| // 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 tcp |
| |
| import ( |
| "gvisor.dev/gvisor/pkg/sync" |
| ) |
| |
| // segmentQueue is a bounded, thread-safe queue of TCP segments. |
| // |
| // +stateify savable |
| type segmentQueue struct { |
| mu sync.Mutex `state:"nosave"` |
| list segmentList `state:"wait"` |
| ep *endpoint |
| frozen bool |
| } |
| |
| // emptyLocked determines if the queue is empty. |
| // Preconditions: q.mu must be held. |
| func (q *segmentQueue) emptyLocked() bool { |
| return q.list.Empty() |
| } |
| |
| // empty determines if the queue is empty. |
| func (q *segmentQueue) empty() bool { |
| q.mu.Lock() |
| r := q.emptyLocked() |
| q.mu.Unlock() |
| |
| return r |
| } |
| |
| // 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.ep.receiveBufferParams() must be called without holding q.mu to |
| // avoid lock order inversion. |
| bufSz := q.ep.receiveBufferSize() |
| used := q.ep.receiveMemUsed() |
| q.mu.Lock() |
| // Allow zero sized segments (ACK/FIN/RSTs etc even if the segment queue |
| // is currently full). |
| allow := (used <= bufSz || s.payloadSize() == 0) && !q.frozen |
| |
| if allow { |
| q.list.PushBack(s) |
| // Set the owner now that the endpoint owns the segment. |
| s.setOwner(q.ep, recvQ) |
| } |
| q.mu.Unlock() |
| |
| return allow |
| } |
| |
| // 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.mu.Unlock() |
| |
| return s |
| } |
| |
| // freeze prevents any more segments from being added to the queue. i.e all |
| // future segmentQueue.enqueue will return false and not add the segment to the |
| // queue till the queue is unfroze with a corresponding segmentQueue.thaw call. |
| func (q *segmentQueue) freeze() { |
| q.mu.Lock() |
| q.frozen = true |
| q.mu.Unlock() |
| } |
| |
| // thaw unfreezes a previously frozen queue using segmentQueue.freeze() and |
| // allows new segments to be queued again. |
| func (q *segmentQueue) thaw() { |
| q.mu.Lock() |
| q.frozen = false |
| q.mu.Unlock() |
| } |