// below the values of characters in surrogate pairs, this cannot occur.
    // This approach does mean that we break out of the fast path code in cases
    // where we don't strictly need to, but this situation will almost never
    // occur in practice.
    if (safeMin >= Character.MIN_HIGH_SURROGATE) {
      // The safe range is empty or the all safe code points lie in or above the

Let's start with an example and then see it in detail.

We create an async function `lifespan()` with `yield` like this:

{* ../../docs_src/events/tutorial003.py hl[16,19] *}

  /** JavaLangAccess class name to load using reflection */
  @J2ktIncompatible @GwtIncompatible // not used by GWT emulation
  private static final String JAVA_LANG_ACCESS_CLASSNAME = "sun.misc.JavaLangAccess";

  /** SharedSecrets class name to load using reflection */
  @J2ktIncompatible
  @GwtIncompatible // not used by GWT emulation
  @VisibleForTesting
  static final String SHARED_SECRETS_CLASSNAME = "sun.misc.SharedSecrets";

import java.util.Comparator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.function.Function;
import java.util.stream.Collector;
import org.jspecify.annotations.Nullable;

/**
 * GWT emulation of {@link com.google.common.collect.ImmutableBiMap}.
 *
 * @author Hayward Chan
 */
public abstract class ImmutableBiMap<K, V> extends ForwardingImmutableMap<K, V>
    implements BiMap<K, V> {

  @Override
  ContiguousSet<C> tailSetImpl(C fromElement, boolean inclusive) {
    return intersectionInCurrentDomain(Range.downTo(fromElement, BoundType.forBoolean(inclusive)));
  }

  @GwtIncompatible // not used by GWT emulation
  @Override
  int indexOf(@Nullable Object target) {
    if (!contains(target)) {
      return -1;
    }
    // The cast is safe because of the contains check—at least for any reasonable Comparable class.

It is just a standard function that can receive parameters.

It can be an `async def` or normal `def` function, **FastAPI** will know how to handle it correctly.

In this case, the task function will write to a file (simulating sending an email).

And as the write operation doesn't use `async` and `await`, we define the function with normal `def`:

{* ../../docs_src/background_tasks/tutorial001.py hl[6:9] *}

import jsinterop.annotations.JsMethod;
import jsinterop.annotations.JsPackage;
import jsinterop.annotations.JsProperty;
import jsinterop.annotations.JsType;
import org.jspecify.annotations.Nullable;

/**
 * Minimal GWT emulation of {@code com.google.common.collect.Platform}.
 *
 * @author Hayward Chan
 */
final class Platform {
  static <K extends @Nullable Object, V extends @Nullable Object>

        assertNotNull(retrieved);
        assertEquals(engine, retrieved);
    }

    // Test concurrent-like scenario (sequential but simulating concurrent behavior)
    public void test_add_multipleSameNameSequential() {
        TestScriptEngine engine1 = new TestScriptEngine("v1");
        TestScriptEngine engine2 = new TestScriptEngine("v2");

    // below the values of characters in surrogate pairs, this cannot occur.
    // This approach does mean that we break out of the fast path code in cases
    // where we don't strictly need to, but this situation will almost never
    // occur in practice.
    if (safeMin >= Character.MIN_HIGH_SURROGATE) {
      // The safe range is empty or the all safe code points lie in or above the

   * if Fire.run is called by delegate.addListener since addListener is called after the assignment
   * to timer, and importantly this is the main situation in which we need to be able to see the
   * write.
   *
   * 2. visibility of the writes to an afterDone() call triggered by cancel():
   *