[lqiu96]

Fixes: #12575

[gemini-code-assist]

Code Review

This pull request introduces a CountDownLatch to coordinate thread synchronization in the asynchronous single-thread test refreshCredentialsIfRequired_asyncSingleThread. The feedback points out that relying on the exact number of internal clock calls for synchronization is fragile and prone to flakiness. Instead, the reviewer recommends using a simpler CountDownLatch(1) to pause the background thread until assertions are complete, which decouples the synchronization from the clock and simplifies the mock clock implementation.

[gemini-code-assist]

Relying on the exact number of clock.currentTimeMillis() calls (numRefresh * 2 + 1) to coordinate thread synchronization is fragile. If the internal implementation of refreshCredentialsIfRequired() changes to call the clock more or fewer times, this test will become flaky or fail.

Instead, we can use a simple CountDownLatch(1) to pause the background thread in MockStsTransportFactory.create() until the main thread has finished its assertions. This completely decouples the synchronization from the internal clock calls and makes the test much more robust and maintainable.

You can then also revert the changes to createMockClock (and its signature) so it doesn't need to accept or interact with the latch.

    int numRefresh = 3;
    CountDownLatch refreshEntryLatch = new CountDownLatch(1);
    final ClientSideCredentialAccessBoundaryFactory factory =
        getClientSideCredentialAccessBoundaryFactory(RefreshType.ASYNC, refreshEntryLatch);

    // Call refreshCredentialsIfRequired() once to initialize the intermediate credentials. This
    // should make one request to the STS endpoint.
    factory.refreshCredentialsIfRequired();
    assertEquals(1, mockStsTransportFactory.transport.getRequestCount());

    try {
      // Subsequent calls to refreshCredentialsIfRequired() in an async mode should NOT
      // immediately call the STS endpoint. They should schedule an asynchronous refresh.
      for (int i = 0; i < numRefresh; i++) {
        factory.refreshCredentialsIfRequired();
      }

      // Verify that only the initial call resulted in an immediate STS request. The async refresh
      // is still pending.
      assertEquals(1, mockStsTransportFactory.transport.getRequestCount());
    } finally {
      refreshEntryLatch.countDown();
    }