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52 lines
1.9 KiB
52 lines
1.9 KiB
// Copyright 2021 The Pigweed Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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#include "pw_multisink/drain.h"
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#include "pw_assert/light.h"
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namespace pw {
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namespace multisink {
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Result<ConstByteSpan> Drain::GetEntry(ByteSpan entry,
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uint32_t& drop_count_out) {
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uint32_t entry_sequence_id = 0;
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drop_count_out = 0;
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const Result<ConstByteSpan> result =
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MultiSink::GetEntry(*this, entry, entry_sequence_id);
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// Exit immediately if the result isn't OK or OUT_OF_RANGE, as the
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// entry_sequence_id cannot be used for computation. Later invocations to
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// GetEntry will permit readers to determine how far the sequence ID moved
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// forward.
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if (!result.ok() && !result.status().IsOutOfRange()) {
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return result;
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}
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// Compute the drop count delta by comparing this entry's sequence ID with the
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// last sequence ID this drain successfully read.
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//
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// The drop count calculation simply computes the difference between the
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// current and last sequence IDs. Consecutive successful reads will always
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// differ by one at least, so it is subtracted out. If the read was not
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// successful, the difference is not adjusted.
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drop_count_out =
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entry_sequence_id - last_handled_sequence_id_ - (result.ok() ? 1 : 0);
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last_handled_sequence_id_ = entry_sequence_id;
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return result;
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}
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} // namespace multisink
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} // namespace pw
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