Fix semaphore acquisition order

Acquire semaphore before spawning goroutine in calculateDirSizeFast to prevent goroutine
explosion. Previously, all subdirectory goroutines were spawned immediately and blocked on
the semaphore—now the spawning itself is throttled.

cmd/analyze/scanner.go

@@ -126,10 +126,10 @@ func scanPathConcurrent(root string, filesScanned, dirsScanned, bytesScanned *in
 
 			// ~/Library is scanned separately; reuse cache when possible.
 			if isHomeDir && child.Name() == "Library" {
+				sem <- struct{}{}
 				wg.Add(1)
 				go func(name, path string) {
 					defer wg.Done()
-					sem <- struct{}{}
 					defer func() { <-sem }()
 
 					var size int64
@@ -156,10 +156,10 @@ func scanPathConcurrent(root string, filesScanned, dirsScanned, bytesScanned *in
 
 			// Folded dirs: fast size without expanding.
 			if shouldFoldDirWithPath(child.Name(), fullPath) {
+				sem <- struct{}{}
 				wg.Add(1)
 				go func(name, path string) {
 					defer wg.Done()
-					sem <- struct{}{}
 					defer func() { <-sem }()
 
 					size, err := getDirectorySizeFromDu(path)
@@ -180,10 +180,10 @@ func scanPathConcurrent(root string, filesScanned, dirsScanned, bytesScanned *in
 				continue
 			}
 
+			sem <- struct{}{}
 			wg.Add(1)
 			go func(name, path string) {
 				defer wg.Done()
-				sem <- struct{}{}
 				defer func() { <-sem }()
 
 				size := calculateDirSizeConcurrent(path, largeFileChan, filesScanned, dirsScanned, bytesScanned, currentPath)
@@ -311,11 +311,11 @@ func calculateDirSizeFast(root string, filesScanned, dirsScanned, bytesScanned *
 
 		for _, entry := range entries {
 			if entry.IsDir() {
-				wg.Add(1)
 				subDir := filepath.Join(dirPath, entry.Name())
+				sem <- struct{}{}
+				wg.Add(1)
 				go func(p string) {
 					defer wg.Done()
-					sem <- struct{}{}
 					defer func() { <-sem }()
 					walk(p)
 				}(subDir)
@@ -446,9 +446,11 @@ func calculateDirSizeConcurrent(root string, largeFileChan chan<- fileEntry, fil
 
 		if child.IsDir() {
 			if shouldFoldDirWithPath(child.Name(), fullPath) {
+				sem <- struct{}{}
 				wg.Add(1)
 				go func(path string) {
 					defer wg.Done()
+					defer func() { <-sem }()
 					size, err := getDirectorySizeFromDu(path)
 					if err == nil && size > 0 {
 						atomic.AddInt64(&total, size)
@@ -459,10 +461,10 @@ func calculateDirSizeConcurrent(root string, largeFileChan chan<- fileEntry, fil
 				continue
 			}
 
+			sem <- struct{}{}
 			wg.Add(1)
 			go func(path string) {
 				defer wg.Done()
-				sem <- struct{}{}
 				defer func() { <-sem }()
 
 				size := calculateDirSizeConcurrent(path, largeFileChan, filesScanned, dirsScanned, bytesScanned, currentPath)