolean) {
+  fun processUpdate(
+      context: Context,
+      root: Any,
+      snapshotBitmap: BitmapPool.ReusableBitmap? = null
+  ) {
     val startTimestamp = System.currentTimeMillis()
     val (visitedNodes, observableRoots) = context.layoutTraversal.traverse(root)
 
@@ -82,20 +81,18 @@ abstract class TreeObserver<T> {
 
     Log.d(LogTag, "For Observer ${this.type} Sending ${visitedNodes.size}")
 
-    var recyclableBitmap: BitmapPool.RecyclableBitmap? = null
-    if (takeSnapshot && bitmapPool != null) {
+    if (snapshotBitmap != null) {
       @Suppress("unchecked_cast")
       val descriptor =
           context.descriptorRegister.descriptorForClassUnsafe(root::class.java)
               as NodeDescriptor<Any>
-      recyclableBitmap = bitmapPool?.getBitmap()
-      descriptor.getSnapshot(root, recyclableBitmap?.bitmap)
+      descriptor.getSnapshot(root, snapshotBitmap.bitmap)
     }
 
     val endTimestamp = System.currentTimeMillis()
     context.treeObserverManager.enqueueUpdate(
         SubtreeUpdate(
-            type, root.nodeId(), visitedNodes, startTimestamp, endTimestamp, recyclableBitmap))
+            type, root.nodeId(), visitedNodes, startTimestamp, endTimestamp, snapshotBitmap))
   }
 
   fun cleanUpRecursive() {

android/src/main/java/com/facebook/flipper/plugins/uidebugger/observers/TreeObserverManager.kt

@@ -31,7 +31,7 @@ data class SubtreeUpdate(
     val nodes: List<Node>,
     val startTime: Long,
     val traversalCompleteTime: Long,
-    val snapshot: BitmapPool.RecyclableBitmap?
+    val snapshot: BitmapPool.ReusableBitmap?
 )
 
 /** Holds the root observer and manages sending updates to desktop */
@@ -87,7 +87,7 @@ class TreeObserverManager(val context: Context) {
                             treeUpdate.nodes,
                             snapshot))
 
-                treeUpdate.snapshot.recycle()
+                treeUpdate.snapshot.readyForReuse()
               }
 
               val serializationEnd = System.currentTimeMillis()