1/*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include "perfetto/protozero/scattered_stream_writer.h"
18
19#include <algorithm>
20
21#include "perfetto/base/logging.h"
22
23namespace protozero {
24
25ScatteredStreamWriter::Delegate::~Delegate() {}
26
27uint8_t* ScatteredStreamWriter::Delegate::AnnotatePatch(uint8_t* patch_addr) {
28 // In most cases, a patch is transparent. The caller can write directly into
29 // `to_patch`, because its memory is not going away. TraceWriterImpl, however,
30 // requires a more complicated logic, because the chunks might be copied
31 // earlier.
32 return patch_addr;
33}
34
35ScatteredStreamWriter::ScatteredStreamWriter(Delegate* delegate)
36 : delegate_(delegate),
37 cur_range_({.begin: nullptr, .end: nullptr}),
38 write_ptr_(nullptr) {}
39
40ScatteredStreamWriter::~ScatteredStreamWriter() {}
41
42void ScatteredStreamWriter::Reset(ContiguousMemoryRange range) {
43 written_previously_ += static_cast<uint64_t>(write_ptr_ - cur_range_.begin);
44 cur_range_ = range;
45 write_ptr_ = range.begin;
46 PERFETTO_DCHECK(!write_ptr_ || write_ptr_ < cur_range_.end);
47}
48
49void ScatteredStreamWriter::Extend() {
50 Reset(range: delegate_->GetNewBuffer());
51}
52
53void ScatteredStreamWriter::WriteBytesSlowPath(const uint8_t* src,
54 size_t size) {
55 size_t bytes_left = size;
56 while (bytes_left > 0) {
57 if (write_ptr_ >= cur_range_.end)
58 Extend();
59 const size_t burst_size = std::min(bytes_available(), bytes_left);
60 WriteBytesUnsafe(src, size: burst_size);
61 bytes_left -= burst_size;
62 src += burst_size;
63 }
64}
65
66// TODO(primiano): perf optimization: I suspect that at the end this will always
67// be called with |size| == 4, in which case we might just hardcode it.
68uint8_t* ScatteredStreamWriter::ReserveBytes(size_t size) {
69 if (write_ptr_ + size > cur_range_.end) {
70 // Assume the reservations are always < Delegate::GetNewBuffer().size(),
71 // so that one single call to Extend() will definitely give enough headroom.
72 Extend();
73 PERFETTO_DCHECK(write_ptr_ + size <= cur_range_.end);
74 }
75 uint8_t* begin = write_ptr_;
76 write_ptr_ += size;
77#if PERFETTO_DCHECK_IS_ON()
78 // In the past, the service had a matching DCHECK in
79 // TraceBuffer::TryPatchChunkContents, which was assuming that service and all
80 // producers are built with matching DCHECK levels. This turned out to be a
81 // source of problems and was removed in b/197340286. This memset is useless
82 // these days and is here only to maintain ABI compatibility between producers
83 // that use a v20+ SDK and older versions of the service that were built in
84 // debug mode. At some point around 2023 it should be safe to remove it.
85 // (running a debug version of traced in production seems a bad idea
86 // regardless).
87 memset(begin, 0, size);
88#endif
89 return begin;
90}
91
92} // namespace protozero
93

source code of dart_sdk/third_party/perfetto/src/protozero/scattered_stream_writer.cc