///

### Path operation functions { #path-operation-functions }

When you declare a *path operation function* with normal `def` instead of `async def`, it is run in an external threadpool that is then awaited, instead of being called directly (as it would block the server).

  private ImmutableList<Integer> keys;
  private ExecutorService threadPool;

  @BeforeExperiment
  void setUp() throws Exception {
    multiset = implSupplier.get();
    ImmutableList.Builder<Integer> builder = ImmutableList.builder();
    for (int i = 0; i < size; i++) {
      builder.add(i);
    }
    keys = builder.build();
    threadPool = newFixedThreadPool(threads, new ThreadFactoryBuilder().setDaemon(true).build());

        ForkJoinPool pool1 = new ForkJoinPool(2);
        ForkJoinPool pool2 = new ForkJoinPool(4);

        // Multiple threadPool calls should work
        request.threadPool(pool1);
        request.threadPool(pool2);

        assertNotNull(request);
    }

    @Test
    public void testOnConnectWithNull() {

        connected = false;
    }

    /**
     * Gets the thread pool from the underlying client.
     *
     * @return The thread pool.
     */
    @Override
    public ThreadPool threadPool() {
        return client.threadPool();
    }

    /**
     * Gets the admin client for cluster and index operations.
     *
     * @return The admin client.
     */
    @Override

        ForkJoinPool pool = new ForkJoinPool(1);
        req.threadPool(pool);

        // ## Act ##
        // execute() should force synchronous execution but restore threadPool afterward
        try (CurlResponse response = req.execute()) {
            assertEquals(200, response.getHttpStatusCode());
        }

        // ## Assert ##
        // After execute(), the threadPool should be restored

    ExecutorService threadPool = newFixedThreadPool(nThreads);
    CountDownLatch tasksFinished = new CountDownLatch(nTasks);
    for (int i = 0; i < nTasks; i++) {
      String s = "a" + i;
      @SuppressWarnings("unused") // https://errorprone.info/bugpattern/FutureReturnValueIgnored
      Future<?> possiblyIgnoredError =
          threadPool.submit(
              () -> {

    ExecutorService threadPool = newFixedThreadPool(nThreads);
    CountDownLatch tasksFinished = new CountDownLatch(nTasks);
    for (int i = 0; i < nTasks; i++) {
      String s = "a" + i;
      @SuppressWarnings("unused") // https://errorprone.info/bugpattern/FutureReturnValueIgnored
      Future<?> possiblyIgnoredError =
          threadPool.submit(
              () -> {

        <property name="ignoreSetter" value="true" />
        <property name="setterCanReturnItsClass" value="true"/>
        <property name="ignoreFormat" value="^(threadPool)$"/>
    </module>
    -->

    <!-- We don't use Java's builtin serialization and we suppress all warning
      about it. The flip side of that coin is that we shouldn't _try_ to use

///

To avoid blocking the event loop, you can simply declare the *path operation function* with regular `def` instead of `async def`, that way FastAPI will run it on a threadpool worker, to avoid blocking the main loop.

{* ../../docs_src/stream_data/tutorial002_py310.py ln[30:34] hl[31] *}

/// tip

```Python
contents = myfile.file.read()
```

/// note | `async` Technical Details

When you use the `async` methods, **FastAPI** runs the file methods in a threadpool and awaits for them.

///

/// note | Starlette Technical Details