Fix valgrind test failure for async read (#9819)

Summary:
Since all plaftorms don't support io_uring. So updated the unit
test to take that into consideration when testing async reads in unit tests.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9819

Test Plan:
valgrind --error-exitcode=2 --leak-check=full ./prefetch_test
--gtest_filter=PrefetchTest2.ReadAsyncWithPosixFS
CircleCI jobs

Reviewed By: pdillinger

Differential Revision: D35469959

Pulled By: akankshamahajan15

fbshipit-source-id: b170459ec816487fc0a13b1d55dbbe4f754b2eba

file/prefetch_test.cc

@@ -1099,8 +1099,12 @@ TEST_F(PrefetchTest2, ReadAsyncWithPosixFS) {
   }
 
   int buff_prefetch_count = 0;
+  bool read_async_called = false;
   SyncPoint::GetInstance()->SetCallBack("FilePrefetchBuffer::Prefetch:Start",
                                         [&](void*) { buff_prefetch_count++; });
+  ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->SetCallBack(
+      "UpdateResults::io_uring_result",
+      [&](void* /*arg*/) { read_async_called = true; });
   ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->EnableProcessing();
 
   // Read the keys.
@@ -1123,11 +1127,13 @@ TEST_F(PrefetchTest2, ReadAsyncWithPosixFS) {
     {
       HistogramData async_read_bytes;
       options.statistics->histogramData(ASYNC_READ_BYTES, &async_read_bytes);
-#if defined(ROCKSDB_IOURING_PRESENT)
+      // Not all platforms support iouring. In that case, ReadAsync in posix
+      // won't submit async requests.
+      if (read_async_called) {
         ASSERT_GT(async_read_bytes.count, 0);
-#else
+      } else {
         ASSERT_EQ(async_read_bytes.count, 0);
-#endif
+      }
     }
   }