rclone/fs/accounting/transfermap.go
Nick Craig-Wood f5439ddc54 accounting: fix deadlock in stats printing
The deadlock was caused in transfermap.go by calling mu.RLock() in one
function then calling it again in a sub function. Normally this is
fine, however this leaves a window where mu.Lock() can be called. When
mu.Lock() is called it doesn't allow the second mu.RLock() and
deadlocks.

    Thead 1                    Thread 2
    String():mu.RLock()
                               del():mu.Lock()
    sortedSlice():mu.RLock()                     - DEADLOCK

Lesson learnt: don't try using locks recursively ever!

This patch fixes the problem by removing the second mu.RLock(). This
was done by factoring the code that was calling it into the
transfermap.go file so all the locking can be seen at once which was
ultimately the cause of the problem - the code which used the locks
was too far away from the rest of the code using the lock.

This problem was introduced in:

bfa5715017 fs/accounting: sort transfers by start time

Which hasn't been released in a stable version yet
2020-08-05 17:13:00 +01:00

149 lines
3.3 KiB
Go

package accounting
import (
"fmt"
"sort"
"strings"
"sync"
"github.com/rclone/rclone/fs"
"github.com/rclone/rclone/fs/rc"
)
// transferMap holds name to transfer map
type transferMap struct {
mu sync.RWMutex
items map[string]*Transfer
name string
}
// newTransferMap creates a new empty transfer map of capacity size
func newTransferMap(size int, name string) *transferMap {
return &transferMap{
items: make(map[string]*Transfer, size),
name: name,
}
}
// add adds a new transfer to the map
func (tm *transferMap) add(tr *Transfer) {
tm.mu.Lock()
tm.items[tr.remote] = tr
tm.mu.Unlock()
}
// del removes a transfer from the map by name
func (tm *transferMap) del(remote string) {
tm.mu.Lock()
delete(tm.items, remote)
tm.mu.Unlock()
}
// merge adds items from another map
func (tm *transferMap) merge(m *transferMap) {
tm.mu.Lock()
m.mu.Lock()
for name, tr := range m.items {
tm.items[name] = tr
}
m.mu.Unlock()
tm.mu.Unlock()
}
// empty returns whether the map has any items
func (tm *transferMap) empty() bool {
tm.mu.RLock()
defer tm.mu.RUnlock()
return len(tm.items) == 0
}
// count returns the number of items in the map
func (tm *transferMap) count() int {
tm.mu.RLock()
defer tm.mu.RUnlock()
return len(tm.items)
}
// _sortedSlice returns all transfers sorted by start time
//
// Call with mu.Rlock held
func (tm *transferMap) _sortedSlice() []*Transfer {
s := make([]*Transfer, 0, len(tm.items))
for _, tr := range tm.items {
s = append(s, tr)
}
sort.Slice(s, func(i, j int) bool {
return s[i].startedAt.Before(s[j].startedAt)
})
return s
}
// String returns string representation of map items excluding any in
// exclude (if set).
func (tm *transferMap) String(progress *inProgress, exclude *transferMap) string {
tm.mu.RLock()
defer tm.mu.RUnlock()
strngs := make([]string, 0, len(tm.items))
for _, tr := range tm._sortedSlice() {
if exclude != nil {
exclude.mu.RLock()
_, found := exclude.items[tr.remote]
exclude.mu.RUnlock()
if found {
continue
}
}
var out string
if acc := progress.get(tr.remote); acc != nil {
out = acc.String()
} else {
out = fmt.Sprintf("%*s: %s",
fs.Config.StatsFileNameLength,
shortenName(tr.remote, fs.Config.StatsFileNameLength),
tm.name,
)
}
strngs = append(strngs, " * "+out)
}
return strings.Join(strngs, "\n")
}
// progress returns total bytes read as well as the size.
func (tm *transferMap) progress(stats *StatsInfo) (totalBytes, totalSize int64) {
tm.mu.RLock()
defer tm.mu.RUnlock()
for name := range tm.items {
if acc := stats.inProgress.get(name); acc != nil {
bytes, size := acc.progress()
if size >= 0 && bytes >= 0 {
totalBytes += bytes
totalSize += size
}
}
}
return totalBytes, totalSize
}
// remotes returns a []string of the remote names for the transferMap
func (tm *transferMap) remotes() (c []string) {
tm.mu.RLock()
defer tm.mu.RUnlock()
for _, tr := range tm._sortedSlice() {
c = append(c, tr.remote)
}
return c
}
// rcStats returns a []rc.Params of the stats for the transferMap
func (tm *transferMap) rcStats(progress *inProgress) (t []rc.Params) {
tm.mu.RLock()
defer tm.mu.RUnlock()
for _, tr := range tm._sortedSlice() {
if acc := progress.get(tr.remote); acc != nil {
t = append(t, acc.rcStats())
} else {
t = append(t, tr.rcStats())
}
}
return t
}