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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 transport
import (
"sync"
"gvisor.dev/gvisor/pkg/refs"
"gvisor.dev/gvisor/pkg/syserr"
"gvisor.dev/gvisor/pkg/waiter"
)
// queue is a buffer queue.
//
// +stateify savable
type queue struct {
refs.AtomicRefCount
ReaderQueue *waiter.Queue
WriterQueue *waiter.Queue
mu sync.Mutex `state:"nosave"`
closed bool
used int64
limit int64
dataList messageList
}
// Close closes q for reading and writing. It is immediately not writable and
// will become unreadable when 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.Release()
}
q.dataList.Reset()
q.used = 0
q.mu.Unlock()
}
// DecRef implements RefCounter.DecRef with destructor q.Reset.
func (q *queue) DecRef() {
q.DecRefWithDestructor(q.Reset)
// We don't need to notify after resetting because no one cares about
// this queue after all references have been dropped.
}
// 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
}
// bufWritable returns true if there is space for writing.
//
// N.B. Linux only considers a unix socket "writable" if >75% of the buffer is
// free.
//
// See net/unix/af_unix.c:unix_writeable.
func (q *queue) bufWritable() bool {
return 4*q.used < q.limit
}
// IsWritable determines if q is currently writable.
func (q *queue) IsWritable() bool {
q.mu.Lock()
defer q.mu.Unlock()
return q.closed || q.bufWritable()
}
// Enqueue adds an entry to the data queue if room is available.
//
// If truncate is true, Enqueue may truncate the message before enqueuing it.
// Otherwise, the entire message must fit. If n < e.Length(), err indicates why.
//
// If notify is true, ReaderQueue.Notify must be called:
// q.ReaderQueue.Notify(waiter.EventIn)
func (q *queue) Enqueue(e *message, truncate bool) (l int64, notify bool, err *syserr.Error) {
q.mu.Lock()
if q.closed {
q.mu.Unlock()
return 0, false, syserr.ErrClosedForSend
}
free := q.limit - q.used
l = e.Length()
if l > free && truncate {
if free == 0 {
// Message can't fit right now.
q.mu.Unlock()
return 0, false, syserr.ErrWouldBlock
}
e.Truncate(free)
l = e.Length()
err = syserr.ErrWouldBlock
}
if l > q.limit {
// Message is too big to ever fit.
q.mu.Unlock()
return 0, false, syserr.ErrMessageTooLong
}
if l > free {
// Message can't fit right now.
q.mu.Unlock()
return 0, false, syserr.ErrWouldBlock
}
notify = q.dataList.Front() == nil
q.used += l
q.dataList.PushBack(e)
q.mu.Unlock()
return l, notify, err
}
// 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 *message, notify bool, err *syserr.Error) {
q.mu.Lock()
if q.dataList.Front() == nil {
err := syserr.ErrWouldBlock
if q.closed {
err = syserr.ErrClosedForReceive
}
q.mu.Unlock()
return nil, false, err
}
notify = !q.bufWritable()
e = q.dataList.Front()
q.dataList.Remove(e)
q.used -= e.Length()
notify = notify && q.bufWritable()
q.mu.Unlock()
return e, notify, nil
}
// Peek returns the first entry in the data queue, if one exists.
func (q *queue) Peek() (*message, *syserr.Error) {
q.mu.Lock()
defer q.mu.Unlock()
if q.dataList.Front() == nil {
err := syserr.ErrWouldBlock
if q.closed {
err = syserr.ErrClosedForReceive
}
return nil, err
}
return q.dataList.Front().Peek(), nil
}
// QueuedSize returns the number of bytes currently in the queue, that is, the
// number of readable bytes.
func (q *queue) QueuedSize() int64 {
q.mu.Lock()
defer q.mu.Unlock()
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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