JNI code in the font manager caches JNIEnv and it may be saved by one thread and reused
by another. This may cause crash.

The 'font2D' jobject needs to be converted into a global reference because its lifetime exceeds the lifetime of a native method call.

This is applicable at least to Freetype glue code.

Here is sample stacktrace from the crash:

Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x298366]
C [libfontmanager.so+0x59e4]
C [libfreetype.so.6+0x73c9] FT_Stream_Close+0x19
C [libfreetype.so.6+0xa065] FT_Stream_Free+0x25
C [libfreetype.so.6+0xa6e2]
C [libfreetype.so.6+0xaf78] FT_Done_Face+0x78
C [libfontmanager.so+0x6964]
Java_sun_font_FreetypeFontScaler_disposeNativeScaler+0x34