Fix a bug in poll(from)

Test: new test in this patch
Flag: EXEMPT test-only
Change-Id: I00d367ce9db47e3fd30d27816b68280ab418f988

staticlibs/tests/unit/src/com/android/net/module/util/TrackRecordTest.kt

@@ -184,6 +184,25 @@ class TrackRecordTest {
         assertTrue(delay >= SHORT_TIMEOUT)
     }
 
+    @Test
+    fun testPollFrom() {
+        val readHead = ArrayTrackRecord<Int>().newReadHead()
+        readHead.add(3)
+        readHead.add(6)
+        readHead.add(7)
+        readHead.add(10)
+        assertEquals(0, readHead.mark)
+        assertEquals(3, readHead.poll(timeoutMs = 1, pos = 0) { it == 3 })
+        assertEquals(1, readHead.mark)
+        assertEquals(7, readHead.poll(timeoutMs = 1, pos = 0) { it == 7 })
+        assertEquals(3, readHead.mark)
+        // Do not advance the read head since the found element is after the current head
+        assertEquals(6, readHead.poll(timeoutMs = 1, pos = 0) { it == 6 })
+        assertEquals(3, readHead.mark)
+        assertNull(readHead.poll(timeoutMs = 1, pos = 1) { it == 3 })
+        assertEquals(4, readHead.mark)
+    }
+
     @Test
     fun testConcurrentPollDisallowed() {
         val failures = AtomicInteger(0)

staticlibs/testutils/hostdevice/com/android/net/module/util/TrackRecord.kt

@@ -315,7 +315,7 @@ class ArrayTrackRecord<E> : TrackRecord<E> {
                     val index = pollForIndexReadLocked(timeoutMs, pos, predicate)
                     when {
                         index < 0 -> readHead = size
-                        index > readHead -> readHead = index + 1
+                        index >= readHead -> readHead = index + 1
                         // else do nothing, the element was found prior to the read head so
                         // don't move the read head
                     }