blocker.setOwner(Thread.currentThread());
      if (compareAndSet(currentRunner, blocker)) {
        // Thread.interrupt can throw arbitrary exceptions due to the nio InterruptibleChannel API
        // This will make sure that tasks don't get stuck busy waiting.
        // Some of this is fixed in jdk11 (see https://bugs.openjdk.org/browse/JDK-8198692) but
        // not all.  See the test cases for examples on how this can happen.
        try {

  }

  /** If we don't keep a strong reference to the reference object, it won't be enqueued. */
  @Nullable FinalizableWeakReference<Object> reference;

  /** Create the FRQ in a method that goes out of scope so that we're sure it will be reclaimed. */
  private void weaklyReferenceQueue() {
    frq = new FinalizableReferenceQueue();
    queueReference = new WeakReference<>(frq.queue);

    /*

  }

  /** If we don't keep a strong reference to the reference object, it won't be enqueued. */
  @Nullable FinalizableWeakReference<Object> reference;

  /** Create the FRQ in a method that goes out of scope so that we're sure it will be reclaimed. */
  private void weaklyReferenceQueue() {
    frq = new FinalizableReferenceQueue();
    queueReference = new WeakReference<>(frq.queue);

    /*

You can use <a href="https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API" class="external-link" target="_blank">WebSockets</a> with **FastAPI**.

## Install `WebSockets` { #install-websockets }

Make sure you create a [virtual environment](../virtual-environments.md){.internal-link target=_blank}, activate it, and install `websockets`:

<div class="termy">

```console
$ pip install websockets

---> 100%
```

/// tip

Review what each line does by clicking each number bubble in the code. 👆

///

/// warning

Make sure to **always** use the **exec form** of the `CMD` instruction, as explained below.

///

#### Use `CMD` - Exec Form { #use-cmd-exec-form }

   */
  private fun planReuseCallConnection(): ReusePlan? {
    // This may be mutated by releaseConnectionNoEvents()!
    val candidate = connectionUser.candidateConnection() ?: return null

    // Make sure this connection is healthy & eligible for new exchanges. If it's no longer needed
    // then we're on the hook to close it.
    val healthy = candidate.isHealthy(connectionUser.doExtensiveHealthChecks())

```

Snapshot builds are [available][snap]. [R8 and ProGuard][r8_proguard] rules are available.

Also, we have a [bill of materials (BOM)][bom] available to help you keep OkHttp artifacts up to date and be sure about version compatibility.

```kotlin
    dependencies {
       // define a BOM and its version
       implementation(platform("com.squareup.okhttp3:okhttp-bom:5.1.0"))

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

But possibly the most important part of the callback is making sure that your API user (the external developer) implements the *external API* correctly, according to the data that *your API* is going to send in the request body of the callback, etc.

		return 1, err
	}

	// This wrapper uses complicated machinery to run iOS binaries. It
	// works, but only when running one binary at a time.
	// Use a file lock to make sure only one wrapper is running at a time.
	//
	// The lock file is never deleted, to avoid concurrent locks on distinct
	// files with the same path.
	lockName := filepath.Join(os.TempDir(), "go_ios_exec-"+deviceID+".lock")

/// info

FastAPI added support for `Annotated` (and started recommending it) in version 0.95.0.

If you have an older version, you would get errors when trying to use `Annotated`.

Make sure you [Upgrade the FastAPI version](../../deployment/versions.md#upgrading-the-fastapi-versions){.internal-link target=_blank} to at least 0.95.1 before using `Annotated`.

///

### Import `Depends` { #import-depends }