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feat: introduce a LRU compiled style cache for the HTML formatter #938

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merged 1 commit into from
Feb 27, 2024
Merged

feat: introduce a LRU compiled style cache for the HTML formatter #938

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69 changes: 62 additions & 7 deletions formatters/html/html.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ import (
"sort"
"strconv"
"strings"
"sync"

"github.com/alecthomas/chroma/v2"
)
Expand Down Expand Up @@ -133,6 +134,7 @@ func New(options ...Option) *Formatter {
baseLineNumber: 1,
preWrapper: defaultPreWrapper,
}
f.styleCache = newStyleCache(f)
for _, option := range options {
option(f)
}
Expand Down Expand Up @@ -189,6 +191,7 @@ var (

// Formatter that generates HTML.
type Formatter struct {
styleCache *styleCache
standalone bool
prefix string
Classes bool // Exported field to detect when classes are being used
Expand Down Expand Up @@ -221,12 +224,7 @@ func (f *Formatter) Format(w io.Writer, style *chroma.Style, iterator chroma.Ite
//
// OTOH we need to be super careful about correct escaping...
func (f *Formatter) writeHTML(w io.Writer, style *chroma.Style, tokens []chroma.Token) (err error) { // nolint: gocyclo
css := f.styleToCSS(style)
if !f.Classes {
for t, style := range css {
css[t] = compressStyle(style)
}
}
css := f.styleCache.get(style)
if f.standalone {
fmt.Fprint(w, "<html>\n")
if f.Classes {
Expand Down Expand Up @@ -420,7 +418,7 @@ func (f *Formatter) tabWidthStyle() string {

// WriteCSS writes CSS style definitions (without any surrounding HTML).
func (f *Formatter) WriteCSS(w io.Writer, style *chroma.Style) error {
css := f.styleToCSS(style)
css := f.styleCache.get(style)
// Special-case background as it is mapped to the outer ".chroma" class.
if _, err := fmt.Fprintf(w, "/* %s */ .%sbg { %s }\n", chroma.Background, f.prefix, css[chroma.Background]); err != nil {
return err
Expand Down Expand Up @@ -563,3 +561,60 @@ func compressStyle(s string) string {
}
return strings.Join(out, ";")
}

const styleCacheLimit = 16

type styleCacheEntry struct {
style *chroma.Style
cache map[chroma.TokenType]string
}

type styleCache struct {
mu sync.Mutex
// LRU cache of compiled (and possibly compressed) styles. This is a slice
// because the cache size is small, and a slice is sufficiently fast for
// small N.
cache []styleCacheEntry
f *Formatter
}

func newStyleCache(f *Formatter) *styleCache {
return &styleCache{f: f}
}

func (l *styleCache) get(style *chroma.Style) map[chroma.TokenType]string {
l.mu.Lock()
defer l.mu.Unlock()
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@gkaikoponen gkaikoponen Feb 27, 2024 •
edited
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Can this be turned into a sync.RWLock? Most cases will probably only write to this cache once so it'd be a shame to introduce potential lock-contention if there are many reads.

Something like https://stackoverflow.com/a/70236841 should dodge the gotchas with finishing the read-unlock-defer before grabbing the write lock

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Possibly, send a PR through if you're interested.

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FWIW I started with an RWMutex but it simplifies the code being a plain Mutex.


// Look for an existing entry.
for i := len(l.cache) - 1; i >= 0; i-- {
entry := l.cache[i]
if entry.style == style {
// Top of the cache, no need to adjust the order.
if i == len(l.cache)-1 {
return entry.cache
}
// Move this entry to the end of the LRU
copy(l.cache[i:], l.cache[i+1:])
l.cache[len(l.cache)-1] = entry
return entry.cache
}
}

// No entry, create one.
cached := l.f.styleToCSS(style)
if !l.f.Classes {
for t, style := range cached {
cached[t] = compressStyle(style)
}
}
for t, style := range cached {
cached[t] = compressStyle(style)
}
// Evict the oldest entry.
if len(l.cache) >= styleCacheLimit {
l.cache = l.cache[0:copy(l.cache, l.cache[1:])]
}
l.cache = append(l.cache, styleCacheEntry{style: style, cache: cached})
return cached
}
19 changes: 16 additions & 3 deletions formatters/html/html_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -222,7 +222,7 @@ func TestTableLinkeableLineNumbers(t *testing.T) {

assert.Contains(t, buf.String(), `id="line1"><a class="lnlinks" href="#line1">1</a>`)
assert.Contains(t, buf.String(), `id="line5"><a class="lnlinks" href="#line5">5</a>`)
assert.Contains(t, buf.String(), `/* LineLink */ .chroma .lnlinks { outline: none; text-decoration: none; color: inherit }`, buf.String())
assert.Contains(t, buf.String(), `/* LineLink */ .chroma .lnlinks { outline:none;text-decoration:none;color:inherit }`, buf.String())
}

func TestTableLineNumberSpacing(t *testing.T) {
Expand Down Expand Up @@ -351,12 +351,25 @@ func TestReconfigureOptions(t *testing.T) {
}

func TestWriteCssWithAllClasses(t *testing.T) {
formatter := New()
formatter.allClasses = true
formatter := New(WithAllClasses(true))

var buf bytes.Buffer
err := formatter.WriteCSS(&buf, styles.Fallback)

assert.NoError(t, err)
assert.NotContains(t, buf.String(), ".chroma . {", "Generated css doesn't contain invalid css")
}

func TestStyleCache(t *testing.T) {
f := New()

assert.True(t, len(styles.Registry) > styleCacheLimit)

for _, style := range styles.Registry {
var buf bytes.Buffer
err := f.WriteCSS(&buf, style)
assert.NoError(t, err)
}

assert.Equal(t, styleCacheLimit, len(f.styleCache.cache))
}