// For GCM, last 4 bytes should contain incrementing counter
        ByteBuffer buffer1 = ByteBuffer.wrap(nonce1, 12, 4).order(java.nio.ByteOrder.LITTLE_ENDIAN);
        ByteBuffer buffer2 = ByteBuffer.wrap(nonce2, 12, 4).order(java.nio.ByteOrder.LITTLE_ENDIAN);
        int counter1 = buffer1.getInt();
        int counter2 = buffer2.getInt();

        assertEquals(counter1 + 1, counter2, "Counter should increment between nonces");
    }

        AtomicInteger counter1 = new AtomicInteger(0);
        AtomicInteger counter2 = new AtomicInteger(0);

        executor1.addShutdownListener(() -> counter1.incrementAndGet());
        executor2.addShutdownListener(() -> counter2.incrementAndGet());

        executor1.shutdown();
        assertEquals(1, counter1.get());
        assertEquals(0, counter2.get());

        executor2.shutdown();

    public void test_concurrent_stores() {
        // Test thread-safe implementation
        final AtomicLong counter = new AtomicLong(0);

        IndexUpdateCallback callback = new IndexUpdateCallback() {
            @Override
            public void store(DataStoreParams paramMap, Map<String, Object> dataMap) {
                counter.incrementAndGet();
            }

            @Override
            public long getDocumentSize() {

        long currentWindow = System.currentTimeMillis() / rateLimitWindow;
        String windowKey = key + "_" + currentWindow;

        AtomicLong counter = rateLimitCounters.computeIfAbsent(windowKey, k -> new AtomicLong(0));
        long currentCount = counter.incrementAndGet();

        // Clean up old windows periodically
        if (currentCount == 1) {
            cleanupOldRateLimitCounters(currentWindow);
        }

This is different from using an `APIRouter` as a mounted application is completely independent. The OpenAPI and docs from your main application won't include anything from the mounted application, etc.

You can read more about this in the [Advanced User Guide](../advanced/index.md){.internal-link target=_blank}.

## Details { #details }

This sub-application is just another standard FastAPI application, but this is the one that will be "mounted":

{* ../../docs_src/sub_applications/tutorial001.py hl[11, 14:16] *}

### Mount the sub-application { #mount-the-sub-application }

In your top-level application, `app`, mount the sub-application, `subapi`.

In this case, it will be mounted at the path `/subapi`:

{* ../../docs_src/sub_applications/tutorial001.py hl[11, 19] *}

            buffer.putInt((int) counter);
        } else {
            // SMB 3.0/3.0.2 CCM: Counter-based approach as per SMB3 specification
            final long counter = this.nonceCounter.incrementAndGet();
            final ByteBuffer buffer = ByteBuffer.wrap(nonce);
            buffer.order(java.nio.ByteOrder.LITTLE_ENDIAN);
            buffer.putLong(counter);
            // Remaining bytes (if any) stay zero-padded

    private void setupMockComponentsWithCounter(final AtomicInteger counter) {
        setupMockComponents();

        // Override thumbnail manager with counter
        ThumbnailManager mockThumbnailManager = new ThumbnailManager() {
            @Override
            public int generate(ExecutorService executorService, boolean cleanup) {
                counter.incrementAndGet();
                // Return 0 to exit the loop

While waiting and talking to your crush, from time to time, you check the number displayed on the counter to see if it's your turn already.

Then at some point, it finally is your turn. You go to the counter, get your burgers and come back to the table.

<img src="/img/async/concurrent-burgers/concurrent-burgers-06.png" class="illustration">

            // If we need more bytes, hash again with counter
            int counter = 1;
            while (derived.length > hash.length * counter) {
                md.update(input);
                md.update((byte) counter);
                hash = md.digest();
                int copyLen = Math.min(length - (hash.length * counter), hash.length);