Addressing Marc Antoine's comments

go/pkg/diskcache/diskcache.go

@@ -16,6 +16,8 @@ import (
 	"time"
 
 	"github.com/bazelbuild/remote-apis-sdks/go/pkg/digest"
+	"golang.org/x/sync/errgroup"
+
 	log "github.com/golang/glog"
 )
 
@@ -100,7 +102,7 @@ type DiskCache struct {
 	testGcTicks      chan uint64
 }
 
-func New(ctx context.Context, root string, maxCapacityBytes uint64) *DiskCache {
+func New(ctx context.Context, root string, maxCapacityBytes uint64) (*DiskCache, error) {
 	res := &DiskCache{
 		root:             root,
 		maxCapacityBytes: maxCapacityBytes,
@@ -112,44 +114,45 @@ func New(ctx context.Context, root string, maxCapacityBytes uint64) *DiskCache {
 		shutdown: make(chan bool),
 	}
 	heap.Init(res.queue)
-	_ = os.MkdirAll(root, os.ModePerm)
+	if err := os.MkdirAll(root, os.ModePerm); err != nil {
+		return nil, err
+	}
 	// We use Git's directory/file naming structure as inspiration:
 	// https://git-scm.com/book/en/v2/Git-Internals-Git-Objects#:~:text=The%20subdirectory%20is%20named%20with%20the%20first%202%20characters%20of%20the%20SHA%2D1%2C%20and%20the%20filename%20is%20the%20remaining%2038%20characters.
-	var wg sync.WaitGroup
-	wg.Add(256)
+	eg, eCtx := errgroup.WithContext(ctx)
 	for i := 0; i < 256; i++ {
 		prefixDir := filepath.Join(root, fmt.Sprintf("%02x", i))
-		go func() {
-			defer wg.Done()
-			_ = os.MkdirAll(prefixDir, os.ModePerm)
-			_ = filepath.WalkDir(prefixDir, func(path string, d fs.DirEntry, err error) error {
+		eg.Go(func() error {
+			if eCtx.Err() != nil {
+				return eCtx.Err()
+			}
+			if err := os.MkdirAll(prefixDir, os.ModePerm); err != nil {
+				return err
+			}
+			return filepath.WalkDir(prefixDir, func(path string, d fs.DirEntry, err error) error {
 				// We log and continue on all errors, because cache read errors are not critical.
 				if err != nil {
-					log.Errorf("Error reading cache directory: %v", err)
-					return nil
+					return fmt.Errorf("error reading cache directory: %v", err)
 				}
 				if d.IsDir() {
 					return nil
 				}
 				subdir := filepath.Base(filepath.Dir(path))
 				k, err := res.getKeyFromFileName(subdir + d.Name())
 				if err != nil {
-					log.Errorf("Error parsing cached file name %s: %v", path, err)
-					return nil
+					return fmt.Errorf("error parsing cached file name %s: %v", path, err)
 				}
-				atime, err := GetLastAccessTime(path)
+				atime, err := getLastAccessTime(path)
 				if err != nil {
-					log.Errorf("Error getting last accessed time of %s: %v", path, err)
-					return nil
+					return fmt.Errorf("error getting last accessed time of %s: %v", path, err)
 				}
 				it := &qitem{
 					key: k,
 					lat: atime,
 				}
 				size, err := res.getItemSize(k)
 				if err != nil {
-					log.Errorf("Error getting file size of %s: %v", path, err)
-					return nil
+					return fmt.Errorf("error getting file size of %s: %v", path, err)
 				}
 				res.store.Store(k, it)
 				atomic.AddInt64(&res.sizeBytes, size)
@@ -158,11 +161,13 @@ func New(ctx context.Context, root string, maxCapacityBytes uint64) *DiskCache {
 				res.mu.Unlock()
 				return nil
 			})
-		}()
+		})
+	}
+	if err := eg.Wait(); err != nil {
+		return nil, err
 	}
-	wg.Wait()
 	go res.gc()
-	return res
+	return res, nil
 }
 
 func (d *DiskCache) getItemSize(k key) (int64, error) {
@@ -284,18 +289,13 @@ func copyFile(src, dst string, size int64) error {
 		return err
 	}
 	defer out.Close()
-	_, err = io.Copy(out, in)
+	n, err := io.Copy(out, in)
 	if err != nil {
 		return err
 	}
-	// Required sanity check: sometimes the copy pretends to succeed, but doesn't, if
-	// the file is being concurrently deleted.
-	dstInfo, err := os.Stat(dst)
-	if err != nil {
-		return err
-	}
-	if dstInfo.Size() != size {
-		return fmt.Errorf("copy of %s to %s failed: src/dst size mismatch: wanted %d, got %d", src, dst, size, dstInfo.Size())
+	// Required sanity check: if the file is being concurrently deleted, we may not always copy everything.
+	if n != size {
+		return fmt.Errorf("copy of %s to %s failed: src/dst size mismatch: wanted %d, got %d", src, dst, size, n)
 	}
 	return nil
 }
@@ -309,15 +309,23 @@ func (d *DiskCache) LoadCas(dg digest.Digest, path string) bool {
 	}
 	it := iUntyped.(*qitem)
 	it.mu.RLock()
-	if err := copyFile(d.getPath(k), path, dg.Size); err != nil {
+	err := copyFile(d.getPath(k), path, dg.Size)
+	it.mu.RUnlock()
+	if err != nil {
 		// It is not possible to prevent a race with GC; hence, we return false on copy errors.
-		it.mu.RUnlock()
 		return false
 	}
-	it.mu.RUnlock()
 
 	d.mu.Lock()
 	d.queue.Bump(it)
 	d.mu.Unlock()
 	return true
 }
+
+func getLastAccessTime(path string) (time.Time, error) {
+	info, err := os.Stat(path)
+	if err != nil {
+		return time.Time{}, err
+	}
+	return FileInfoToAccessTime(info), nil
+}

go/pkg/diskcache/diskcache_test.go

@@ -41,7 +41,10 @@ func TestStoreLoadCasPerm(t *testing.T) {
 	for _, tc := range tests {
 		t.Run(tc.name, func(t *testing.T) {
 			root := t.TempDir()
-			d := New(context.Background(), filepath.Join(root, "cache"), 20)
+			d, err := New(context.Background(), filepath.Join(root, "cache"), 20)
+			if err != nil {
+				t.Errorf("New: %v", err)
+			}
 			defer d.Shutdown()
 			fname, _ := testutil.CreateFile(t, tc.executable, "12345")
 			srcInfo, err := os.Stat(fname)
@@ -79,7 +82,10 @@ func TestStoreLoadCasPerm(t *testing.T) {
 
 func TestLoadCasNotFound(t *testing.T) {
 	root := t.TempDir()
-	d := New(context.Background(), filepath.Join(root, "cache"), 20)
+	d, err := New(context.Background(), filepath.Join(root, "cache"), 20)
+	if err != nil {
+		t.Errorf("New: %v", err)
+	}
 	defer d.Shutdown()
 	newName := filepath.Join(root, "new")
 	dg := digest.NewFromBlob([]byte("bla"))
@@ -90,7 +96,10 @@ func TestLoadCasNotFound(t *testing.T) {
 
 func TestGcOldestCas(t *testing.T) {
 	root := t.TempDir()
-	d := New(context.Background(), filepath.Join(root, "cache"), 20)
+	d, err := New(context.Background(), filepath.Join(root, "cache"), 20)
+	if err != nil {
+		t.Errorf("New: %v", err)
+	}
 	defer d.Shutdown()
 	d.testGcTicks = make(chan uint64, 1)
 	for i := 0; i < 5; i++ {
@@ -123,11 +132,11 @@ func TestGcOldestCas(t *testing.T) {
 func isSystemLastAccessTimeAccurate(t *testing.T) bool {
 	t.Helper()
 	fname, _ := testutil.CreateFile(t, false, "foo")
-	lat, _ := GetLastAccessTime(fname)
+	lat, _ := getLastAccessTime(fname)
 	if _, err := os.ReadFile(fname); err != nil {
 		t.Fatalf("%v", err)
 	}
-	newLat, _ := GetLastAccessTime(fname)
+	newLat, _ := getLastAccessTime(fname)
 	return lat.Before(newLat)
 }
 
@@ -140,7 +149,10 @@ func TestInitFromExistingCas(t *testing.T) {
 		return
 	}
 	root := t.TempDir()
-	d := New(context.Background(), filepath.Join(root, "cache"), 20)
+	d, err := New(context.Background(), filepath.Join(root, "cache"), 20)
+	if err != nil {
+		t.Errorf("New: %v", err)
+	}
 	for i := 0; i < 4; i++ {
 		fname, _ := testutil.CreateFile(t, false, fmt.Sprintf("aaa %d", i))
 		dg, err := digest.NewFromFile(fname)
@@ -159,7 +171,10 @@ func TestInitFromExistingCas(t *testing.T) {
 	d.Shutdown()
 
 	// Re-initialize from existing files.
-	d = New(context.Background(), filepath.Join(root, "cache"), 20)
+	d, err = New(context.Background(), filepath.Join(root, "cache"), 20)
+	if err != nil {
+		t.Errorf("New: %v", err)
+	}
 	defer d.Shutdown()
 	d.testGcTicks = make(chan uint64, 1)
 
@@ -169,7 +184,7 @@ func TestInitFromExistingCas(t *testing.T) {
 		t.Errorf("expected %s to be cached", dg)
 	}
 	fname, _ := testutil.CreateFile(t, false, "aaa 4")
-	dg, err := digest.NewFromFile(fname)
+	dg, err = digest.NewFromFile(fname)
 	if err != nil {
 		t.Fatalf("digest.NewFromFile failed: %v", err)
 	}
@@ -198,7 +213,10 @@ func TestThreadSafetyCas(t *testing.T) {
 	nFiles := 10
 	attempts := 5000
 	// All blobs are size 5 exactly. We will have half the byte capacity we need.
-	d := New(context.Background(), filepath.Join(root, "cache"), uint64(nFiles*5)/2)
+	d, err := New(context.Background(), filepath.Join(root, "cache"), uint64(nFiles*5)/2)
+	if err != nil {
+		t.Errorf("New: %v", err)
+	}
 	d.testGcTicks = make(chan uint64, attempts)
 	defer d.Shutdown()
 	var files []string

go/pkg/diskcache/sys_darwin.go

@@ -2,15 +2,11 @@
 package diskcache
 
 import (
-	"os"
+	"io/fs"
 	"syscall"
 	"time"
 )
 
-func GetLastAccessTime(path string) (time.Time, error) {
-	info, err := os.Stat(path)
-	if err != nil {
-		return time.Time{}, err
-	}
-	return time.Unix(info.Sys().(*syscall.Stat_t).Atimespec.Unix()), nil
+func FileInfoToAccessTime(info fs.FileInfo) time.Time {
+	return time.Unix(info.Sys().(*syscall.Stat_t).Atimespec.Unix())
 }

go/pkg/diskcache/sys_linux.go

@@ -2,15 +2,11 @@
 package diskcache
 
 import (
-	"os"
+	"io/fs"
 	"syscall"
 	"time"
 )
 
-func GetLastAccessTime(path string) (time.Time, error) {
-	info, err := os.Stat(path)
-	if err != nil {
-		return time.Time{}, err
-	}
-	return time.Unix(info.Sys().(*syscall.Stat_t).Atim.Unix()), nil
+func FileInfoToAccessTime(info fs.FileInfo) time.Time {
+	return time.Unix(info.Sys().(*syscall.Stat_t).Atim.Unix())
 }

go/pkg/diskcache/sys_windows.go

@@ -2,17 +2,13 @@
 package diskcache
 
 import (
-	"os"
+	"io/fs"
 	"syscall"
 	"time"
 )
 
 // This will return correct values only if `fsutil behavior set disablelastaccess 0` is set.
 // Tracking of last access time is disabled by default on Windows.
-func GetLastAccessTime(path string) (time.Time, error) {
-	info, err := os.Stat(path)
-	if err != nil {
-		return time.Time{}, err
-	}
-	return time.Unix(0, info.Sys().(*syscall.Win32FileAttributeData).LastAccessTime.Nanoseconds()), nil
+func FileInfoToAccessTime(info fs.FileInfo) time.Time {
+	return time.Unix(0, info.Sys().(*syscall.Win32FileAttributeData).LastAccessTime.Nanoseconds())
 }