Re: Out of memory with file streams

Zig <>
Mon, 17 Mar 2008 17:38:11 -0400
On Mon, 17 Mar 2008 14:15:39 -0400, Hendrik Maryns
<> wrote:

Zig schreef:

On Mon, 17 Mar 2008 07:46:06 -0400, Hendrik Maryns
<> wrote:

Hi all,

I have little proggie that queries large linguistic corpora. To make
the data searchable, I do some preprocessing on the corpus file. I now
start getting into trouble when those files are big. Big means over 40
MB, which isn2"t even that big, come to think of it.

So I am on the lookout for a memory leak, however, I can2"t find it.
preprocessing method basically does the following (suppose the inFile
and the treeFile are given Files):

final BufferedReader corpus = new BufferedReader(new
final ObjectOutputStream treeOut = new ObjectOutputStream(new
BufferedOutputStream(new FileOutputStream(treeFile)));
final int nbTrees = TreebankConverter.parseNegraTrees(corpus, treeOut);
try {
} catch (final IOException e) {
    // if it cannot be closed, it wasn2"t open
try {
} catch (final IOException e) {
    // if it cannot be closed, it wasn2"t open

parseNegraTrees then does the following: it scans through the input
file, constructs trees that are described in it in some text format
(NEGRA), converts those trees to a binary format, and writes them as
Java objects to the treeFile. Each of those trees consists of nodes
with a left daughter, a right daughter and a list of strings of length
at most 5. And those are short strings: words or abbreviations. So
this shouldn2"t take too much memory, I would think.

This is also done one by one:

String bosLine;
while ((bosLine = corpus.readLine()) != null) {
  final StringTokenizer tokens = new StringTokenizer(bosLine);
  final String treeIdLine = tokens.nextToken();
  if (!treeIdLine.equals("%%")) {
   final String treeId = tokens.nextToken();
   final NodeSet forest = parseSentenceNodes(corpus);
   final Node root = forest.toTree();
   final BinaryNode binRoot = root.toBinaryTree(new ArrayList<Node>(),
   final BinaryTree binTree = new BinaryTree(binRoot, treeId);

I see no reason in the above code why the GC wouldn2"t discard the trees
that have been constructed before.

So the only place for memory problems I see here is the file access.
However, as I grasp from the Javadocs, both FileReader and
FileOutputStream are, indeed streams, that do not have to remember what
came before. Is the buffering the problem, maybe?

You are right, FileOutputStream & FileReader are pretty primitive.
ObjectOutputStream, OTOH is a different matter. ObjectOutputStream will
keep references to objects written to the stream, which enables it to
handle cyclic object graphs, and repeating references of the same object
are handled predictably.

You can force ObjectOutputStream to clean up by using:


This should notify ObjectOutputStream that you will not be
re-referencing any previously written objects, and allow the stream to
release it's internal references.

That2"s exactly what I needed. The API could have been more informing
over the memory implications of this backreferencing mechanism. The
memory footprint is not even mentioned in the Javadoc of the reset()

Glad to help!

Thank you very much!

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