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// Copyright 2016 The Netstack Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package queue provides the implementation of buffer queue
// and interface of queue entry with Length method.
package queue
import (
"sync"
"gvisor.googlesource.com/gvisor/pkg/ilist"
"gvisor.googlesource.com/gvisor/pkg/tcpip"
"gvisor.googlesource.com/gvisor/pkg/waiter"
)
// Entry implements Linker interface and has both Length and Release methods.
type Entry interface {
ilist.Linker
Length() int64
Release()
Peek() Entry
}
// Queue is a buffer queue.
type Queue struct {
ReaderQueue *waiter.Queue
WriterQueue *waiter.Queue
mu sync.Mutex `state:"nosave"`
closed bool
used int64
limit int64
dataList ilist.List
}
// New allocates and initializes a new queue.
func New(ReaderQueue *waiter.Queue, WriterQueue *waiter.Queue, limit int64) *Queue {
return &Queue{ReaderQueue: ReaderQueue, WriterQueue: WriterQueue, limit: limit}
}
// Close closes q for reading and writing. It is immediately not writable and
// will become unreadble will no more data is pending.
//
// Both the read and write queues must be notified after closing:
// q.ReaderQueue.Notify(waiter.EventIn)
// q.WriterQueue.Notify(waiter.EventOut)
func (q *Queue) Close() {
q.mu.Lock()
q.closed = true
q.mu.Unlock()
}
// Reset empties the queue and Releases all of the Entries.
//
// Both the read and write queues must be notified after resetting:
// q.ReaderQueue.Notify(waiter.EventIn)
// q.WriterQueue.Notify(waiter.EventOut)
func (q *Queue) Reset() {
q.mu.Lock()
for cur := q.dataList.Front(); cur != nil; cur = cur.Next() {
cur.(Entry).Release()
}
q.dataList.Reset()
q.used = 0
q.mu.Unlock()
}
// IsReadable determines if q is currently readable.
func (q *Queue) IsReadable() bool {
q.mu.Lock()
defer q.mu.Unlock()
return q.closed || q.dataList.Front() != nil
}
// IsWritable determines if q is currently writable.
func (q *Queue) IsWritable() bool {
q.mu.Lock()
defer q.mu.Unlock()
return q.closed || q.used < q.limit
}
// Enqueue adds an entry to the data queue if room is available.
//
// If notify is true, ReaderQueue.Notify must be called:
// q.ReaderQueue.Notify(waiter.EventIn)
func (q *Queue) Enqueue(e Entry) (notify bool, err *tcpip.Error) {
q.mu.Lock()
if q.closed {
q.mu.Unlock()
return false, tcpip.ErrClosedForSend
}
if q.used >= q.limit {
q.mu.Unlock()
return false, tcpip.ErrWouldBlock
}
notify = q.dataList.Front() == nil
q.used += e.Length()
q.dataList.PushBack(e)
q.mu.Unlock()
return notify, nil
}
// Dequeue removes the first entry in the data queue, if one exists.
//
// If notify is true, WriterQueue.Notify must be called:
// q.WriterQueue.Notify(waiter.EventOut)
func (q *Queue) Dequeue() (e Entry, notify bool, err *tcpip.Error) {
q.mu.Lock()
if q.dataList.Front() == nil {
err := tcpip.ErrWouldBlock
if q.closed {
err = tcpip.ErrClosedForReceive
}
q.mu.Unlock()
return nil, false, err
}
notify = q.used >= q.limit
e = q.dataList.Front().(Entry)
q.dataList.Remove(e)
q.used -= e.Length()
notify = notify && q.used < q.limit
q.mu.Unlock()
return e, notify, nil
}
// Peek returns the first entry in the data queue, if one exists.
func (q *Queue) Peek() (Entry, *tcpip.Error) {
q.mu.Lock()
defer q.mu.Unlock()
if q.dataList.Front() == nil {
err := tcpip.ErrWouldBlock
if q.closed {
err = tcpip.ErrClosedForReceive
}
return nil, err
}
return q.dataList.Front().(Entry).Peek(), nil
}
// QueuedSize returns the number of bytes currently in the queue, that is, the
// number of readable bytes.
func (q *Queue) QueuedSize() int64 {
return q.used
}
// MaxQueueSize returns the maximum number of bytes storable in the queue.
func (q *Queue) MaxQueueSize() int64 {
return q.limit
}
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