// Fail fast if there's no response queued up.
      return failFastResponse!!
    }

    val result = responseQueue.take()

    // If take() returned because we're shutting down, then enqueue another dead letter so that any
    // other threads waiting on take() will also return.
    if (result == DEAD_LETTER) responseQueue.add(DEAD_LETTER)

    return result
  }

### Create a dependency, or "dependable" { #create-a-dependency-or-dependable }

Let's first focus on the dependency.

It is just a function that can take all the same parameters that a *path operation function* can take:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

That's it.

**2 lines**.

And it has the same shape and structure that all your *path operation functions* have.

     */
    Source getGlobalToolchainsSource();

    /**
     * Sets the global toolchains source. If both user toolchains and a global toolchains are given, the user toolchains
     * take precedence.
     *
     * @param globalToolchainsSource The global toolchains source, may be {@code null} to disable global toolchains.
     * @return This request, never {@code null}.
     */

    // Explicit replacements take priority over unsafe characters.
    builder.addEscape(' ', "_");
    builder.addEscape('!', "_");
    assertThat(builder.build().escape("The Quick Brown Fox!")).isEqualTo("Xhe_Xuick_Xrown_Xox_");
    // Explicit replacements take priority over safe characters.
    builder.setSafeRange(' ', '~');

For this, use the Python standard module <a href="https://docs.python.org/3/library/secrets.html" class="external-link" target="_blank">`secrets`</a> to check the username and password.

`secrets.compare_digest()` needs to take `bytes` or a `str` that only contains ASCII characters (the ones in English), this means it wouldn't work with characters like `á`, as in `Sebastián`.

### FastAPI Data Filtering { #fastapi-data-filtering }

Now, for FastAPI, it will see the return type and make sure that what you return includes **only** the fields that are declared in the type.

Instead of that, by being an "asynchronous" system, once finished, the task can wait in line a little bit (some microseconds) for the computer / program to finish whatever it went to do, and then come back to take the results and continue working with them.

   *
   * @param eventClass a class to assert that the returned event is an instance of, or null to
   *     take any event class.
   * @param elapsedMs the time in milliseconds elapsed since the immediately-preceding event, or
   *     -1L to take any duration.
   */
  fun takeEvent(
    eventClass: Class<out CallEvent>? = null,
    elapsedMs: Long = -1L,
  ): CallEvent {

      // we allow one second worth of work to go in a burst (i.e. take less than a second)
      assertThat(burst).isAtMost(1000);
      long afterBurst = measureTotalTimeMillis(limiter, oneSecWorthOfWork, new Random());
      // but work beyond that must take at least one second
      assertThat(afterBurst).isAtLeast(1000);
    }
  }

  /**

      // we allow one second worth of work to go in a burst (i.e. take less than a second)
      assertThat(burst).isAtMost(1000);
      long afterBurst = measureTotalTimeMillis(limiter, oneSecWorthOfWork, new Random());
      // but work beyond that must take at least one second
      assertThat(afterBurst).isAtLeast(1000);
    }
  }

  /**