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] *}

```html
<a href="/items/42">
```

## Templates and static files { #templates-and-static-files }

You can also use `url_for()` inside of the template, and use it, for example, with the `StaticFiles` you mounted with the `name="static"`.

```jinja hl_lines="4"
{!../../docs_src/templates/templates/item.html!}
```

In this example, it would link to a CSS file at `static/styles.css` with:

```CSS hl_lines="4"

**Note**: this is a very technical detail that you probably can **just skip**.

---

The `APIRouter`s are not "mounted", they are not isolated from the rest of the application.

This is because we want to include their *path operations* in the OpenAPI schema and the user interfaces.

As we cannot just isolate them and "mount" them independently of the rest, the *path operations* are "cloned" (re-created), not included directly.

///

- Stopped removing the CSI JSON file if the volume was already mounted during subsequent errors. ([#131311](https://github.com/kubernetes/kubernetes/pull/131311), [@gnufied](https://github.com/gnufied))

    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);
        }

        }

        // Then - Check that counter portion has entropy
        // For SMB3-compliant nonces, the first 8 bytes are a counter (little-endian)
        // so we check that the counter bytes change as expected
        Set<String> uniqueCounters = new HashSet<>();
        for (int i = 0; i < sampleSize; i++) {
            // Extract first 8 bytes as counter
            byte[] counter = new byte[8];

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">

    }

    @Test
    @DisplayName("Test run method")
    void testRunMethod() throws Exception {
        AtomicInteger counter = new AtomicInteger(0);

        circuitBreaker.run(() -> counter.incrementAndGet());
        assertEquals(1, counter.get());

        SimpleCircuitBreaker.Statistics stats = circuitBreaker.getStatistics();
        assertEquals(1, stats.totalCalls);