@Test
  public void cannotReadOnceClosed() throws IOException, InterruptedException, ExecutionException {
    final File path = tmp.newFile();
    final Env<ByteBuffer> env = create()
            .setMaxReaders(5)
            .open(path, MDB_NOSUBDIR);

    final Dbi<ByteBuffer> dbi = env.openDbi(DB_1, MDB_CREATE);

    dbi.put(bb(1), bb(10));
    dbi.put(bb(2), bb(20));

    try (Txn<ByteBuffer> roTxn = env.txnRead()) {
      assertThat(dbi.get(roTxn, bb(1)).getInt(), is(10));
      assertThat(dbi.get(roTxn, bb(2)).getInt(), is(20));
    }

    System.out.println("Done puts");

    final CountDownLatch firstGetFinishedLatch = new CountDownLatch(1);
    final CountDownLatch envClosedLatch = new CountDownLatch(1);

    final CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {

      System.out.println("Running async task");
      try (Txn<ByteBuffer> roTxn = env.txnRead()) {
        try (CursorIterable<ByteBuffer> iterable = dbi.iterate(roTxn, KeyRange.all())) {
          final Iterator<CursorIterable.KeyVal<ByteBuffer>> iterator = iterable.iterator();

          try {
            System.out.println("Getting first entry");
            CursorIterable.KeyVal<ByteBuffer> keyVal = iterator.next();
            assertThat(keyVal.val().getInt(), is(10));

            firstGetFinishedLatch.countDown();

            try {
              System.out.println("Waiting for env to close");
              envClosedLatch.await();
            } catch (InterruptedException e) {
              Thread.currentThread().interrupt();
              throw new RuntimeException(e);
            }

            assertThat(env.isClosed(), is(true));

            System.out.println("Getting second entry, but env is now closed");
            keyVal = iterator.next();
            assertThat(keyVal.val().getInt(), is(20));
          } catch (RuntimeException e) {
            e.printStackTrace();
          }
        }
      }
    });

    System.out.println("Waiting for cursor to get first entry");
    firstGetFinishedLatch.await();

    System.out.println("Closing env");
    env.close();
    envClosedLatch.countDown();

    System.out.println("Waiting for completion");
    future.get();
  }

Done puts
Waiting for cursor to get first entry
Running async task
Getting first entry
Waiting for env to close
Closing env
Waiting for completion
Getting second entry, but env is now closed
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00007fb5d37dab28, pid=2052, tid=2086
#
# JRE version: OpenJDK Runtime Environment (15.0.2+7) (build 15.0.2+7-27)
# Java VM: OpenJDK 64-Bit Server VM (15.0.2+7-27, mixed mode, sharing, tiered, compressed oops, g1 gc, linux-amd64)
# Problematic frame:
# C  [lmdbjava-native-library-17311548015087855682.so+0x6b28]  mdb_cursor_next+0x138
#
# No core dump will be written. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# An error report file with more information is saved as:
# /home/dev/git_work/lmdbjava/hs_err_pid2052.log
#
# If you would like to submit a bug report, please visit:
#   https://bugreport.java.com/bugreport/crash.jsp
# The crash happened outside the Java Virtual Machine in native code.
# See problematic frame for where to report the bug.
#

Process finished with exit code 134 (interrupted by signal 6: SIGABRT)