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moby--moby/distribution/xfer/transfer.go

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package xfer // import "github.com/docker/docker/distribution/xfer"
import (
"context"
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
"runtime"
"sync"
"github.com/docker/docker/pkg/progress"
)
// DoNotRetry is an error wrapper indicating that the error cannot be resolved
// with a retry.
type DoNotRetry struct {
Err error
}
// Error returns the stringified representation of the encapsulated error.
func (e DoNotRetry) Error() string {
return e.Err.Error()
}
// Watcher is returned by Watch and can be passed to Release to stop watching.
type Watcher struct {
// signalChan is used to signal to the watcher goroutine that
// new progress information is available, or that the transfer
// has finished.
signalChan chan struct{}
// releaseChan signals to the watcher goroutine that the watcher
// should be detached.
releaseChan chan struct{}
// running remains open as long as the watcher is watching the
// transfer. It gets closed if the transfer finishes or the
// watcher is detached.
running chan struct{}
}
// Transfer represents an in-progress transfer.
type Transfer interface {
Watch(progressOutput progress.Output) *Watcher
Release(*Watcher)
Context() context.Context
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
Close()
Done() <-chan struct{}
Released() <-chan struct{}
Broadcast(masterProgressChan <-chan progress.Progress)
}
type transfer struct {
mu sync.Mutex
ctx context.Context
cancel context.CancelFunc
// watchers keeps track of the goroutines monitoring progress output,
// indexed by the channels that release them.
watchers map[chan struct{}]*Watcher
// lastProgress is the most recently received progress event.
lastProgress progress.Progress
// hasLastProgress is true when lastProgress has been set.
hasLastProgress bool
// running remains open as long as the transfer is in progress.
running chan struct{}
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
// released stays open until all watchers release the transfer and
// the transfer is no longer tracked by the transfer manager.
released chan struct{}
// broadcastDone is true if the master progress channel has closed.
broadcastDone bool
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
// closed is true if Close has been called
closed bool
// broadcastSyncChan allows watchers to "ping" the broadcasting
// goroutine to wait for it for deplete its input channel. This ensures
// a detaching watcher won't miss an event that was sent before it
// started detaching.
broadcastSyncChan chan struct{}
}
// NewTransfer creates a new transfer.
func NewTransfer() Transfer {
t := &transfer{
watchers: make(map[chan struct{}]*Watcher),
running: make(chan struct{}),
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
released: make(chan struct{}),
broadcastSyncChan: make(chan struct{}),
}
// This uses context.Background instead of a caller-supplied context
// so that a transfer won't be cancelled automatically if the client
// which requested it is ^C'd (there could be other viewers).
t.ctx, t.cancel = context.WithCancel(context.Background())
return t
}
// Broadcast copies the progress and error output to all viewers.
func (t *transfer) Broadcast(masterProgressChan <-chan progress.Progress) {
for {
var (
p progress.Progress
ok bool
)
select {
case p, ok = <-masterProgressChan:
default:
// We've depleted the channel, so now we can handle
// reads on broadcastSyncChan to let detaching watchers
// know we're caught up.
select {
case <-t.broadcastSyncChan:
continue
case p, ok = <-masterProgressChan:
}
}
t.mu.Lock()
if ok {
t.lastProgress = p
t.hasLastProgress = true
for _, w := range t.watchers {
select {
case w.signalChan <- struct{}{}:
default:
}
}
} else {
t.broadcastDone = true
}
t.mu.Unlock()
if !ok {
close(t.running)
return
}
}
}
// Watch adds a watcher to the transfer. The supplied channel gets progress
// updates and is closed when the transfer finishes.
func (t *transfer) Watch(progressOutput progress.Output) *Watcher {
t.mu.Lock()
defer t.mu.Unlock()
w := &Watcher{
releaseChan: make(chan struct{}),
signalChan: make(chan struct{}),
running: make(chan struct{}),
}
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
t.watchers[w.releaseChan] = w
if t.broadcastDone {
close(w.running)
return w
}
go func() {
defer func() {
close(w.running)
}()
var (
done bool
lastWritten progress.Progress
hasLastWritten bool
)
for {
t.mu.Lock()
hasLastProgress := t.hasLastProgress
lastProgress := t.lastProgress
t.mu.Unlock()
// Make sure we don't write the last progress item
// twice.
if hasLastProgress && (!done || !hasLastWritten || lastProgress != lastWritten) {
progressOutput.WriteProgress(lastProgress)
lastWritten = lastProgress
hasLastWritten = true
}
if done {
return
}
select {
case <-w.signalChan:
case <-w.releaseChan:
done = true
// Since the watcher is going to detach, make
// sure the broadcaster is caught up so we
// don't miss anything.
select {
case t.broadcastSyncChan <- struct{}{}:
case <-t.running:
}
case <-t.running:
done = true
}
}
}()
return w
}
// Release is the inverse of Watch; indicating that the watcher no longer wants
// to be notified about the progress of the transfer. All calls to Watch must
// be paired with later calls to Release so that the lifecycle of the transfer
// is properly managed.
func (t *transfer) Release(watcher *Watcher) {
t.mu.Lock()
delete(t.watchers, watcher.releaseChan)
if len(t.watchers) == 0 {
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
if t.closed {
// released may have been closed already if all
// watchers were released, then another one was added
// while waiting for a previous watcher goroutine to
// finish.
select {
case <-t.released:
default:
close(t.released)
}
} else {
t.cancel()
}
}
t.mu.Unlock()
close(watcher.releaseChan)
// Block until the watcher goroutine completes
<-watcher.running
}
// Done returns a channel which is closed if the transfer completes or is
// cancelled. Note that having 0 watchers causes a transfer to be cancelled.
func (t *transfer) Done() <-chan struct{} {
// Note that this doesn't return t.ctx.Done() because that channel will
// be closed the moment Cancel is called, and we need to return a
// channel that blocks until a cancellation is actually acknowledged by
// the transfer function.
return t.running
}
// Released returns a channel which is closed once all watchers release the
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
// transfer AND the transfer is no longer tracked by the transfer manager.
func (t *transfer) Released() <-chan struct{} {
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
return t.released
}
// Context returns the context associated with the transfer.
func (t *transfer) Context() context.Context {
return t.ctx
}
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
// Close is called by the transfer manager when the transfer is no longer
// being tracked.
func (t *transfer) Close() {
t.mu.Lock()
t.closed = true
if len(t.watchers) == 0 {
close(t.released)
}
t.mu.Unlock()
}
// DoFunc is a function called by the transfer manager to actually perform
// a transfer. It should be non-blocking. It should wait until the start channel
// is closed before transferring any data. If the function closes inactive, that
// signals to the transfer manager that the job is no longer actively moving
// data - for example, it may be waiting for a dependent transfer to finish.
// This prevents it from taking up a slot.
type DoFunc func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) Transfer
// TransferManager is used by LayerDownloadManager and LayerUploadManager to
// schedule and deduplicate transfers. It is up to the TransferManager
// implementation to make the scheduling and concurrency decisions.
type TransferManager interface {
// Transfer checks if a transfer with the given key is in progress. If
// so, it returns progress and error output from that transfer.
// Otherwise, it will call xferFunc to initiate the transfer.
Transfer(key string, xferFunc DoFunc, progressOutput progress.Output) (Transfer, *Watcher)
// SetConcurrency set the concurrencyLimit so that it is adjustable daemon reload
SetConcurrency(concurrency int)
}
type transferManager struct {
mu sync.Mutex
concurrencyLimit int
activeTransfers int
transfers map[string]Transfer
waitingTransfers []chan struct{}
}
// NewTransferManager returns a new TransferManager.
func NewTransferManager(concurrencyLimit int) TransferManager {
return &transferManager{
concurrencyLimit: concurrencyLimit,
transfers: make(map[string]Transfer),
}
}
// SetConcurrency sets the concurrencyLimit
func (tm *transferManager) SetConcurrency(concurrency int) {
tm.mu.Lock()
tm.concurrencyLimit = concurrency
tm.mu.Unlock()
}
// Transfer checks if a transfer matching the given key is in progress. If not,
// it starts one by calling xferFunc. The caller supplies a channel which
// receives progress output from the transfer.
func (tm *transferManager) Transfer(key string, xferFunc DoFunc, progressOutput progress.Output) (Transfer, *Watcher) {
tm.mu.Lock()
defer tm.mu.Unlock()
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
for {
xfer, present := tm.transfers[key]
if !present {
break
}
// Transfer is already in progress.
watcher := xfer.Watch(progressOutput)
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
select {
case <-xfer.Context().Done():
// We don't want to watch a transfer that has been cancelled.
// Wait for it to be removed from the map and try again.
xfer.Release(watcher)
tm.mu.Unlock()
// The goroutine that removes this transfer from the
// map is also waiting for xfer.Done(), so yield to it.
// This could be avoided by adding a Closed method
// to Transfer to allow explicitly waiting for it to be
// removed the map, but forcing a scheduling round in
// this very rare case seems better than bloating the
// interface definition.
runtime.Gosched()
<-xfer.Done()
tm.mu.Lock()
default:
return xfer, watcher
}
}
start := make(chan struct{})
inactive := make(chan struct{})
if tm.concurrencyLimit == 0 || tm.activeTransfers < tm.concurrencyLimit {
close(start)
tm.activeTransfers++
} else {
tm.waitingTransfers = append(tm.waitingTransfers, start)
}
masterProgressChan := make(chan progress.Progress)
xfer := xferFunc(masterProgressChan, start, inactive)
watcher := xfer.Watch(progressOutput)
go xfer.Broadcast(masterProgressChan)
tm.transfers[key] = xfer
// When the transfer is finished, remove from the map.
go func() {
for {
select {
case <-inactive:
tm.mu.Lock()
tm.inactivate(start)
tm.mu.Unlock()
inactive = nil
case <-xfer.Done():
tm.mu.Lock()
if inactive != nil {
tm.inactivate(start)
}
delete(tm.transfers, key)
tm.mu.Unlock()
Fix watching a released transfer Things could go wrong if Watch was called after the last existing watcher was released. The call to Watch would succeed even though it was not really adding a watcher, and the corresponding call to Release would close hasWatchers a second time. The fix for this is twofold: 1. We allow transfers to gain new watchers after the watcher count has touched zero. This means that the channel returned by Released should not be closed until all watchers have been released AND the transfer is no longer tracked by the transfer manager, meaning it won't be possible for additional calls to Watch to race with closing the channel returned by Released. The Transfer interface has a new method called Close so the transfer can know when the transfer manager no longer references it. Remove the Cancel method. It's not used and should not be exported. 2. Even though (1) makes it possible to add watchers after all the previous watchers have been released, we want to avoid doing this in practice. A transfer that has had all its watchers released is in the process of being cancelled, and attaching to one of these will never be the correct behavior. Add a check if a watcher is attaching to a cancelled transfer. In this case, wait for the transfer to be removed from the map and try again. This will ensure correct behavior when a watcher tries to attach during the race window. Either (1) or (2) should be sufficient to fix the race involved here, but the combination is the most correct approach. (1) fixes the low-level plumbing to be resilient to the race condition, and (2) avoids using it in a racy way. Fixes #19606 Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2016-01-25 14:37:09 -05:00
xfer.Close()
return
}
}
}()
return xfer, watcher
}
func (tm *transferManager) inactivate(start chan struct{}) {
// If the transfer was started, remove it from the activeTransfers
// count.
select {
case <-start:
// Start next transfer if any are waiting
if len(tm.waitingTransfers) != 0 {
close(tm.waitingTransfers[0])
tm.waitingTransfers = tm.waitingTransfers[1:]
} else {
tm.activeTransfers--
}
default:
}
}