operations: enable multi threaded downloads - Fixes #2252

This implements the --multi-thread-cutoff and --multi-thread-streams
flags to control multi thread downloading to the local backend.

README.md

@@ -73,6 +73,7 @@ Please see [the full list of all storage providers and their features](https://r
   * Optional encryption ([Crypt](https://rclone.org/crypt/))
   * Optional cache ([Cache](https://rclone.org/cache/))
   * Optional FUSE mount ([rclone mount](https://rclone.org/commands/rclone_mount/))
+  * Multi-threaded downloads to local disk
 
 ## Installation & documentation
 

docs/content/about.md

@@ -65,6 +65,7 @@ Features
   * ([Cache](/cache/)) backend
   * ([Union](/union/)) backend
   * Optional FUSE mount ([rclone mount](/commands/rclone_mount/))
+  * Multi-threaded downloads to local disk
 
 Links
 

docs/content/docs.md

@@ -674,6 +674,49 @@ if you are reading and writing to an OS X filing system this will be
 
 This command line flag allows you to override that computed default.
 
+### --multi-thread-cutoff=SIZE ###
+
+When downloading files to the local backend above this size, rclone
+will use multiple threads to download the file. (default 250M)
+
+Rclone preallocates the file (using `fallocate(FALLOC_FL_KEEP_SIZE)`
+on unix or `NTSetInformationFile` on Windows both of which takes no
+time) then each thread writes directly into the file at the correct
+place.  This means that rclone won't create fragmented or sparse files
+and there won't be any assembly time at the end of the transfer.
+
+The number of threads used to dowload is controlled by
+`--multi-thread-streams`.
+
+Use `-vv` if you wish to see info about the threads.
+
+This will work with the `sync`/`copy`/`move` commands and friends
+`copyto`/`moveto`.  Multi thread downloads will be used with `rclone
+mount` and `rclone serve` if `--vfs-cache-mode` is set to `writes` or
+above.
+
+**NB** that this **only** works for a local destination but will work
+with any source.
+
+### --multi-thread-streams=N ###
+
+When using multi thread downloads (see above `--multi-thread-cutoff`)
+this sets the maximum number of streams to use.  Set to `0` to disable
+multi thread downloads. (Default 4)
+
+Exactly how many streams rclone uses for the download depends on the
+size of the file. To calculate the number of download streams Rclone
+divides the size of the file by the `--multi-thread-cutoff` and rounds
+up, up to the maximum set with `--multi-thread-streams`.
+
+So if `--multi-thread-cutoff 250MB` and `--multi-thread-streams 4` are
+in effect (the defaults):
+
+- 0MB.250MB files will be downloaded with 1 stream
+- 250MB..500MB files will be downloaded with 2 streams
+- 500MB..750MB files will be downloaded with 3 streams
+- 750MB+ files will be downloaded with 4 streams
+
 ### --no-gzip-encoding ###
 
 Don't set `Accept-Encoding: gzip`.  This means that rclone won't ask

fs/config.go

@@ -93,6 +93,8 @@ type ConfigInfo struct {
 	CaCert                 string // Client Side CA
 	ClientCert             string // Client Side Cert
 	ClientKey              string // Client Side Key
+	MultiThreadCutoff      SizeSuffix
+	MultiThreadStreams     int
 }
 
 // NewConfig creates a new config with everything set to the default
@@ -124,6 +126,8 @@ func NewConfig() *ConfigInfo {
 	c.MaxBacklog = 10000
 	// We do not want to set the default here. We use this variable being empty as part of the fall-through of options.
 	//	c.StatsOneLineDateFormat = "2006/01/02 15:04:05 - "
+	c.MultiThreadCutoff = SizeSuffix(250 * 1024 * 1024)
+	c.MultiThreadStreams = 4
 
 	return c
 }

fs/config/configflags/configflags.go

@@ -95,6 +95,8 @@ func AddFlags(flagSet *pflag.FlagSet) {
 	flags.StringVarP(flagSet, &fs.Config.CaCert, "ca-cert", "", fs.Config.CaCert, "CA certificate used to verify servers")
 	flags.StringVarP(flagSet, &fs.Config.ClientCert, "client-cert", "", fs.Config.ClientCert, "Client SSL certificate (PEM) for mutual TLS auth")
 	flags.StringVarP(flagSet, &fs.Config.ClientKey, "client-key", "", fs.Config.ClientKey, "Client SSL private key (PEM) for mutual TLS auth")
+	flags.FVarP(flagSet, &fs.Config.MultiThreadCutoff, "multi-thread-cutoff", "", "Use multi-thread downloads for files above this size.")
+	flags.IntVarP(flagSet, &fs.Config.MultiThreadStreams, "multi-thread-streams", "", fs.Config.MultiThreadStreams, "Max number of streams to use for multi-thread downloads.")
 }
 
 // SetFlags converts any flags into config which weren't straight forward

fs/operations/multithread.go

@@ -0,0 +1,171 @@
+package operations
+
+import (
+	"context"
+	"io"
+
+	"github.com/ncw/rclone/fs"
+	"github.com/ncw/rclone/fs/accounting"
+	"github.com/pkg/errors"
+	"golang.org/x/sync/errgroup"
+)
+
+const (
+	multithreadChunkSize     = 64 << 10
+	multithreadChunkSizeMask = multithreadChunkSize - 1
+	multithreadBufferSize    = 32 * 1024
+)
+
+// state for a multi-thread copy
+type multiThreadCopyState struct {
+	ctx      context.Context
+	partSize int64
+	size     int64
+	wc       fs.WriterAtCloser
+	src      fs.Object
+	acc      *accounting.Account
+	streams  int
+}
+
+// Copy a single stream into place
+func (mc *multiThreadCopyState) copyStream(stream int) (err error) {
+	defer func() {
+		if err != nil {
+			fs.Debugf(mc.src, "multi-thread copy: stream %d/%d failed: %v", stream+1, mc.streams, err)
+		}
+	}()
+	start := int64(stream) * mc.partSize
+	if start >= mc.size {
+		return nil
+	}
+	end := start + mc.partSize
+	if end > mc.size {
+		end = mc.size
+	}
+
+	fs.Debugf(mc.src, "multi-thread copy: stream %d/%d (%d-%d) size %v starting", stream+1, mc.streams, start, end, fs.SizeSuffix(end-start))
+
+	rc, err := newReOpen(mc.src, nil, &fs.RangeOption{Start: start, End: end - 1}, fs.Config.LowLevelRetries)
+	if err != nil {
+		return errors.Wrap(err, "multpart copy: failed to open source")
+	}
+	defer fs.CheckClose(rc, &err)
+
+	// Copy the data
+	buf := make([]byte, multithreadBufferSize)
+	offset := start
+	for {
+		// Check if context cancelled and exit if so
+		if mc.ctx.Err() != nil {
+			return mc.ctx.Err()
+		}
+		nr, er := rc.Read(buf)
+		if nr > 0 {
+			err = mc.acc.AccountRead(nr)
+			if err != nil {
+				return errors.Wrap(err, "multpart copy: accounting failed")
+			}
+			nw, ew := mc.wc.WriteAt(buf[0:nr], offset)
+			if nw > 0 {
+				offset += int64(nw)
+			}
+			if ew != nil {
+				return errors.Wrap(ew, "multpart copy: write failed")
+			}
+			if nr != nw {
+				return errors.Wrap(io.ErrShortWrite, "multpart copy")
+			}
+		}
+		if er != nil {
+			if er != io.EOF {
+				return errors.Wrap(er, "multpart copy: read failed")
+			}
+			break
+		}
+	}
+
+	if offset != end {
+		return errors.Errorf("multpart copy: wrote %d bytes but expected to write %d", offset-start, end-start)
+	}
+
+	fs.Debugf(mc.src, "multi-thread copy: stream %d/%d (%d-%d) size %v finished", stream+1, mc.streams, start, end, fs.SizeSuffix(end-start))
+	return nil
+}
+
+// Calculate the chunk sizes and updated number of streams
+func (mc *multiThreadCopyState) calculateChunks() {
+	partSize := mc.size / int64(mc.streams)
+	// Round partition size up so partSize * streams >= size
+	if (mc.size % int64(mc.streams)) != 0 {
+		partSize++
+	}
+	// round partSize up to nearest multithreadChunkSize boundary
+	mc.partSize = (partSize + multithreadChunkSizeMask) &^ multithreadChunkSizeMask
+	// recalculate number of streams
+	mc.streams = int(mc.size / mc.partSize)
+	// round streams up so partSize * streams >= size
+	if (mc.size % mc.partSize) != 0 {
+		mc.streams++
+	}
+}
+
+// Copy src to (f, remote) using streams download threads and the OpenWriterAt feature
+func multiThreadCopy(f fs.Fs, remote string, src fs.Object, streams int) (newDst fs.Object, err error) {
+	openWriterAt := f.Features().OpenWriterAt
+	if openWriterAt == nil {
+		return nil, errors.New("multi-thread copy: OpenWriterAt not supported")
+	}
+	if src.Size() < 0 {
+		return nil, errors.New("multi-thread copy: can't copy unknown sized file")
+	}
+	if src.Size() == 0 {
+		return nil, errors.New("multi-thread copy: can't copy zero sized file")
+	}
+
+	g, ctx := errgroup.WithContext(context.Background())
+	mc := &multiThreadCopyState{
+		ctx:     ctx,
+		size:    src.Size(),
+		src:     src,
+		streams: streams,
+	}
+	mc.calculateChunks()
+
+	// Make accounting
+	mc.acc = accounting.NewAccount(nil, src)
+	defer fs.CheckClose(mc.acc, &err)
+
+	// create write file handle
+	mc.wc, err = openWriterAt(remote, mc.size)
+	if err != nil {
+		return nil, errors.Wrap(err, "multpart copy: failed to open destination")
+	}
+	defer fs.CheckClose(mc.wc, &err)
+
+	fs.Debugf(src, "Starting multi-thread copy with %d parts of size %v", mc.streams, fs.SizeSuffix(mc.partSize))
+	for stream := 0; stream < mc.streams; stream++ {
+		stream := stream
+		g.Go(func() (err error) {
+			return mc.copyStream(stream)
+		})
+	}
+	err = g.Wait()
+	if err != nil {
+		return nil, err
+	}
+
+	obj, err := f.NewObject(remote)
+	if err != nil {
+		return nil, errors.Wrap(err, "multi-thread copy: failed to find object after copy")
+	}
+
+	err = obj.SetModTime(src.ModTime())
+	switch err {
+	case nil, fs.ErrorCantSetModTime, fs.ErrorCantSetModTimeWithoutDelete:
+	default:
+		return nil, errors.Wrap(err, "multi-thread copy: failed to set modification time")
+	}
+
+	fs.Debugf(src, "Finished multi-thread copy with %d parts of size %v", mc.streams, fs.SizeSuffix(mc.partSize))
+	return obj, nil
+}

fs/operations/multithread_test.go

@@ -0,0 +1,70 @@
+package operations
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/ncw/rclone/fs"
+	"github.com/ncw/rclone/fstest"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMultithreadCalculateChunks(t *testing.T) {
+	for _, test := range []struct {
+		size         int64
+		streams      int
+		wantPartSize int64
+		wantStreams  int
+	}{
+		{size: 1, streams: 10, wantPartSize: multithreadChunkSize, wantStreams: 1},
+		{size: 1 << 20, streams: 1, wantPartSize: 1 << 20, wantStreams: 1},
+		{size: 1 << 20, streams: 2, wantPartSize: 1 << 19, wantStreams: 2},
+		{size: (1 << 20) + 1, streams: 2, wantPartSize: (1 << 19) + multithreadChunkSize, wantStreams: 2},
+		{size: (1 << 20) - 1, streams: 2, wantPartSize: (1 << 19), wantStreams: 2},
+	} {
+		t.Run(fmt.Sprintf("%+v", test), func(t *testing.T) {
+			mc := &multiThreadCopyState{
+				size:    test.size,
+				streams: test.streams,
+			}
+			mc.calculateChunks()
+			assert.Equal(t, test.wantPartSize, mc.partSize)
+			assert.Equal(t, test.wantStreams, mc.streams)
+		})
+	}
+}
+
+func TestMultithreadCopy(t *testing.T) {
+	r := fstest.NewRun(t)
+	defer r.Finalise()
+
+	for _, test := range []struct {
+		size    int
+		streams int
+	}{
+		{size: multithreadChunkSize*2 - 1, streams: 2},
+		{size: multithreadChunkSize * 2, streams: 2},
+		{size: multithreadChunkSize*2 + 1, streams: 2},
+	} {
+		t.Run(fmt.Sprintf("%+v", test), func(t *testing.T) {
+			contents := fstest.RandomString(test.size)
+			t1 := fstest.Time("2001-02-03T04:05:06.499999999Z")
+			file1 := r.WriteObject("file1", contents, t1)
+			fstest.CheckItems(t, r.Fremote, file1)
+			fstest.CheckItems(t, r.Flocal)
+
+			src, err := r.Fremote.NewObject("file1")
+			require.NoError(t, err)
+
+			dst, err := multiThreadCopy(r.Flocal, "file1", src, 2)
+			require.NoError(t, err)
+			assert.Equal(t, src.Size(), dst.Size())
+			assert.Equal(t, "file1", dst.Remote())
+
+			fstest.CheckListingWithPrecision(t, r.Fremote, []fstest.Item{file1}, nil, fs.ModTimeNotSupported)
+			require.NoError(t, dst.Remove())
+		})
+	}
+
+}

fs/operations/operations.go

@@ -292,6 +292,23 @@ func Copy(f fs.Fs, dst fs.Object, remote string, src fs.Object) (newDst fs.Objec
 		}
 		// If can't server side copy, do it manually
 		if err == fs.ErrorCantCopy {
+			if doOpenWriterAt := f.Features().OpenWriterAt; doOpenWriterAt != nil && src.Size() >= int64(fs.Config.MultiThreadCutoff) && fs.Config.MultiThreadStreams > 1 {
+				// Number of streams proportional to size
+				streams := src.Size() / int64(fs.Config.MultiThreadCutoff)
+				// With maximum
+				if streams > int64(fs.Config.MultiThreadStreams) {
+					streams = int64(fs.Config.MultiThreadStreams)
+				}
+				if streams < 2 {
+					streams = 2
+				}
+				dst, err = multiThreadCopy(f, remote, src, int(streams))
+				if doUpdate {
+					actionTaken = "Multi-thread Copied (replaced existing)"
+				} else {
+					actionTaken = "Multi-thread Copied (new)"
+				}
+			} else {
 				var in0 io.ReadCloser
 				in0, err = newReOpen(src, hashOption, nil, fs.Config.LowLevelRetries)
 				if err != nil {
@@ -328,6 +345,7 @@ func Copy(f fs.Fs, dst fs.Object, remote string, src fs.Object) (newDst fs.Objec
 					}
 				}
 			}
+		}
 		tries++
 		if tries >= maxTries {
 			break