Examples with ForwardingWord org.mmtk.utility.ForwardingWord used on opensource projects

Example 1 with ForwardingWord

use of org.mmtk.utility.ForwardingWord in project JikesRVM by JikesRVM.

the class CopySpace method traceObject.

/**
 * Trace an object under a copying collection policy.<p>
 *
 * We use a tri-state algorithm to deal with races to forward
 * the object.  The tracer must wait if the object is concurrently
 * being forwarded by another thread.<p>
 *
 * If the object is already forwarded, the copy is returned.
 * Otherwise, the object is forwarded and the copy is returned.
 *
 * @param trace The trace being conducted.
 * @param object The object to be forwarded.
 * @param allocator The allocator to use when copying.
 * @return The forwarded object.
 */
@Inline
public ObjectReference traceObject(TransitiveClosure trace, ObjectReference object, int allocator) {
    /* If the object in question is already in to-space, then do nothing */
    if (!fromSpace)
        return object;
    /* Try to forward the object */
    Word forwardingWord = ForwardingWord.attemptToForward(object);
    if (ForwardingWord.stateIsForwardedOrBeingForwarded(forwardingWord)) {
        /* We must wait (spin) if the object is not yet fully forwarded */
        while (ForwardingWord.stateIsBeingForwarded(forwardingWord)) forwardingWord = VM.objectModel.readAvailableBitsWord(object);
        /* Now extract the object reference from the forwarding word and return it */
        return ForwardingWord.extractForwardingPointer(forwardingWord);
    } else {
        /* We are the designated copier, so forward it and enqueue it */
        ObjectReference newObject = VM.objectModel.copy(object, allocator);
        ForwardingWord.setForwardingPointer(object, newObject);
        // Scan it later
        trace.processNode(newObject);
        if (VM.VERIFY_ASSERTIONS && Options.verbose.getValue() >= 9) {
            Log.write("C[");
            Log.write(object);
            Log.write("/");
            Log.write(getName());
            Log.write("] -> ");
            Log.write(newObject);
            Log.write("/");
            Log.write(Space.getSpaceForObject(newObject).getName());
            Log.writeln("]");
        }
        return newObject;
    }
}