//===--------------- Barriers.java - Barriers for J3 ----------------------===//
//
//                            The VMKit project
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

package org.j3.mmtk;

import org.jikesrvm.Magic;
import org.vmmagic.unboxed.*;
import org.vmmagic.pragma.*;

public final class Barriers extends org.mmtk.vm.Barriers {
  /**
   * Perform the actual write of the write barrier.
   *
   * @param ref The object that has the reference field
   * @param slot The slot that holds the reference
   * @param target The value that the slot will be updated to
   * @param metaDataA The offset from the ref
   * @param metaDataB The index of the FieldReference
   * @param mode The context in which the write is occuring
   */
  @Inline
  public final void performWriteInBarrier(ObjectReference ref, Address slot,
                                           ObjectReference target, Word metaDataA,
                                           Word metaDataB, int mode) {
    Object obj = ref.toObject();
    Offset offset = metaDataA.toOffset();
    int location = metaDataB.toInt();
    Magic.setObjectAtOffset(obj, offset, target.toObject(), location);
  }

  /**
   * Perform the actual write of the write barrier, writing the value as a raw word.
   *
   * @param ref The object that has the reference field
   * @param slot The slot that holds the reference
   * @param rawTarget The value that the slot will be updated to
   * @param metaDataA The offset from the ref
   * @param metaDataB The index of the FieldReference
   * @param mode The context in which the write is occuring
   */
  @Inline
  public final void performRawWriteInBarrier(ObjectReference ref, Address slot,
                                             Word rawTarget, Word metaDataA,
                                             Word metaDataB, int mode) {
    Object obj = ref.toObject();
    Offset offset = metaDataA.toOffset();
    int location = metaDataB.toInt();
    Magic.setWordAtOffset(obj, offset, rawTarget, location);
  }

  /**
   * Perform the actual read of the read barrier.
   *
   * @param ref The object that has the reference field
   * @param slot The slot that holds the reference
   * @param metaDataA The offset from the ref
   * @param metaDataB The index of the FieldReference
   * @param mode The context in which the write is occuring
   * @return the read value
   */
  @Inline
  public final ObjectReference performReadInBarrier(ObjectReference ref, Address slot,
                                                    Word metaDataA, Word metaDataB, int mode) {
    Object obj = ref.toObject();
    Offset offset = metaDataA.toOffset();
    int location = metaDataB.toInt();
    return ObjectReference.fromObject(Magic.getObjectAtOffset(obj, offset, location));
  }

  /**
   * Perform the actual read of the read barrier, returning the value as a raw word.
   *
   * @param ref The object that has the reference field
   * @param slot The slot that holds the reference
   * @param metaDataA The offset from the ref
   * @param metaDataB The index of the FieldReference
   * @param mode The context in which the write is occuring
   * @return the read value
   */
  @Inline
  public final Word performRawReadInBarrier(ObjectReference ref, Address slot,
                                            Word metaDataA, Word metaDataB, int mode) {
    Object obj = ref.toObject();
    Offset offset = metaDataA.toOffset();
    int location = metaDataB.toInt();
    return Magic.getWordAtOffset(obj, offset, location);
  }

  /**
   * Atomically write a reference field of an object or array and return
   * the old value of the reference field.
   *
   * @param ref The object that has the reference field
   * @param slot The slot that holds the reference
   * @param target The value that the slot will be updated to
   * @param metaDataA The offset from the ref
   * @param metaDataB Unused
   * @param mode The context in which the write is occuring
   * @return The value that was replaced by the write.
   */
  @Inline
  public final ObjectReference performWriteInBarrierAtomic(
                                           ObjectReference ref, Address slot,
                                           ObjectReference target, Word metaDataA,
                                           Word metaDataB, int mode) {
    Object obj = ref.toObject();
    Object newObject = target.toObject();
    Offset offset = metaDataA.toOffset();
    Object oldObject;
    do {
      oldObject = Magic.prepareObject(obj, offset);
    } while (!Magic.attemptObject(obj, offset, oldObject, newObject));
    return ObjectReference.fromObject(oldObject);
  }


  /**
   * Atomically write a raw reference field of an object or array and return
   * the old value of the reference field.
   *
   * @param ref The object that has the reference field
   * @param slot The slot that holds the reference
   * @param rawTarget The value that the slot will be updated to
   * @param metaDataA The offset from the ref
   * @param metaDataB Unused
   * @param mode The context in which the write is occuring
   * @return The value that was replaced by the write.
   */
  @Inline
  public final Word performRawWriteInBarrierAtomic(
                                           ObjectReference ref, Address slot,
                                           Word rawTarget, Word metaDataA,
                                           Word metaDataB, int mode) {
    Object obj = ref.toObject();
    Offset offset = metaDataA.toOffset();
    Word oldValue;
    do {
      oldValue = Magic.prepareWord(obj, offset);
    } while (!Magic.attemptWord(obj, offset, oldValue, rawTarget));
    return oldValue;
  }

  /**
   * Attempt an atomic compare and exchange in a write barrier sequence.
   *
   * @param ref The object that has the reference field
   * @param slot The slot that holds the reference
   * @param old The old reference to be swapped out
   * @param target The value that the slot will be updated to
   * @param metaDataA The offset from the ref
   * @param metaDataB Unused
   * @param mode The context in which the write is occuring
   * @return True if the compare and swap was successful
   */
  @Inline
  public final boolean tryCompareAndSwapWriteInBarrier(ObjectReference ref, Address slot,
                                                       ObjectReference old, ObjectReference target,
                                                       Word metaDataA, Word metaDataB, int mode) {
    Object oldValue;
    Offset offset = metaDataA.toOffset();
    do {
      oldValue = Magic.prepareObject(ref, offset);
      if (oldValue != old) return false;
    } while (!Magic.attemptObject(ref, offset, oldValue, target));
    return true;
  }


  /**
   * Attempt an atomic compare and exchange in a write barrier sequence.
   *
   * @param ref The object that has the reference field
   * @param slot The slot that holds the reference
   * @param rawOld The old reference to be swapped out
   * @param rawTarget The value that the slot will be updated to
   * @param metaDataA The offset from the ref
   * @param metaDataB Unused
   * @param mode The context in which the write is occuring
   * @return True if the compare and swap was successful
   */
  @Inline
  public final boolean tryRawCompareAndSwapWriteInBarrier(ObjectReference ref, Address slot,
                                                          Word rawOld, Word rawTarget, Word metaDataA,
                                                          Word metaDataB, int mode) {
    Offset offset = metaDataA.toOffset();
    do {
      Word currentValue = Magic.prepareWord(ref, offset);
      if (currentValue != rawOld) return false;
    } while (!Magic.attemptObject(ref, offset, rawOld, rawTarget));
    return true;
  }

  /**
   * Sets an element of an object array without invoking any write
   * barrier.  This method is called by the Map class to ensure
   * potentially-allocation-triggering write barriers do not occur in
   * allocation slow path code.
   *
   * @param dst the destination array
   * @param index the index of the element to set
   * @param value the new value for the element
   */
  public final void setArrayNoBarrier(Object [] dst, int index, Object value) {
    dst[index] = value;
  }
}