* hashmaps. Using a static ThreadLocal to avoid that overhead would mean that different
   * ExecutionSequencer objects interfere with each other, which would be undesirable, in addition
   * to increasing the memory footprint of every thread that interacted with it. In order to release
   * entries in thread-specific maps when the ThreadLocal object itself is no longer referenced,

  /**
   * The current state of the service. This should be written with the lock held but can be read
   * without it because it is an immutable object in a volatile field. This is desirable so that
   * methods like {@link #state}, {@link #failureCause} and notably {@link #toString} can be run
   * without grabbing the lock.
   *

  Simply including a copy of this Agreement, including this Exhibit A
  is not sufficient to license the Source Code under Secondary Licenses.

  If it is not possible or desirable to put the notice in a particular
  file, then You may include the notice in a location (such as a LICENSE
  file in a relevant directory) where a recipient would be likely to
  look for such a notice.

  /**
   * The current state of the service. This should be written with the lock held but can be read
   * without it because it is an immutable object in a volatile field. This is desirable so that
   * methods like {@link #state}, {@link #failureCause} and notably {@link #toString} can be run
   * without grabbing the lock.
   *