Cache Infrastructure

HotPDF provides bounded memory caching plus persistent caches for reusable font subsets and rendered pages

Weighted memory cache

THPDFWeightedCache in HPDFCache owns TObject values, indexes them by AnsiString, and evicts the least recently used values until their combined weight fits MaxBytes

Get and TryGet promote a hit to most recently used and update request statistics
Peek and ContainsKey inspect entries without changing recency or request statistics
Put takes ownership, replaces an existing key in place, and safely accepts the same object again when only its weight changes
Remove frees an entry, while Extract transfers ownership to the caller
Reducing MaxBytes evicts entries immediately, and TrimToBudget exposes the same convergence operation explicitly
Hits, Misses, HitRate, Evictions, Rejections, and Replacements expose cache behaviour, while ResetStatistics starts a new measurement interval
Slot capacity grows geometrically and live entries remain linked in constant-time recency order

Content keys

function HPDFCacheKeyOfBytes(const Bytes: TBytes): AnsiString;
function HPDFCacheKeyOfStream(Stream: TStream): AnsiString;

Both functions return the same lowercase SHA-256 hexadecimal key for the same content

HPDFCacheKeyOfStream hashes without allocating a second full-size byte array, reads seekable streams from position zero, and restores their original position

Persistent font-subset cache

Set THotPDF.FontSubsetCacheFolder to enable reusable TrueType and OpenType subset results while EnableFontSubsetting is active

The key covers the original font bytes, exact used-glyph bitmap, compact or sparse mode, and cache schema version
Both the normal GDI font-store path and the registered Unicode-font finalizer reuse the same cache
Compact PDF/A entries preserve the old-to-new GID map and new glyph count needed by CIDToGIDMap
Entries are validated before use, corrupt entries are removed, and replacement uses an atomic same-directory move
FontSubsetCacheMaxBytes applies immediately and evicts the least recently accessed exact cache files without traversing unrelated folders
GetFontSubsetCacheInfo reports hits, misses, writes, evictions, corruption, rejections, write failures, bytes, and files
ClearFontSubsetCache removes only font-subset entries and abandoned temporary entries from the configured folder

PDF.EnableFontSubsetting := True;
PDF.FontSubsetCacheFolder := 'C:\ProgramData\MyApp\HotPDF\FontSubsets';
PDF.FontSubsetCacheMaxBytes := 256 * 1024 * 1024;

Persistent rendered-page cache

Set THotPDF.RenderCacheFolder to enable the disk tier used after the in-memory rendered-page cache

Page files are keyed by document content, zero-based page index, DPI, effective optional-content visibility, colour intent, and fallback policy
Layer and colour-intent changes select reusable state variants instead of discarding every cached bitmap
PNG and index updates are atomic, and abandoned temporary files are removed during recovery
Page reads refresh page-level recency, while document count, page count, and byte limits evict least recently used data
Reducing a configured limit converges immediately instead of waiting for a later write
Corrupt PNG files, stale or duplicate index rows, missing folders, and unindexed cache folders are repaired automatically
Invalid document keys and coordinates are rejected before filesystem access

Ownership