1 // Copyright 2021 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14 #include "pw_multisink/drain.h"
15
16 #include "pw_assert/light.h"
17
18 namespace pw {
19 namespace multisink {
20
GetEntry(ByteSpan entry,uint32_t & drop_count_out)21 Result<ConstByteSpan> Drain::GetEntry(ByteSpan entry,
22 uint32_t& drop_count_out) {
23 uint32_t entry_sequence_id = 0;
24 drop_count_out = 0;
25 const Result<ConstByteSpan> result =
26 MultiSink::GetEntry(*this, entry, entry_sequence_id);
27
28 // Exit immediately if the result isn't OK or OUT_OF_RANGE, as the
29 // entry_sequence_id cannot be used for computation. Later invocations to
30 // GetEntry will permit readers to determine how far the sequence ID moved
31 // forward.
32 if (!result.ok() && !result.status().IsOutOfRange()) {
33 return result;
34 }
35
36 // Compute the drop count delta by comparing this entry's sequence ID with the
37 // last sequence ID this drain successfully read.
38 //
39 // The drop count calculation simply computes the difference between the
40 // current and last sequence IDs. Consecutive successful reads will always
41 // differ by one at least, so it is subtracted out. If the read was not
42 // successful, the difference is not adjusted.
43 drop_count_out =
44 entry_sequence_id - last_handled_sequence_id_ - (result.ok() ? 1 : 0);
45
46 last_handled_sequence_id_ = entry_sequence_id;
47 return result;
48 }
49
50 } // namespace multisink
51 } // namespace pw
52