* operations in the search engine. It supports recursive crawling with configurable depth and access count limits.
 *
 * <p>The implementation uses an executor service for concurrent processing of file operations and maintains
 * a cache of URLs to be deleted for batch processing. It handles redirect following and child URL discovery
 * during the crawling process.</p>
 */
public class FileListIndexUpdateCallbackImpl implements IndexUpdateCallback {

    try {
      return type.cast(arg);
    } catch (ClassCastException e) {
      throw new IllegalArgumentException(arg + " is not a " + type.getSimpleName());
    }
  }

  /** A TypeTable maintains mapping from {@link TypeVariable} to types. */
  private static class TypeTable {
    private final ImmutableMap<TypeVariableKey, Type> map;

    TypeTable() {
      this.map = ImmutableMap.of();
    }

   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
   * set a value to {@code null} will result in a {@link NullPointerException}.
   *
   * <p>The returned list maintains the values, but not the identities, of {@code Integer} objects
   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *

are predefined and refer to registers.
The exact set depends on the architecture.
</p>

<p>
There are four predeclared symbols that refer to pseudo-registers.
These are not real registers, but rather virtual registers maintained by
the toolchain, such as a frame pointer.
The set of pseudo-registers is the same for all architectures:
</p>

<ul>

<li>
<code>FP</code>: Frame pointer: arguments and locals.
</li>

<li>

   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
   * set a value to {@code null} will result in a {@link NullPointerException}.
   *
   * <p>The returned list maintains the values, but not the identities, of {@code Character} objects
   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *

   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
   * set a value to {@code null} will result in a {@link NullPointerException}.
   *
   * <p>The returned list maintains the values, but not the identities, of {@code Float} objects
   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *

   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
   * set a value to {@code null} will result in a {@link NullPointerException}.
   *
   * <p>The returned list maintains the values, but not the identities, of {@code Double} objects
   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *

import java.util.Comparator;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.jspecify.annotations.Nullable;

/**
 * A multiset which maintains the ordering of its elements, according to either their natural order
 * or an explicit {@link Comparator}. In all cases, this implementation uses {@link

 * passive/active modes, and encoding settings. It also handles FTP file attributes such as user,
 * group, and symbolic links.
 *
 * <p>
 * The class uses Apache Commons Net library for FTP communication. It maintains a queue of FTPClient
 * instances to improve performance by reusing connections.
 * </p>
 *
 * <p>
 * The client can be configured with FTP-specific settings via init parameters, such as:
 * </p>
 * <ul>

   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
   * set a value to {@code null} will result in a {@link NullPointerException}.
   *
   * <p>The returned list maintains the values, but not the identities, of {@code Long} objects
   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *