Workaround for LineBreakMeasurer thread safety issues?

Question

Basically, we have a servlet that returns a png in response to a GET request containing a String, and info on the font, size, size of area the text needs to fit in, and color to render it in. Periodically the webserver locks up as requests get stuck in the servlet!
After digging around, I found out that Graphics 2D ops are safe, as long as each thread has it's own instance. No problem there!
The problem is, we want to break the string, and make it fit inside the area given. And it turns out, LineBreakMeasurer eventually calls the method getEngine() on SunLayoutEngine, and threads lock up in there.
Here's the code from SUN:
SunLayoutEngine extract listed below
public final class SunLayoutEngine implements LayoutEngine, LayoutEngineFactory {
    private static native void initGVIDs();
    static {
     initGVIDs();
    private LayoutEngineKey key;
    private static LayoutEngineFactory instance;
    public static LayoutEngineFactory instance() {
        if (instance == null) {
            instance = new SunLayoutEngine();
        return instance;
    private SunLayoutEngine() {
        // actually a factory, key is null so layout cannot be called on it
    public LayoutEngine getEngine(Font2D font, int script, int lang) {
        return getEngine(new LayoutEngineKey(font, script, lang));
  // !!! don't need this unless we have more than one sun layout engine...
    public LayoutEngine getEngine(LayoutEngineKey key) {
        HashMap cache = (HashMap)cacheref.get();
        if (cache == null) {
            cache = new HashMap();
            cacheref = new SoftReference(cache);
        *HERE IS WHERE WE LOCKUP VVV*
        LayoutEngine e = (LayoutEngine)cache.get(key);
        if (e == null) {
            e = new SunLayoutEngine(key.copy());
            cache.put(key, e);
        return e;
    private SoftReference cacheref = new SoftReference(null);
    private SunLayoutEngine(LayoutEngineKey key) {
        this.key = key;
    public void layout(FontStrikeDesc desc, float[] mat, int gmask,
                       int baseIndex, TextRecord tr, boolean rtl, Point2D.Float pt, GVData data) {
        Font2D font = key.font();
        FontStrike strike = font.getStrike(desc);
        nativeLayout(font, strike, mat, gmask, baseIndex, tr.text, tr.start, tr.limit, tr.min, tr.max, key.script(), key.lang(), rtl, pt, data);
    private static native void nativeLayout(Font2D font, FontStrike strike, float[] mat, int gmask, int baseIndex,
                                            char[] chars, int offset, int limit, int min, int max,
                                            int script, int lang, boolean rtl, Point2D.Float pt, GVData data);
}Even though each thread is using it's own LBM instance, they will often lock up inside SunLayoutEngine.
Note the factory method always returns the same instance, which will be shared by all threads!
I've filed a bug against sun. I am open to any workarounds you may have.
And for those of you using various java based report generators, and getting lockups, I think this may be related. :)
Edited by: djoyce on Oct 16, 2007 2:12 PM
Edited by: djoyce on Oct 16, 2007 2:15 PM

Answer 1

Okay, this class is it's own factory, and only one instance is ever created. GlyphLayout calls instance(), and getEngine on that, and then all the threads pile up in the weakref'd hashmap.
at java.util.HashMap.get(HashMap.java:348)
at sun.font.SunLayoutEngine.getEngine(SunLayoutEngine.java:113)
at sun.font.GlyphLayout$EngineRecord.init(GlyphLayout.java:565)
at sun.font.GlyphLayout.nextEngineRecord(GlyphLayout.java:439)
at sun.font.GlyphLayout.layout(GlyphLayout.java:371)
at sun.font.ExtendedTextSourceLabel.createGV(ExtendedTextSourceLabel.java:267)
at sun.font.ExtendedTextSourceLabel.getGV(ExtendedTextSourceLabel.java:252)
at sun.font.ExtendedTextSourceLabel.createCharinfo(ExtendedTextSourceLabel.java:522)
at sun.font.ExtendedTextSourceLabel.getCharinfo(ExtendedTextSourceLabel.java:451)
at sun.font.ExtendedTextSourceLabel.getLineBreakIndex(ExtendedTextSourceLabel.java:397)
at java.awt.font.TextMeasurer.calcLineBreak(TextMeasurer.java:313)
at java.awt.font.TextMeasurer.getLineBreakIndex(TextMeasurer.java:548)
at java.awt.font.LineBreakMeasurer.nextOffset(LineBreakMeasurer.java:340)
at java.awt.font.LineBreakMeasurer.nextLayout(LineBreakMeasurer.java:422)
at java.awt.font.LineBreakMeasurer.nextLayout(LineBreakMeasurer.java:395)