Whilst running -Xcheck:jni to check some code I was working
onI came across a large number of warnings about local refs
from one native method :-

WARNING: JNI local refs: 1056, exceeds capacity: 1055
        at sun.font.CFontManager.loadNativeFonts(Native Method)

The source of the problem is below where it accumulates
references to strings and does not free them once they
are passed on to Java code
----
 for (i = 0; i < num; i++) {
        NSString *fontname = [filteredFonts objectAtIndex:i];
        jobject jFontName = JNFNSToJavaString(env, fontname);
        jobject jFontFamilyName =
            JNFNSToJavaString(env, GetFamilyNameForFontName(fontname));

        JNFCallVoidMethod(env, jthis,
                          jm_registerFont, jFontName, jFontFamilyName);
    }
--
The solution is to add this to the loop :-

        (*env)->DeleteLocalRef(env, jFontName);
        (*env)->DeleteLocalRef(env, jFontFamilyName);