The counters of a document's render caches, read one cache at a time (CacheStatistics).
public PdfDocumentCacheStatistics(PdfCacheStatistics Content, PdfCacheStatistics Images, PdfCacheStatistics Glyphs, PdfCacheStatistics DisplayLists)
Decoded content streams of pages, form XObjects, patterns and Type 3 glyphs (ContentCacheBudget).
Decoded image XObjects with their masks, and stencil masks (ImageCacheBudget).
Glyph outlines read from font programs (GlyphCacheBudget).
Pages' display lists (DisplayListCacheBudget).
Spec #33 viewer capability 13 and story 8. Each cache is read under its own lock, so while other threads render the four may come from slightly different moments.