[Jastadd] Beaver + fullCopy()

From: Jesper Mattsson <jesper.mattsson_at_modelon.com>
Date: Wed, 22 Aug 2012 15:16:33 +0000

Hi

I have found a problem when using the beaver flag to JastAdd. The beaver.Symbol class has a final field value, that in the default constructor is set to this. When using copy() or fullCopy(), then the node is copied using clone(), and thus the value field is set to a reference to the original node. This leads to strange memory leaks, where old nodes are retained because of this field.

We have had huge problems in Eclipse with memory leaks, and changing ASTNode.clone() to set value to this solves those problems. Doing this requires using reflection (since value is final). Here is one way to do that:

  public ASTNode<T> clone() throws CloneNotSupportedException {
    ASTNode node = (ASTNode)super.clone();
    node.in$Circle(false);
    node.is$Final(false);
    try {
           Field f = beaver.Symbol.class.getField("value");
           new ClearFinalFieldAction().perform(f, node);
    } catch (Exception e) {
           e.printStackTrace();
    }
    return node;
  }

  private static class ClearFinalFieldAction implements PrivilegedExceptionAction {
           private Field field;

           public void perform(Field f, Object o) throws Exception {
                      field = f;
                      AccessController.doPrivileged(this);
                      f.set(o, o);
           }

           public Object run() throws Exception {
                      field.setAccessible(true);
                      return null;
           }
  }

Jesper

Jesper MATTSSON, MSc
Software Developer & IT Administrator

Phone direct: +46 73 324 5909
Email: jesper.mattsson_at_modelon.com<mailto:jesper.mattsson_at_modelon.com>

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Received on Wed Aug 22 2012 - 17:17:02 CEST