perf: parallelize genparcelspec across CPU cores

Process Java files concurrently with one ANTLR parser per worker
goroutine. Reduces wall time from 55s to 20s (2.75x speedup)
by utilizing all CPU cores for parsing.

Author: xaionaro@dx.center

tools/cmd/genparcelspec/main.go

@@ -5,8 +5,11 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"runtime"
 	"runtime/pprof"
 	"strings"
+	"sync"
+	"sync/atomic"
 
 	"github.com/xaionaro-go/binder/tools/pkg/parcelspec"
 	"gopkg.in/yaml.v3"
@@ -46,14 +49,21 @@ func main() {
 	}
 }
 
+type fileWork struct {
+	path        string
+	packageName string
+	src         []byte
+}
+
 func run(
 	frameworksBase string,
 	outputDir string,
 ) error {
-	generated := 0
-	skipped := 0
-	extractor := parcelspec.NewJavaExtractor()
+	var generated atomic.Int64
+	var skipped atomic.Int64
 
+	// Collect files to process.
+	var files []fileWork
 	err := filepath.Walk(frameworksBase, func(path string, info os.FileInfo, err error) error {
 		if err != nil {
 			return err
@@ -78,26 +88,56 @@ func run(
 			return nil
 		}
 
-		specs := extractor.ExtractSpecs(string(src), packageName)
-		for _, spec := range specs {
-			if len(spec.Fields) == 0 {
-				skipped++
-				continue
-			}
-
-			if err := writeSpec(outputDir, spec); err != nil {
-				return fmt.Errorf("writing spec for %s.%s: %w", spec.Package, spec.Type, err)
-			}
-			generated++
-		}
-
+		files = append(files, fileWork{path: path, packageName: packageName, src: src})
 		return nil
 	})
 	if err != nil {
 		return fmt.Errorf("walking %s: %w", frameworksBase, err)
 	}
 
-	fmt.Fprintf(os.Stderr, "genparcelspec: generated %d specs, skipped %d empty specs\n", generated, skipped)
+	// Process files in parallel. Each worker has its own ANTLR parser
+	// (not thread-safe), fed from a shared channel.
+	work := make(chan fileWork, len(files))
+	for _, f := range files {
+		work <- f
+	}
+	close(work)
+
+	numWorkers := runtime.NumCPU()
+	var wg sync.WaitGroup
+	var firstErr atomic.Value
+
+	for range numWorkers {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			extractor := parcelspec.NewJavaExtractor()
+
+			for fw := range work {
+				specs := extractor.ExtractSpecs(string(fw.src), fw.packageName)
+				for _, spec := range specs {
+					if len(spec.Fields) == 0 {
+						skipped.Add(1)
+						continue
+					}
+
+					if err := writeSpec(outputDir, spec); err != nil {
+						firstErr.CompareAndSwap(nil, fmt.Errorf("writing spec for %s.%s: %w", spec.Package, spec.Type, err))
+						return
+					}
+					generated.Add(1)
+				}
+			}
+		}()
+	}
+
+	wg.Wait()
+
+	if v := firstErr.Load(); v != nil {
+		return v.(error)
+	}
+
+	fmt.Fprintf(os.Stderr, "genparcelspec: generated %d specs, skipped %d empty specs\n", generated.Load(), skipped.Load())
 	return nil
 }