Add parallel build support with -parallel and -jobs options

This commit introduces parallel package building to ratt.
- New flag `-parallel` enables parallel builds.
- New flag `-jobs` controls the number of concurrent workers
  (default: number of CPU cores, must be > 0).
- Added `buildPackagesSequential` and `buildPackagesParallel` helpers.
- Refactored main build loop to support sequential or parallel execution.

This allows faster builds by utilizing multiple CPU cores.

Signed-off-by: Arthur Diniz <[email protected]>

Author: arthurbdiniz

go.mod

@@ -1,10 +1,13 @@
 module github.com/Debian/ratt
 
-go 1.18
+go 1.24.0
+
+toolchain go1.24.4
 
 require pault.ag/go/debian v0.12.0
 
 require (
 	golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897 // indirect
+	golang.org/x/sync v0.17.0 // indirect
 	pault.ag/go/topsort v0.0.0-20160530003732-f98d2ad46e1a // indirect
 )

go.sum

@@ -5,6 +5,8 @@ golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACk
 golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897 h1:pLI5jrR7OSLijeIDcmRxNmw2api+jEfxLoykJVice/E=
 golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/sync v0.17.0 h1:l60nONMj9l5drqw6jlhIELNv9I0A4OFgRsG9k2oT9Ug=
+golang.org/x/sync v0.17.0/go.mod h1:9KTHXmSnoGruLpwFjVSX0lNNA75CykiMECbovNTZqGI=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

ratt.go

@@ -21,9 +21,12 @@ import (
 	"os/exec"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"sort"
 	"strings"
+	"sync"
 
+	"golang.org/x/sync/errgroup"
 	"pault.ag/go/debian/control"
 	"pault.ag/go/debian/version"
 )
@@ -100,6 +103,14 @@ var (
 		false,
 		"Output results in JSON format (currently only works in combination with -dry_run)")
 
+	parallel = flag.Bool("parallel",
+		false,
+		"Build packages in parallel")
+
+	jobs = flag.Int("jobs",
+		runtime.NumCPU(),
+		"Number of parallel build jobs (default: number of CPU cores)")
+
 	listsPrefixRe = regexp.MustCompile(`/([^/]*_dists_.*)_InRelease$`)
 )
 
@@ -429,13 +440,91 @@ func getAptIndexPaths(dist string) ([]string, []string) {
 	return fallbackIndexPaths()
 }
 
+type buildJob struct {
+	src     string
+	version version.Version
+}
+
+func buildPackagesSequential(builder *sbuild, rebuild map[string][]version.Version) (map[string]*buildResult, []dryRunBuild) {
+	buildresults := make(map[string]*buildResult)
+	var dryRunBuilds []dryRunBuild
+	cnt := 1
+
+	for src, versions := range rebuild {
+		sort.Sort(sort.Reverse(version.Slice(versions)))
+		newest := versions[0]
+		log.Printf("Building package %d of %d: %s\n", cnt, len(rebuild), src)
+		cnt++
+		result := builder.build(src, &newest)
+		if result.err != nil {
+			log.Printf("building %s failed: %v\n", src, result.err)
+		}
+		buildresults[src] = result
+
+		if *dryRun {
+			cmd := builder.buildCommandLine(src, &newest)
+			dryRunBuilds = append(dryRunBuilds, dryRunBuild{
+				Package:       src,
+				Version:       newest.String(),
+				SbuildCommand: strings.Join(cmd, " "),
+			})
+		}
+	}
+	return buildresults, dryRunBuilds
+}
+
+func buildPackagesParallel(builder *sbuild, rebuild map[string][]version.Version, numJobs int) (map[string]*buildResult, []dryRunBuild) {
+	var eg errgroup.Group
+	eg.SetLimit(numJobs)
+
+	buildresults := make(map[string]*buildResult)
+	var dryRunBuilds []dryRunBuild
+	var resultsMu sync.Mutex
+	cnt := 1
+
+	for src, versions := range rebuild {
+		src, versions := src, versions // capture loop variables
+		eg.Go(func() error {
+			sort.Sort(sort.Reverse(version.Slice(versions)))
+			newest := versions[0]
+			log.Printf("Building package %d of %d: %s\n", cnt, len(rebuild), src)
+			cnt++
+			result := builder.build(src, &newest)
+			if result.err != nil {
+				log.Printf("building %s failed: %v\n", src, result.err)
+			}
+
+			resultsMu.Lock()
+			buildresults[src] = result
+			if *dryRun {
+				cmd := builder.buildCommandLine(src, &newest)
+				dryRunBuilds = append(dryRunBuilds, dryRunBuild{
+					Package:       src,
+					Version:       newest.String(),
+					SbuildCommand: strings.Join(cmd, " "),
+				})
+			}
+			resultsMu.Unlock()
+			return nil
+		})
+	}
+
+	eg.Wait()
+	log.Printf("Completed building %d packages with %d workers\n", len(buildresults), numJobs)
+	return buildresults, dryRunBuilds
+}
+
 func main() {
 	flag.Parse()
 
 	if *jsonOutput && !*dryRun {
 		log.Fatal("-json can only be used together with -dry_run")
 	}
 
+	if *jobs <= 0 {
+		log.Fatal("-jobs must be a positive number")
+	}
+
 	if flag.NArg() == 0 {
 		log.Fatalf("Usage: %s [options] <path-to-changes-file>...\n", os.Args[0])
 	}
@@ -569,28 +658,15 @@ func main() {
 		dryRun:    *dryRun,
 		extraDebs: debs,
 	}
-	cnt := 1
+
 	buildresults := make(map[string](*buildResult))
 	var dryRunBuilds []dryRunBuild
-	for src, versions := range rebuild {
-		sort.Sort(sort.Reverse(version.Slice(versions)))
-		newest := versions[0]
-		log.Printf("Building package %d of %d: %s \n", cnt, len(rebuild), src)
-		cnt++
-		result := builder.build(src, &newest)
-		if result.err != nil {
-			log.Printf("building %s failed: %v\n", src, result.err)
-		}
-		buildresults[src] = result
 
-		if *dryRun {
-			cmd := builder.buildCommandLine(src, &newest)
-			dryRunBuilds = append(dryRunBuilds, dryRunBuild{
-				Package:       src,
-				Version:       newest.String(),
-				SbuildCommand: strings.Join(cmd, " "),
-			})
-		}
+	if *parallel {
+		log.Printf("Building packages in parallel using %d workers\n", *jobs)
+		buildresults, dryRunBuilds = buildPackagesParallel(builder, rebuild, *jobs)
+	} else {
+		buildresults, dryRunBuilds = buildPackagesSequential(builder, rebuild)
 	}
 
 	var toInclude []string