hswg: parallelize rendering

hswg/main.go

@@ -17,6 +17,7 @@ import (
 	"regexp"
 	"sort"
 	"strings"
+	"sync"
 	"syscall"
 	"time"
 
@@ -121,7 +122,7 @@ type Entry struct {
 
 // Published returns the date when the entry was published, or nil if unknown.
 func (e *Entry) Published() *time.Time {
-	if d, _, err := e.Attributes.GetAsString("date"); err != nil {
+	if d, ok, err := e.Attributes.GetAsString("date"); !ok || err != nil {
 		return nil
 	} else if t, err := time.Parse(time.RFC3339, d); err == nil {
 		return &t
@@ -287,14 +288,25 @@ func writeIndex(path string, t *template.Template,
 
 func finalizeEntries(entries *map[string]*Entry, t *template.Template,
 	indexPath string, indexT *template.Template) {
+	// The initial render of a large amount of entries is resource-intensive.
+	var wg sync.WaitGroup
 	for name, e := range *entries {
 		e.backlinks = map[string]bool{}
-		if e.raw == nil {
+		if e.raw != nil {
+			continue
+		}
+
+		wg.Add(1)
+		go func(name string, e *Entry) {
+			defer wg.Done()
 			if err := renderEntry(name, e); err != nil {
 				log.Printf("%s: %s\n", name, err)
 			}
+		}(name, e)
 	}
-	}
+
+	wg.Wait()
+
 	for name, e := range *entries {
 		// Expand LinkWords anywhere between <tags>.
 		// We want something like the inverse of Regexp.ReplaceAllStringFunc.