*
   * @throws IllegalStateException if the instance is absent ({@link #isPresent} returns {@code
   *     false}); depending on this <i>specific</i> exception type (over the more general {@link
   *     RuntimeException}) is discouraged
   */
  public abstract T get();

  /**
   * Returns the contained instance if it is present; {@code defaultValue} otherwise. If no default

 * largely defined by its supertype.
 *
 * <p>For field types and method return types, you should generally use the immutable type (such as
 * {@link ImmutableList}) instead of the general collection interface type (such as {@link List}).
 * This communicates to your callers all of the semantic guarantees listed above, which is almost
 * always very useful information.
 *

Но внутреннее устройство **конкурентности** и **параллелизма** довольно разное.

Чтобы это понять, представьте такую картину:

### Конкурентные бургеры

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</p>

<h3 id="overview">Informal Overview</h3>

<p>
Go approaches its memory model in much the same way as the rest of the language,
aiming to keep the semantics simple, understandable, and useful.
This section gives a general overview of the approach and should suffice for most programmers.
The memory model is specified more formally in the next section.
</p>

<p>
A data race is defined as

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  //    the initial write (just stronger guarantees if it does).
  //
  // See: http://cs.oswego.edu/pipermail/concurrency-interest/2015-January/013800.html
  // For a (long) discussion about this specific issue and the general futility of life.
  //
  // For the time being we are OK with the problem discussed above since it requires a caller to
  // introduce a very specific kind of data-race. And given the other operations performed by these

// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//

   * the discussion in the {@link #addListener} documentation. All its warnings about heavyweight
   * listeners are also applicable to heavyweight callbacks passed to this method.
   *
   * <p>For a more general interface to attach a completion listener, see {@link #addListener}.
   *
   * <p>This method is similar to {@link java.util.concurrent.CompletableFuture#whenComplete} and

    // 3) Create RepositorySystemSession.
    //
    // 4) Create MavenSession.
    //
    // 5) Execute AbstractLifecycleParticipant.afterSessionStart(session)
    //
    // 6) Get reactor projects looking for general POM errors
    //
    // 7) Create ProjectDependencyGraph using trimming which takes into account --projects and reactor mode.
    // This ensures that the projects passed into the ReactorReader are only those specified.

   * is. The {@code equals} and {@code hashCode} methods of the returned multimap are meaningless,
   * since there is not a definition of {@code equals} or {@code hashCode} for general collections,
   * and {@code get()} will return a general {@code Collection} as opposed to a {@code List} or a
   * {@code Set}.
   *
   * <p>The function is applied lazily, invoked when needed. This is necessary for the returned