/*
 *  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.osr;

import static org.jikesrvm.runtime.UnboxedSizeConstants.LOG_BYTES_IN_ADDRESS;

import org.jikesrvm.VM;
import org.jikesrvm.mm.mminterface.Barriers;
import org.jikesrvm.runtime.Magic;
import org.vmmagic.pragma.Entrypoint;
import org.vmmagic.pragma.Inline;
import org.vmmagic.pragma.Interruptible;
import org.vmmagic.pragma.Uninterruptible;
import org.vmmagic.unboxed.Offset;

/**
 * ObjectHolder helps the specialized prologue to load reference
 * get around of GC problem.<p>
 * TODO this class needs better comments.
 */
@Uninterruptible
public class ObjectHolder {

  // initialize pool size
  private static final int POOLSIZE = 8;

  private static Object[][] refs;

  @Interruptible
  public static void boot() {
    refs = new Object[POOLSIZE][];

    // exercise the method to avoid lazy compilation in the future
    Object[] objs = new Object[1];
    int p = handinRefs(objs);
    getRefAt(p, 0);
    cleanRefs(p);

    if (VM.TraceOnStackReplacement) {
      VM.sysWriteln("ObjectHolder booted...");
    }
  }

  /*
   * TODO add better documentation and turn this into a JavaDoc comment.
   *
   * The VM scope descriptor extractor can hand in an object here
   */
  @Interruptible
  public static int handinRefs(Object[] objs) {
    int n = refs.length;
    for (int i = 0; i < n; i++) {
      if (refs[i] == null) {
        refs[i] = objs;
        return i;
      }
    }
    // grow the array
    Object[][] newRefs = new Object[2 * n][];
    System.arraycopy(refs, 0, newRefs, 0, n);
    newRefs[n] = objs;
    refs = newRefs;

    return n;
  }

  /*
   * TODO add better documentation and turn this into a JavaDoc comment.
   *
   * Get the object handed in before, only called by specialized code.
   */
  @Entrypoint
  @Inline
  public static Object getRefAt(int h, int i) {

    if (VM.TraceOnStackReplacement) {
      VM.sysWriteln("ObjectHolder getRefAt");
    }
    Object obj = refs[h][i];
    return obj;
  }

  /*
   * TODO add better documentation and turn this into a JavaDoc comment.
   *
   * Clean objects. This method is called by specialized bytecode prologue
   * Uses magic because it must be uninterruptible
   */
  @Entrypoint
  @Inline
  public static void cleanRefs(int h) {
    if (VM.TraceOnStackReplacement) {
      VM.sysWriteln("ObjectHolder cleanRefs");
    }
    /* refs[h] = null; */
    if (Barriers.NEEDS_OBJECT_ASTORE_BARRIER) {
      Barriers.objectArrayWrite(refs, h, null);
    } else {
      Magic.setObjectAtOffset(refs, Offset.fromIntSignExtend(h << LOG_BYTES_IN_ADDRESS), null);
    }
  }
}