| // Copyright (c) 2017 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef NET_THIRD_PARTY_QUIC_CORE_PACKET_NUMBER_INDEXED_QUEUE_H_ |
| #define NET_THIRD_PARTY_QUIC_CORE_PACKET_NUMBER_INDEXED_QUEUE_H_ |
| |
| #include "net/third_party/quic/core/quic_constants.h" |
| #include "net/third_party/quic/core/quic_types.h" |
| #include "net/third_party/quic/platform/api/quic_bug_tracker.h" |
| #include "net/third_party/quic/platform/api/quic_containers.h" |
| |
| namespace quic { |
| |
| // PacketNumberIndexedQueue is a queue of mostly continuous numbered entries |
| // which supports the following operations: |
| // - adding elements to the end of the queue, or at some point past the end |
| // - removing elements in any order |
| // - retrieving elements |
| // If all elements are inserted in order, all of the operations above are |
| // amortized O(1) time. |
| // |
| // Internally, the data structure is a deque where each element is marked as |
| // present or not. The deque starts at the lowest present index. Whenever an |
| // element is removed, it's marked as not present, and the front of the deque is |
| // cleared of elements that are not present. |
| // |
| // The tail of the queue is not cleared due to the assumption of entries being |
| // inserted in order, though removing all elements of the queue will return it |
| // to its initial state. |
| // |
| // Note that this data structure is inherently hazardous, since an addition of |
| // just two entries will cause it to consume all of the memory available. |
| // Because of that, it is not a general-purpose container and should not be used |
| // as one. |
| template <typename T> |
| class PacketNumberIndexedQueue { |
| public: |
| PacketNumberIndexedQueue() : number_of_present_entries_(0) {} |
| |
| // Retrieve the entry associated with the packet number. Returns the pointer |
| // to the entry in case of success, or nullptr if the entry does not exist. |
| T* GetEntry(QuicPacketNumber packet_number); |
| const T* GetEntry(QuicPacketNumber packet_number) const; |
| |
| // Inserts data associated |packet_number| into (or past) the end of the |
| // queue, filling up the missing intermediate entries as necessary. Returns |
| // true if the element has been inserted successfully, false if it was already |
| // in the queue or inserted out of order. |
| template <typename... Args> |
| bool Emplace(QuicPacketNumber packet_number, Args&&... args); |
| |
| // Removes data associated with |packet_number| and frees the slots in the |
| // queue as necessary. |
| bool Remove(QuicPacketNumber packet_number); |
| |
| bool IsEmpty() const { return number_of_present_entries_ == 0; } |
| |
| // Returns the number of entries in the queue. |
| size_t number_of_present_entries() const { |
| return number_of_present_entries_; |
| } |
| |
| // Returns the number of entries allocated in the underlying deque. This is |
| // proportional to the memory usage of the queue. |
| size_t entry_slots_used() const { return entries_.size(); } |
| |
| // Packet number of the first entry in the queue. |
| QuicPacketNumber first_packet() const { return first_packet_; } |
| |
| // Packet number of the last entry ever inserted in the queue. Note that the |
| // entry in question may have already been removed. Zero if the queue is |
| // empty. |
| QuicPacketNumber last_packet() const { |
| if (IsEmpty()) { |
| return QuicPacketNumber(); |
| } |
| return first_packet_ + entries_.size() - 1; |
| } |
| |
| private: |
| // Wrapper around T used to mark whether the entry is actually in the map. |
| struct EntryWrapper : T { |
| bool present; |
| |
| EntryWrapper() : present(false) {} |
| |
| template <typename... Args> |
| explicit EntryWrapper(Args&&... args) |
| : T(std::forward<Args>(args)...), present(true) {} |
| }; |
| |
| // Cleans up unused slots in the front after removing an element. |
| void Cleanup(); |
| |
| const EntryWrapper* GetEntryWrapper(QuicPacketNumber offset) const; |
| EntryWrapper* GetEntryWrapper(QuicPacketNumber offset) { |
| const auto* const_this = this; |
| return const_cast<EntryWrapper*>(const_this->GetEntryWrapper(offset)); |
| } |
| |
| QuicDeque<EntryWrapper> entries_; |
| size_t number_of_present_entries_; |
| QuicPacketNumber first_packet_; |
| }; |
| |
| template <typename T> |
| T* PacketNumberIndexedQueue<T>::GetEntry(QuicPacketNumber packet_number) { |
| EntryWrapper* entry = GetEntryWrapper(packet_number); |
| if (entry == nullptr) { |
| return nullptr; |
| } |
| return entry; |
| } |
| |
| template <typename T> |
| const T* PacketNumberIndexedQueue<T>::GetEntry( |
| QuicPacketNumber packet_number) const { |
| const EntryWrapper* entry = GetEntryWrapper(packet_number); |
| if (entry == nullptr) { |
| return nullptr; |
| } |
| return entry; |
| } |
| |
| template <typename T> |
| template <typename... Args> |
| bool PacketNumberIndexedQueue<T>::Emplace(QuicPacketNumber packet_number, |
| Args&&... args) { |
| if (!packet_number.IsInitialized()) { |
| QUIC_BUG << "Try to insert an uninitialized packet number"; |
| return false; |
| } |
| |
| if (IsEmpty()) { |
| DCHECK(entries_.empty()); |
| DCHECK(!first_packet_.IsInitialized()); |
| |
| entries_.emplace_back(std::forward<Args>(args)...); |
| number_of_present_entries_ = 1; |
| first_packet_ = packet_number; |
| return true; |
| } |
| |
| // Do not allow insertion out-of-order. |
| if (packet_number <= last_packet()) { |
| return false; |
| } |
| |
| // Handle potentially missing elements. |
| size_t offset = packet_number - first_packet_; |
| if (offset > entries_.size()) { |
| entries_.resize(offset); |
| } |
| |
| number_of_present_entries_++; |
| entries_.emplace_back(std::forward<Args>(args)...); |
| DCHECK_EQ(packet_number, last_packet()); |
| return true; |
| } |
| |
| template <typename T> |
| bool PacketNumberIndexedQueue<T>::Remove(QuicPacketNumber packet_number) { |
| EntryWrapper* entry = GetEntryWrapper(packet_number); |
| if (entry == nullptr) { |
| return false; |
| } |
| entry->present = false; |
| number_of_present_entries_--; |
| |
| if (packet_number == first_packet()) { |
| Cleanup(); |
| } |
| return true; |
| } |
| |
| template <typename T> |
| void PacketNumberIndexedQueue<T>::Cleanup() { |
| while (!entries_.empty() && !entries_.front().present) { |
| entries_.pop_front(); |
| first_packet_++; |
| } |
| if (entries_.empty()) { |
| first_packet_.Clear(); |
| } |
| } |
| |
| template <typename T> |
| auto PacketNumberIndexedQueue<T>::GetEntryWrapper( |
| QuicPacketNumber packet_number) const -> const EntryWrapper* { |
| if (!packet_number.IsInitialized() || IsEmpty() || |
| packet_number < first_packet_) { |
| return nullptr; |
| } |
| |
| uint64_t offset = packet_number - first_packet_; |
| if (offset >= entries_.size()) { |
| return nullptr; |
| } |
| |
| const EntryWrapper* entry = &entries_[offset]; |
| if (!entry->present) { |
| return nullptr; |
| } |
| |
| return entry; |
| } |
| |
| } // namespace quic |
| |
| #endif // NET_THIRD_PARTY_QUIC_CORE_PACKET_NUMBER_INDEXED_QUEUE_H_ |