Add options for concurrent dcopy

copy.go

@@ -1,12 +1,15 @@
 package copy
 
 import (
+	"context"
 	"io"
 	"io/fs"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"time"
+
+	"golang.org/x/sync/semaphore"
 )
 
 type timespec struct {
@@ -18,6 +21,10 @@ type timespec struct {
 // Copy copies src to dest, doesn't matter if src is a directory or a file.
 func Copy(src, dest string, opts ...Options) error {
 	opt := assureOptions(src, dest, opts...)
+	if opt.NumberOfWorkers > 1 {
+		opt.intent.sem = semaphore.NewWeighted(opt.NumberOfWorkers)
+		opt.intent.ctx = context.Background()
+	}
 	if opt.FS != nil {
 		info, err := fs.Stat(opt.FS, src)
 		if err != nil {

go.mod

@@ -4,5 +4,6 @@ go 1.18
 
 require (
 	github.com/otiai10/mint v1.5.1
+	golang.org/x/sync v0.3.0
 	golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8
 )

go.sum

@@ -1,4 +1,6 @@
 github.com/otiai10/mint v1.5.1 h1:XaPLeE+9vGbuyEHem1JNk3bYc7KKqyI/na0/mLd/Kks=
 github.com/otiai10/mint v1.5.1/go.mod h1:MJm72SBthJjz8qhefc4z1PYEieWmy8Bku7CjcAqyUSM=
+golang.org/x/sync v0.3.0 h1:ftCYgMx6zT/asHUrPw8BLLscYtGznsLAnjq5RH9P66E=
+golang.org/x/sync v0.3.0/go.mod h1:FU7BRWz2tNW+3quACPkgCx/L+uEAv1htQ0V83Z9Rj+Y=
 golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8 h1:0A+M6Uqn+Eje4kHMK80dtF3JCXC4ykBgQG4Fe06QRhQ=
 golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

options.go

@@ -1,9 +1,12 @@
 package copy
 
 import (
+	"context"
 	"io"
 	"io/fs"
 	"os"
+
+	"golang.org/x/sync/semaphore"
 )
 
 // Options specifies optional actions on copying.
@@ -65,10 +68,28 @@ type Options struct {
 	// e.g., You can use embed.FS to copy files from embedded filesystem.
 	FS fs.FS
 
-	intent struct {
-		src  string
-		dest string
-	}
+	// NumberOfWorkers represents the number of workers used for
+	// concurrent copying contents of directories.
+	// If 0 or 1, it does not use goroutine for copying directories.
+	// Please refer to https://pkg.go.dev/golang.org/x/sync/semaphore for more details.
+	NumberOfWorkers int64
+
+	// PreferConcurrent is a function to determine whether or not
+	// to use goroutine for copying contents of directories.
+	// If PreferConcurrent is nil, which is default, it does concurrent
+	// copying for all directories.
+	// If NumberOfWorkers is 0 or 1, this function will be ignored.
+	PreferConcurrent func(srcdir, destdir string) (bool, error)
+
+	// Internal use only
+	intent intent
+}
+
+type intent struct {
+	src  string
+	dest string
+	sem  *semaphore.Weighted
+	ctx  context.Context
 }
 
 // SymlinkAction represents what to do on symlink.
@@ -112,10 +133,7 @@ func getDefaultOptions(src, dest string) Options {
 		PreserveTimes:     false,              // Do not preserve the modification time
 		CopyBufferSize:    0,                  // Do not specify, use default bufsize (32*1024)
 		WrapReader:        nil,                // Do not wrap src files, use them as they are.
-		intent: struct {
-			src  string
-			dest string
-		}{src, dest},
+		intent:            intent{src, dest, nil, nil},
 	}
 }
 
@@ -141,3 +159,13 @@ func assureOptions(src, dest string, opts ...Options) Options {
 	opts[0].intent.dest = defopt.intent.dest
 	return opts[0]
 }
+
+func shouldCopyDirectoryConcurrent(opt Options, srcdir, destdir string) (bool, error) {
+	if opt.NumberOfWorkers <= 1 {
+		return false, nil
+	}
+	if opt.PreferConcurrent == nil {
+		return true, nil
+	}
+	return opt.PreferConcurrent(srcdir, destdir)
+}