For "synchronous" (contrary to "asynchronous") they commonly also use the term "sequential", because the computer / program follows all the steps in sequence before switching to a different task, even if those steps involve waiting.

### Concurrency and Burgers { #concurrency-and-burgers }

import java.util.concurrent.Executors
import java.util.concurrent.TimeUnit
import java.util.logging.Logger
import okhttp3.TestUtil.threadFactory

/**
 * Runs a [TaskRunner] in a controlled environment so that everything is sequential and
 * deterministic.
 *
 * This class ensures that at most one thread is running at a time. This is initially the JUnit test
 * thread, which yields its execution privilege while calling [runTasks], [runNextTask], or

		default:
			return nil, ErrUnsignedHeaders
		}
	}
	return extractedSignedHeaders, ErrNone
}

// Trim leading and trailing spaces and replace sequential spaces with one space, following Trimall()
// in http://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html
func signV4TrimAll(input string) string {
	// Compress adjacent spaces (a space is determined by

                    }
                    return transform(fromList, removeFirst);
                  }
                })
            .named("Lists.transform, sequential access, no nulls")
            .withFeatures(
                CollectionSize.ANY,
                ListFeature.REMOVE_OPERATIONS,
                CollectionFeature.SERIALIZABLE,

 * methods, like stream(Iterable), we have to rely on users not to call them without library
 * desugaring.
 */
@IgnoreJRERequirement
public final class Streams {
  /**
   * Returns a sequential {@link Stream} of the contents of {@code iterable}, delegating to {@link
   * Collection#stream} if possible.
   */
  public static <T extends @Nullable Object> Stream<T> stream(Iterable<T> iterable) {

then <i>A</i> is synchronized before <i>B</i>.
All the atomic operations executed in a program behave as though executed
in some sequentially consistent order.
</p>

<p>
The preceding definition has the same semantics as C++’s sequentially consistent atomics
and Java’s <code>volatile</code> variables.
</p>

<h3 id="finalizer">Finalizers</h3>

<p>

/**
 * Static utility methods related to {@code Stream} instances.
 *
 * @since 21.0 (but only since 33.4.0 in the Android flavor)
 */
@GwtCompatible
public final class Streams {
  /**
   * Returns a sequential {@link Stream} of the contents of {@code iterable}, delegating to {@link
   * Collection#stream} if possible.
   */
  public static <T extends @Nullable Object> Stream<T> stream(Iterable<T> iterable) {

// large to fit in the [Scanner.Buffer]. When a scan stops, the reader may have
// advanced arbitrarily far past the last token. Programs that need more
// control over error handling or large tokens, or must run sequential scans
// on a reader, should use [bufio.Reader] instead.
type Scanner struct {
	r            io.Reader // The reader provided by the client.
	split        SplitFunc // The function to split the tokens.

      "FINE: Q10000 starting              : task",
      "FINE: Q10000 finished run in   0 µs: task",
    )
  }

  /** Inspect how many runnables have been enqueued. If none then we're truly sequential. */
  @Test fun singleQueueIsSerial() {
    redQueue.execute("task one", 100.µs) {
      log += "one:run@${taskFaker.nanoTime} parallel=${taskFaker.isParallel}"
    }

    redQueue.execute("task two", 100.µs) {

之所以稱為「非同步」，是因為電腦/程式不需要與那些耗時的任務「同步」，等待任務完成的精確時間，然後才能取得結果並繼續工作。

相反地，非同步系統在任務完成後，可以讓任務稍微等一下（幾微秒），等待電腦/程式完成手頭上的其他工作，然後再回來取得結果繼續進行。

相對於「非同步」（asynchronous），「同步」（synchronous）也常被稱作「順序性」（sequential），因為電腦/程式會依序執行所有步驟，即便這些步驟涉及等待，才會切換到其他任務。

### 並行與漢堡

上述非同步程式碼的概念有時也被稱為「並行」，它不同於「平行」。

並行和平行都與 "不同的事情或多或少同時發生" 有關。

但並行和平行之間的細節是完全不同的。

為了理解差異，請想像以下有關漢堡的故事：

### 並行漢堡