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// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <cstdint>
#include <type_traits>
#include "ipcz/monitored_atomic.h"
namespace ipcz {
// AtomicQueueState holds some trivial data about how much of a router's inbound
// parcel sequence has been consumed so far.
// Note that the fields herein are not strictly synchronized. If a queue
// accumulates a 4k parcel and an 8k parcel which are both then consumed by the
// application, the remote sender may observe `num_parcels_consumed` at 0, then
// 1, then 2; and they may observe `num_bytes_consumed` at 0, then 4k, and then
// 12k; the ordering of those individual progressions is guaranteed, but there's
// no guarantee that an observer will see `num_parcels_consumed` as 1 at the
// same time they see `num_bytes_consumed` as 4k.
class alignas(8) AtomicQueueState {
AtomicQueueState() noexcept;
// Performs a best-effort query of the most recently visible value on both
// fields and returns them as a QueryResult. `monitors` determines whether
// each field will be atomically marked for monitoring at the same time its
// value is retrieved.
struct QueryResult {
MonitoredAtomic<uint64_t>::State num_parcels_consumed;
MonitoredAtomic<uint64_t>::State num_bytes_consumed;
struct MonitorSelection {
bool monitor_parcels;
bool monitor_bytes;
QueryResult Query(const MonitorSelection& monitors);
// Updates both fields with new values, resetting any monitor bit that may
// have been set on either one. If either field had a monitor bit set prior to
// this update, this returns true. Otherwise it returns false.
struct UpdateValue {
uint64_t num_parcels_consumed;
uint64_t num_bytes_consumed;
bool Update(const UpdateValue& value);
// The number of parcels consumed from the router's inbound parcel queue,
// either by the application reading from its portal, or by ipcz proxying them
// onward to another router.
MonitoredAtomic<uint64_t> num_parcels_consumed_{0};
// The total number of bytes of data consumed from the router's inbound parcel
// queue. This is the sum of the data size of all parcels covered by
// `consumed_sequence_length`, plus any bytes already consumed from the
// next parcel in sequence if it's been partially consumed..
MonitoredAtomic<uint64_t> num_bytes_consumed_{0};
// This must remain stable at 16 bytes in size, as it's part of shared memory
// layouts. Trivial copyability is also required as a proxy condition to prevent
// changes which might break that usage (e.g. introduction of a non-trivial
// destructor.)
static_assert(sizeof(AtomicQueueState) == 16, "Invalid AtomicQueueState size");
"AtomicQueueState must be trivially copyable");
} // namespace ipcz