App Crashes when open & close PDF multiple times

like this:
public void closeForm() {
if (pdfReader != null) {
m_thumb.thumbClose();
pdfReader.PDFClose();
pdfLayer.removeView(pdfReader);
}
pdfReader = null;
m_thumb = null;//??
pdfFile = null;
}
the most important thing is: do not open PDFReader/PDFThumbView and close PDFReader/PDFThumbView in different thread.

12-16 20:43:00.168: A/libc(8457): Fatal signal 11 (SIGSEGV) at 0x0037534b (code=1), thread 10074 (AsyncTask #3)
12-16 20:43:00.258: D/dalvikvm(8457): GC_FOR_ALLOC freed 7729K, 22% free 46498K/59344K, paused 31ms, total 31ms

I have the same situation. (open & close PDF multiple times.)
I changed the library from 3.1 to 3.2.
But it is occured sometimes...

It seems to be fine now to run pdfReader.PDFClose() in the GUI thread same as opening PDF, thank you