Bitmap pool

Summary:
Bitmaps are not cheap to create. Also, bitmaps are used from the main thread to capture the contents of a view but can be used and processed by background threads.

BitmapPool aims to solve both problems.

- It is a pool that can be used to recycle bitmaps.
- The recyclable bitmap can be processed by a background thread which can explicitly recycle the bitmap once done with it, hence putting it back into the pool.

UPDATE: D39815821

That diff changes the approach by defining a single default pool which can handle bitmaps of different sizes.

Reviewed By: LukeDefeo

Differential Revision: D39812212

fbshipit-source-id: 065eea656f4139aeb9d09cd5a5c7dddfc9c8edfd

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

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.flipper.plugins.uidebugger.common
+
+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
+) {
+
+  interface RecyclableBitmap {
+    val bitmap: Bitmap?
+    fun recycle()
+  }
+
+  private var handler: Handler = Handler(Looper.getMainLooper())
+
+  private val bitmaps: MutableList<Bitmap> = mutableListOf()
+  private var isRecycled = false
+
+  fun recycle() {
+    isRecycled = true
+    bitmaps.forEach { bitmap -> bitmap.recycle() }
+    bitmaps.clear()
+  }
+
+  fun getBitmap(): RecyclableBitmap {
+    return if (bitmaps.isEmpty()) {
+      LeasedBitmap(Bitmap.createBitmap(width, height, config))
+    } else {
+      LeasedBitmap(bitmaps.removeLast())
+    }
+  }
+
+  inner class LeasedBitmap(override val bitmap: Bitmap) : RecyclableBitmap {
+    override fun recycle() {
+      handler.post {
+        if (isRecycled) {
+          bitmap.recycle()
+        } else {
+          bitmaps.add(bitmap)
+        }
+      }
+    }
+  }
+
+  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)
+    }
+  }
+}