# Reference

Here's the reference or code API, the classes, functions, parameters, attributes, and
all the FastAPI parts you can use in your applications.

If you want to **learn FastAPI** you are much better off reading the

### Is concurrency better than parallelism? { #is-concurrency-better-than-parallelism }

Nope! That's not the moral of the story.

Concurrency is different than parallelism. And it is better on **specific** scenarios that involve a lot of waiting. Because of that, it generally is a lot better than parallelism for web application development. But not for everything.

			} else {
				break
			}
			n++
		}

		// Prompt for decryption key if no --key or --private-key are provided
		if len(privateKeys) == 0 && !*stdin {
			reader := bufio.NewReader(os.Stdin)
			fmt.Print("Enter Decryption Key: ")

			text, _ := reader.ReadString('\n')
			// convert CRLF to LF
			*keyHex = strings.ReplaceAll(text, "\n", "")
			*keyHex = strings.TrimSpace(*keyHex)
		}
	}

	var inputs []string

      render: shell
    validations:
      required: true
  - type: textarea
    id: what-did-you-do
    attributes:
      label: "What did you do?"
      description: "If possible, provide a recipe for reproducing the error. A complete runnable program is good. A link on [go.dev/play](https://go.dev/play) is better. A failing unit test is the best."
    validations:

    // unless it's actually going to be used; validate() is called for all set method calls, so it
    // needs to be fast.
    // (We could instead generate the message once, when the set is created, but zero is better.)
    if (!validator.get()) {
      throw new IllegalStateException(errorMessage.get());
    }
  }

I (the author, [@tiangolo](https://x.com/tiangolo)) will review it thoroughly and get back to you.

## Public Discussions

Please restrain from publicly discussing a potential security vulnerability. 🙊

It's better to discuss privately and try to find a solution first, to limit the potential impact as much as possible.

---

Thanks for your help!

{* ../../docs_src/path_params_numeric_validations/tutorial003.py hl[7] *}

### Better with `Annotated` { #better-with-annotated }

Keep in mind that if you use `Annotated`, as you are not using function parameter default values, you won't have this problem, and you probably won't need to use `*`.

 * of EventBus may be better written using <a
 * href="https://kotlinlang.org/docs/coroutines-guide.html">Kotlin coroutines</a>, including <a
 * href="https://kotlinlang.org/docs/flow.html">Flow</a> and <a
 * href="https://kotlinlang.org/docs/channels.html">Channels</a>. Yet other usages are better served
 * by individual libraries that provide specialized support for particular use cases.
 *

    linkedHashMultiset = LinkedHashMultiset.create(size);
    treeMultiset = TreeMultiset.create();

    Random random = new Random();

    int sizeRemaining = size;

    // TODO(kevinb): generate better test contents for multisets
    while (sizeRemaining > 0) {
      // The JVM will return interned values for small ints.
      Integer value = random.nextInt(1000) + 128;

If you want to secure your API, there are several better things you can do, for example:

* Make sure you have well defined Pydantic models for your request bodies and responses.
* Configure any required permissions and roles using dependencies.