# 펜스 메서드가 돌려주는 값과 그 javadoc
  /**
   * Unfenced: the engine's lock exposes no monotonic token.
   *
   * <p>Reported honestly rather than synthesised from a local counter, which would look like
   * fencing and protect nothing — a per-process counter says nothing about what another process
   * acquired. The runner refuses resumable migrations under an unfenced lease for exactly this
   * reason.
   */
  @Override
  public long fence() {
    return UNFENCED;
  }

# 실행자의 진입점이 지나는 세 관문
    Objects.requireNonNull(context, "context");
    if (!lock.held()) {
      throw MongoOperationRejectedException.of(
          "migration.lock",
          "the migration lease is not held; only one runner may apply changes at a time");
    }

    migrations.forEach(this::validate);

    if (lock.fence() == MongoMigrationLock.UNFENCED) {
      // An unfenced lease cannot tell a live runner from a stalled one that is about to wake up.
      // Refused rather than downgraded: the alternative is a certification that says "one runner at
      // a time" and a mechanism that cannot show it.
      throw MongoOperationRejectedException.of(
          "migration.fence",
          "this migration lease exposes no fencing token, so a stalled runner cannot be excluded;"
              + " use a fenced lease or run the migration inside a maintenance window with the"
              + " application stopped");
    }

    return migrations.stream()

#   그 파일에서 리스의 펜스를 읽는 곳 전수
80:    migrations.forEach(this::validate);
82:    if (lock.fence() == MongoMigrationLock.UNFENCED) {
93:    return migrations.stream()
154:    result.resumePoint().ifPresent(checkpoint -> ledger.saveCheckpoint(checkpoint, lock.fence()));
157:          migration.id(), migration.checksum(), context.operator(), clock.instant(), lock.fence());

#   154행이 넘기는 곳과 157행이 넘기는 곳이 그 값을 다루는 방식
93:    requireCurrentFence(fence, "ledger entry for " + migrationId.value());
120:    requireCurrentFence(fence, "checkpoint for " + checkpoint.migrationId().value());
177:  private static void requireCurrentFence(long fence, String what) {
    if (fence == MongoMigrationLock.UNFENCED) {
      throw MongoOperationRejectedException.of(
          "migration.fence",
          "refusing to write the "

#   마이그레이션이 재개 가능한지 실행 전에 알 수 있는가
17:  MongoMigrationId id();
20:  MongoMigrationChecksum checksum();
23:  MongoMigrationPrecondition precondition();
26:  MongoMigrationResult execute(MongoMigrationContext context);
29:  MongoMigrationPostcondition postcondition();

# 이 잠금 어댑터가 나오는 곳 전수
test/java/dev/caskeleton/adapter/outbound/mongo/migration/flamingock/FlamingockMongoMigrationAdapterTest.java:58:    assertThatThrownBy(() -> new FlamingockLockAdapter(() -> false, extension -> {}, () -> {}))
test/java/dev/caskeleton/adapter/outbound/mongo/migration/flamingock/FlamingockMongoMigrationAdapterTest.java:65:    FlamingockLockAdapter lock =
test/java/dev/caskeleton/adapter/outbound/mongo/migration/flamingock/FlamingockMongoMigrationAdapterTest.java:66:        new FlamingockLockAdapter(() -> true, extension -> {}, () -> released.set(true));
main/java/dev/caskeleton/adapter/outbound/mongo/migration/flamingock/FlamingockLockAdapter.java:17:public final class FlamingockLockAdapter implements MongoMigrationLock {
main/java/dev/caskeleton/adapter/outbound/mongo/migration/flamingock/FlamingockLockAdapter.java:25:  public FlamingockLockAdapter(

# 실행자와 원장과 잠금을 프로덕션에서 참조하는 곳
  (없음)

# 마이그레이션을 적용하는 진입점 전수
test/java/dev/caskeleton/adapter/outbound/mongo/migration/MongoMigrationLaneTest.java:81:        List<MongoMigrationResult> results =
main/java/dev/caskeleton/adapter/outbound/mongo/migration/MongoMigrationRunner.java:69:  public List<MongoMigrationResult> apply(