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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 tcp
import (
"sync"
"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
)
// segmentQueue is a bounded, thread-safe queue of TCP segments.
type segmentQueue struct {
mu sync.Mutex
list segmentList
limit int
used int
}
// empty determines if the queue is empty.
func (q *segmentQueue) empty() bool {
q.mu.Lock()
r := q.used == 0
q.mu.Unlock()
return r
}
// setLimit updates the limit. No segments are immediately dropped in case the
// queue becomes full due to the new limit.
func (q *segmentQueue) setLimit(limit int) {
q.mu.Lock()
q.limit = limit
q.mu.Unlock()
}
// enqueue adds the given segment to the queue.
//
// Returns true when the segment is successfully added to the queue, in which
// case ownership of the reference is transferred to the queue. And returns
// false if the queue is full, in which case ownership is retained by the
// caller.
func (q *segmentQueue) enqueue(s *segment) bool {
q.mu.Lock()
r := q.used < q.limit
if r {
q.list.PushBack(s)
q.used += s.data.Size() + header.TCPMinimumSize
}
q.mu.Unlock()
return r
}
// dequeue removes and returns the next segment from queue, if one exists.
// Ownership is transferred to the caller, who is responsible for decrementing
// the ref count when done.
func (q *segmentQueue) dequeue() *segment {
q.mu.Lock()
s := q.list.Front()
if s != nil {
q.list.Remove(s)
q.used -= s.data.Size() + header.TCPMinimumSize
}
q.mu.Unlock()
return s
}
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