Update dependencies

vendor/gvisor.dev/gvisor/pkg/waiter/waiter.go

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+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package waiter provides the implementation of a wait queue, where waiters can
+// be enqueued to be notified when an event of interest happens.
+//
+// Becoming readable and/or writable are examples of events. Waiters are
+// expected to use a pattern similar to this to make a blocking function out of
+// a non-blocking one:
+//
+//	func (o *object) blockingRead(...) error {
+//		err := o.nonBlockingRead(...)
+//		if err != ErrAgain {
+//			// Completed with no need to wait!
+//			return err
+//		}
+//
+//		e := createOrGetWaiterEntry(...)
+//		o.EventRegister(&e, waiter.EventIn)
+//		defer o.EventUnregister(&e)
+//
+//		// We need to try to read again after registration because the
+//		// object may have become readable between the last attempt to
+//		// read and read registration.
+//		err = o.nonBlockingRead(...)
+//		for err == ErrAgain {
+//			wait()
+//			err = o.nonBlockingRead(...)
+//		}
+//
+//		return err
+//	}
+//
+// Another goroutine needs to notify waiters when events happen. For example:
+//
+//	func (o *object) Write(...) ... {
+//		// Do write work.
+//		[...]
+//
+//		if oldDataAvailableSize == 0 && dataAvailableSize > 0 {
+//			// If no data was available and now some data is
+//			// available, the object became readable, so notify
+//			// potential waiters about this.
+//			o.Notify(waiter.EventIn)
+//		}
+//	}
+package waiter
+
+import (
+	"gvisor.dev/gvisor/pkg/sync"
+)
+
+// EventMask represents io events as used in the poll() syscall.
+type EventMask uint64
+
+// Events that waiters can wait on. The meaning is the same as those in the
+// poll() syscall.
+const (
+	EventIn       EventMask = 0x01   // POLLIN
+	EventPri      EventMask = 0x02   // POLLPRI
+	EventOut      EventMask = 0x04   // POLLOUT
+	EventErr      EventMask = 0x08   // POLLERR
+	EventHUp      EventMask = 0x10   // POLLHUP
+	EventRdNorm   EventMask = 0x0040 // POLLRDNORM
+	EventWrNorm   EventMask = 0x0100 // POLLWRNORM
+	EventInternal EventMask = 0x1000
+	EventRdHUp    EventMask = 0x2000 // POLLRDHUP
+
+	allEvents      EventMask = 0x1f | EventRdNorm | EventWrNorm | EventRdHUp
+	ReadableEvents EventMask = EventIn | EventRdNorm
+	WritableEvents EventMask = EventOut | EventWrNorm
+)
+
+// EventMaskFromLinux returns an EventMask representing the supported events
+// from the Linux events e, which is in the format used by poll(2).
+func EventMaskFromLinux(e uint32) EventMask {
+	// Our flag definitions are currently identical to Linux.
+	return EventMask(e) & allEvents
+}
+
+// ToLinux returns e in the format used by Linux poll(2).
+func (e EventMask) ToLinux() uint32 {
+	// Our flag definitions are currently identical to Linux.
+	return uint32(e)
+}
+
+// Waitable contains the methods that need to be implemented by waitable
+// objects.
+type Waitable interface {
+	// Readiness returns what the object is currently ready for. If it's
+	// not ready for a desired purpose, the caller may use EventRegister and
+	// EventUnregister to get notifications once the object becomes ready.
+	//
+	// Implementations should allow for events like EventHUp and EventErr
+	// to be returned regardless of whether they are in the input EventMask.
+	Readiness(mask EventMask) EventMask
+
+	// EventRegister registers the given waiter entry to receive
+	// notifications when an event occurs that makes the object ready for
+	// at least one of the events in mask.
+	EventRegister(e *Entry) error
+
+	// EventUnregister unregisters a waiter entry previously registered with
+	// EventRegister().
+	EventUnregister(e *Entry)
+}
+
+// EventListener provides a notify callback.
+type EventListener interface {
+	// NotifyEvent is the function to be called when the waiter entry is
+	// notified. It is responsible for doing whatever is needed to wake up
+	// the waiter.
+	//
+	// The callback is supposed to perform minimal work, and cannot call
+	// any method on the queue itself because it will be locked while the
+	// callback is running.
+	//
+	// The mask indicates the events that occurred and that the entry is
+	// interested in.
+	NotifyEvent(mask EventMask)
+}
+
+// Entry represents a waiter that can be add to the a wait queue. It can
+// only be in one queue at a time, and is added "intrusively" to the queue with
+// no extra memory allocations.
+//
+// +stateify savable
+type Entry struct {
+	waiterEntry
+
+	// eventListener receives the notification.
+	eventListener EventListener
+
+	// mask should be immutable once queued.
+	mask EventMask
+}
+
+// Init initializes the Entry.
+//
+// This must only be called when unregistered.
+func (e *Entry) Init(eventListener EventListener, mask EventMask) {
+	e.eventListener = eventListener
+	e.mask = mask
+}
+
+// Mask returns the entry mask.
+func (e *Entry) Mask() EventMask {
+	return e.mask
+}
+
+// NotifyEvent notifies the event listener.
+//
+// Mask should be the full set of active events.
+func (e *Entry) NotifyEvent(mask EventMask) {
+	if m := mask & e.mask; m != 0 {
+		e.eventListener.NotifyEvent(m)
+	}
+}
+
+// ChannelNotifier is a simple channel-based notification.
+type ChannelNotifier chan struct{}
+
+// NotifyEvent implements waiter.EventListener.NotifyEvent.
+func (c ChannelNotifier) NotifyEvent(EventMask) {
+	select {
+	case c <- struct{}{}:
+	default:
+	}
+}
+
+// NewChannelEntry initializes a new Entry that does a non-blocking write to a
+// struct{} channel when the callback is called. It returns the new Entry
+// instance and the channel being used.
+func NewChannelEntry(mask EventMask) (e Entry, ch chan struct{}) {
+	ch = make(chan struct{}, 1)
+	e.Init(ChannelNotifier(ch), mask)
+	return e, ch
+}
+
+type functionNotifier func(EventMask)
+
+// NotifyEvent implements waiter.EventListener.NotifyEvent.
+func (f functionNotifier) NotifyEvent(mask EventMask) {
+	f(mask)
+}
+
+// NewFunctionEntry initializes a new Entry that calls the given function.
+func NewFunctionEntry(mask EventMask, fn func(EventMask)) (e Entry) {
+	e.Init(functionNotifier(fn), mask)
+	return e
+}
+
+// Queue represents the wait queue where waiters can be added and
+// notifiers can notify them when events happen.
+//
+// The zero value for waiter.Queue is an empty queue ready for use.
+//
+// +stateify savable
+type Queue struct {
+	list waiterList
+	mu   sync.RWMutex `state:"nosave"`
+}
+
+// EventRegister adds a waiter to the wait queue.
+func (q *Queue) EventRegister(e *Entry) {
+	q.mu.Lock()
+	q.list.PushBack(e)
+	q.mu.Unlock()
+}
+
+// EventUnregister removes the given waiter entry from the wait queue.
+func (q *Queue) EventUnregister(e *Entry) {
+	q.mu.Lock()
+	q.list.Remove(e)
+	q.mu.Unlock()
+}
+
+// Notify notifies all waiters in the queue whose masks have at least one bit
+// in common with the notification mask.
+func (q *Queue) Notify(mask EventMask) {
+	q.mu.RLock()
+	for e := q.list.Front(); e != nil; e = e.Next() {
+		m := mask & e.mask
+		if m == 0 {
+			continue
+		}
+		e.eventListener.NotifyEvent(m) // Skip intermediate call.
+	}
+	q.mu.RUnlock()
+}
+
+// Events returns the set of events being waited on. It is the union of the
+// masks of all registered entries.
+func (q *Queue) Events() EventMask {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+	ret := EventMask(0)
+	for e := q.list.Front(); e != nil; e = e.Next() {
+		ret |= e.mask
+	}
+	return ret
+}
+
+// IsEmpty returns if the wait queue is empty or not.
+func (q *Queue) IsEmpty() bool {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+	return q.list.Front() == nil
+}
+
+// AlwaysReady implements the Waitable interface but is always ready. Embedding
+// this struct into another struct makes it implement the boilerplate empty
+// functions automatically.
+type AlwaysReady struct {
+}
+
+// Readiness always returns the input mask because this object is always ready.
+func (*AlwaysReady) Readiness(mask EventMask) EventMask {
+	return mask
+}
+
+// EventRegister doesn't do anything because this object doesn't need to issue
+// notifications because its readiness never changes.
+func (*AlwaysReady) EventRegister(*Entry) error {
+	return nil
+}
+
+// EventUnregister doesn't do anything because this object doesn't need to issue
+// notifications because its readiness never changes.
+func (*AlwaysReady) EventUnregister(e *Entry) {
+}
+
+// NeverReady implements the Waitable interface but is never ready. Otherwise,
+// this is exactly the same as AlwaysReady.
+type NeverReady struct {
+}
+
+// Readiness always returns the input mask because this object is always ready.
+func (*NeverReady) Readiness(mask EventMask) EventMask {
+	return mask
+}
+
+// EventRegister doesn't do anything because this object doesn't need to issue
+// notifications because its readiness never changes.
+func (*NeverReady) EventRegister(e *Entry) error {
+	return nil
+}
+
+// EventUnregister doesn't do anything because this object doesn't need to issue
+// notifications because its readiness never changes.
+func (*NeverReady) EventUnregister(e *Entry) {
+}