/*
 *  This file is part of the Jikes RVM project (http://jikesrvm.org).
 *
 *  This file is licensed to You under the Eclipse Public License (EPL);
 *  You may not use this file except in compliance with the License. You
 *  may obtain a copy of the License at
 *
 *      http://www.opensource.org/licenses/eclipse-1.0.php
 *
 *  See the COPYRIGHT.txt file distributed with this work for information
 *  regarding copyright ownership.
 */
package org.jikesrvm.objectmodel;

import org.jikesrvm.VM;
import org.jikesrvm.compilers.common.CodeArray;
import org.vmmagic.Intrinsic;
import org.vmmagic.pragma.NonMoving;
import org.vmmagic.pragma.Uninterruptible;
import org.vmmagic.pragma.UninterruptibleNoWarn;

/**
 * This class represents an instance of an interface method table, at runtime it
 * is an array with CodeArray elements.
 */
@NonMoving
public final class IMT implements RuntimeTable<CodeArray> {

  /**
   * The backing data used during boot image writing.
   */
  private final CodeArray[] data;

  /**
   * Private constructor. Can not create instances.
   */
  private IMT() {
    this.data = new CodeArray[TIBLayoutConstants.IMT_METHOD_SLOTS];
  }

  @Override
  public CodeArray[] getBacking() {
    if (VM.VerifyAssertions) VM._assert(!VM.runningVM);
    return data;
  }

  /**
   * Creates an IMT.
   *
   * @return The created IMT instance.
   */
  public static IMT allocate() {
    if (VM.VerifyAssertions && VM.runningVM) VM._assert(VM.NOT_REACHED);
    return new IMT();
  }

  /**
   * Gets an entry in the IMT.
   *
   * @param index The index of the entry to get
   * @return The value of that entry
   */
  @Override
  @Intrinsic
  @Uninterruptible
  public CodeArray get(int index) {
    if (VM.VerifyAssertions && VM.runningVM) VM._assert(VM.NOT_REACHED);
    return data[index];
  }

  /**
   * Sets an entry in the IMT.
   *
   * @param index The index of the entry to set
   * @param value The value to set the entry to.
   */
  @Override
  @Intrinsic
  @UninterruptibleNoWarn("Interruptible code not reachable at runtime")
  public void set(int index, CodeArray value) {
    if (VM.VerifyAssertions && VM.runningVM) VM._assert(VM.NOT_REACHED);
    data[index] = value;
  }

  /**
   * Returns the length of the IMT
   */
  @Override
  @Intrinsic
  @Uninterruptible
  public int length() {
    if (VM.VerifyAssertions && VM.runningVM) VM._assert(VM.NOT_REACHED);
    return data.length;
  }
}