fix: FramePool keeps undersized frames instead of discarding them

obtain() looks at each pooled frame of the size class at most once and
puts undersized ones back, so a smaller buffer in front of a suitable
one no longer causes an allocation and a lost buffer.

Author: compot-dev

android/app/src/main/java/com/openipc/decoder/FramePool.java

@@ -30,11 +30,16 @@ class FramePool {
     }
 
     Frame obtain(int size) {
-        boolean isSmall = size <= SMALL_MAX;
-        Frame frame = (isSmall ? small : large).poll();
-        if (frame != null && frame.data().length >= size) {
-            frame.setLength(0);
-            return frame;
+        BlockingQueue<Frame> queue = size <= SMALL_MAX ? small : large;
+        // Look at each pooled frame at most once; undersized ones go back for later requests
+        for (int i = queue.size(); i > 0; i--) {
+            Frame frame = queue.poll();
+            if (frame == null) break;
+            if (frame.data().length >= size) {
+                frame.setLength(0);
+                return frame;
+            }
+            queue.offer(frame);
         }
         // Round the capacity up so that the frame can be reused for similar sizes
         return new Frame(new byte[capacityFor(size)], 0);

android/app/src/test/java/com/openipc/decoder/FramePoolTest.java

@@ -56,4 +56,16 @@ public void largeClassIsBounded() {
         assertSame(f[1], pool.obtain(300_000));
         assertNotSame(f[2], pool.obtain(300_000)); // the third was dropped, not retained
     }
+
+    @Test
+    public void undersizedFramesAreKeptNotDiscarded() {
+        FramePool pool = new FramePool(8);
+        Frame small = pool.obtain(1000);   // 2 KiB
+        Frame bigger = pool.obtain(10_000); // 16 KiB
+        pool.recycle(small);
+        pool.recycle(bigger);
+        // A 10 KB request skips the 2 KiB frame without losing it
+        assertSame(bigger, pool.obtain(10_000));
+        assertSame(small, pool.obtain(1000));
+    }
 }