* detect if followups need to do a full connection-finding process including DNS resolution, and
   * certificate pin checks.
   */
  fun sameHostAndPort(url: HttpUrl): Boolean

  /**
   * A plan holds either an immediately-usable connection, or one that must be connected first.
   * These steps are split so callers can call [connectTcp] on a background thread if attempting
   * multiple plans concurrently.
   */
  interface Plan {

   *
   * <p>The returned executor is backed by the executor returned by {@link
   * MoreExecutors#newDirectExecutorService} and subject to the same constraints.
   *
   * <p>Although all tasks are immediately executed in the thread that submitted the task, this
   * {@code ExecutorService} imposes a small locking overhead on each task submission in order to
   * implement shutdown and termination behavior.
   *

      // and when it is done will run the listeners.
      if (hasListeners.compareAndSet(false, true)) {
        if (delegate.isDone()) {
          // If the delegate is already done, run the execution list immediately on the current
          // thread.
          executionList.execute();
          return;
        }

        // TODO(lukes): handle RejectedExecutionException
        adapterExecutor.execute(

   *
   * <p>The returned executor is backed by the executor returned by {@link
   * MoreExecutors#newDirectExecutorService} and subject to the same constraints.
   *
   * <p>Although all tasks are immediately executed in the thread that submitted the task, this
   * {@code ExecutorService} imposes a small locking overhead on each task submission in order to
   * implement shutdown and termination behavior.
   *

are working on. And as mentioned above, API changes should be discussed
thoroughly before moving to code.

Some examples of types of pull requests that are immediately helpful:

  - Fixing a bug without changing a public API.
  - Fixing or improving documentation.
  - Improvements to Maven configuration.

Guidelines for any code contributions:

import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * A ScheduledExecutorService that executes all scheduled actions immediately in the calling thread.
 *
 * <p>See {@link TestingExecutors#sameThreadScheduledExecutor()} for a full list of constraints.
 *
 * @author John Sirois
 * @author Zach van Schouwen
 */
@GwtIncompatible

import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * A ScheduledExecutorService that executes all scheduled actions immediately in the calling thread.
 *
 * <p>See {@link TestingExecutors#sameThreadScheduledExecutor()} for a full list of constraints.
 *
 * @author John Sirois
 * @author Zach van Schouwen
 */
@GwtIncompatible

    RateLimiter limiter = RateLimiter.create(5.0, stopwatch);
    limiter.acquire(); // R0.00
    stopwatch.sleepMillis(200); // U0.20, we are ready for the next request...
    limiter.acquire(); // R0.00, ...which is granted immediately
    limiter.acquire(); // R0.20
    assertEvents("R0.00", "U0.20", "R0.00", "R0.20");
  }

  public void testSimpleAcquireReturnValues() {
    RateLimiter limiter = RateLimiter.create(5.0, stopwatch);

    RateLimiter limiter = RateLimiter.create(5.0, stopwatch);
    limiter.acquire(); // R0.00
    stopwatch.sleepMillis(200); // U0.20, we are ready for the next request...
    limiter.acquire(); // R0.00, ...which is granted immediately
    limiter.acquire(); // R0.20
    assertEvents("R0.00", "U0.20", "R0.00", "R0.20");
  }

  public void testSimpleAcquireReturnValues() {
    RateLimiter limiter = RateLimiter.create(5.0, stopwatch);

     * simple approach would be for each caller CAS it from null to a Set populated with its
     * exception. But there's another race: If the first thread fails with an exception and a second
     * thread immediately fails with the same exception:
     *
     * Thread1: calls setException(), which returns true, context switch before it can CAS
     * seenExceptionsField to its exception
     *