accounting: refactor bwlimit code to allow for multiple slots

fs/accounting/accounting.go

@@ -10,7 +10,6 @@ import (
 	"unicode/utf8"
 
 	"github.com/rclone/rclone/fs/rc"
-	"golang.org/x/time/rate"
 
 	"github.com/pkg/errors"
 	"github.com/rclone/rclone/fs"
@@ -50,7 +49,7 @@ type Account struct {
 	exit    chan struct{} // channel that will be closed when transfer is finished
 	withBuf bool          // is using a buffered in
 
-	tokenBucket *rate.Limiter // per file bandwidth limiter (may be nil)
+	tokenBucket buckets // per file bandwidth limiter (may be nil)
 
 	values accountValues
 }
@@ -289,7 +288,7 @@ func (acc *Account) DryRun(n int64) {
 // Account for n bytes from the current file bandwidth limit (if any)
 func (acc *Account) limitPerFileBandwidth(n int) {
 	acc.values.mu.Lock()
-	tokenBucket := acc.tokenBucket
+	tokenBucket := acc.tokenBucket[TokenBucketSlotAccounting]
 	acc.values.mu.Unlock()
 
 	if tokenBucket != nil {
@@ -310,7 +309,7 @@ func (acc *Account) accountRead(n int) {
 
 	acc.stats.Bytes(int64(n))
 
-	limitBandwidth(n)
+	TokenBucket.LimitBandwidth(TokenBucketSlotAccounting, n)
 	acc.limitPerFileBandwidth(n)
 }