// Test thread safety of fillInStackTrace method
        UserRoleLoginException exception = new UserRoleLoginException(RootAction.class);

        // Create multiple threads to test synchronized method
        Thread thread1 = new Thread(() -> {
            Throwable result = exception.fillInStackTrace();
            assertNull(result);
        });

        Thread thread2 = new Thread(() -> {

    TearDownStack result = new TearDownStack();
    tearDownStack.addTearDown(
        new TearDown() {

          @Override
          public void tearDown() throws Exception {
            synchronized (result.lock) {
              assertEquals(
                  "The test should have cleared the stack (say, by virtue of running runTearDown)",
                  0,
                  result.stack.size());

                        BufferCache.releaseBuffer(buffer);
                        successCount.incrementAndGet();
                    }
                } catch (Exception e) {
                    synchronized (exceptions) {
                        exceptions.add(e);
                    }
                } finally {
                    endLatch.countDown();
                }
            });
        }

  }

  private static class TestApplication extends Application {
    private final List<Thread> hooks = new ArrayList<>();

    @Override
    synchronized void addShutdownHook(Thread hook) {
      hooks.add(hook);
    }

    synchronized void shutdown() throws InterruptedException {
      for (Thread hook : hooks) {
        hook.start();
      }
      for (Thread hook : hooks) {
        hook.join();

                            boolean contains = pool.contains(null); // Should handle gracefully
                            successCount.incrementAndGet();
                        } catch (Exception e) {
                            synchronized (exceptions) {
                                exceptions.add(e);
                            }
                        }
                    }
                    long threadEnd = System.nanoTime();

    assertTrue(Thread.holdsLock(mutex));
    return super.isEmpty();
  }

  /*
   * We don't assert that the lock is held during calls to iterator(), stream(), and spliterator:
   * `Synchronized` doesn't guarantee that it will hold the mutex for those calls because callers
   * are responsible for taking the mutex themselves:

        }
        buffer.setLength(buffer.length() - ", ".length());
        return new String(buffer);
    }

    /**
     * Initializes the class.
     */
    protected static synchronized void initialize() {
        if (!initialized) {
            DisposableUtil.add(() -> {
                ResourceBundle.clearCache();
                initialized = false;
            });

    private static class IOExceptionOccurProperties extends Properties {

        /**
         *
         */
        private static final long serialVersionUID = 1L;

        @Override
        public synchronized void load(final InputStream inStream) throws IOException {
            throw new IOException("load");
        }

    }

    /**
     * {@link org.codelibs.core.io.PropertiesUtil#load(Properties, String)}

        // When - Release session to trigger cleanup
        session.release();

        // Then - Trees should be cleared (we can't directly verify as it's internal,
        // but the cleanup code with synchronized block ensures it happens atomically)
        // The important part is that no exception occurs and the operation is atomic
    }

    /**
     * Test concurrent acquire and release operations.
     */

    address: Address,
    connectionUser: ConnectionUser,
    routes: List<Route>?,
    requireMultiplexed: Boolean,
  ): RealConnection? {
    for (connection in connections) {
      // In the first synchronized block, acquire the connection if it can satisfy this call.
      val acquired =
        connection.withLock {
          when {
            requireMultiplexed && !connection.isMultiplexed -> false