blob: e4548c5c3958fe373e719610faaa927936f82317 [file] [log] [blame]
// Copyright 2021 The Pigweed 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
// 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.
#include "pw_multisink/drain.h"
namespace pw {
namespace multisink {
Result<ConstByteSpan> Drain::GetEntry(ByteSpan entry,
uint32_t& drop_count_out) {
uint32_t entry_sequence_id = 0;
drop_count_out = 0;
const Result<ConstByteSpan> result =
MultiSink::GetEntry(*this, entry, entry_sequence_id);
// Exit immediately if the result isn't OK or OUT_OF_RANGE, as the
// entry_sequence_id cannot be used for computation. Later invocations to
// GetEntry will permit readers to determine how far the sequence ID moved
// forward.
if (!result.ok() && !result.status().IsOutOfRange()) {
return result;
// Compute the drop count delta by comparing this entry's sequence ID with the
// last sequence ID this drain successfully read.
// The drop count calculation simply computes the difference between the
// current and last sequence IDs. Consecutive successful reads will always
// differ by one at least, so it is subtracted out. If the read was not
// successful, the difference is not adjusted.
drop_count_out =
entry_sequence_id - last_handled_sequence_id_ - (result.ok() ? 1 : 0);
last_handled_sequence_id_ = entry_sequence_id;
return result;
} // namespace multisink
} // namespace pw