log_ring_buffer.h | Explore in Territory

/*
 * Copyright (C) 2021 The Android Open Source Project
 *
 * 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
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * 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.
 */

#ifndef SRC_BASE_LOG_RING_BUFFER_H_
#define SRC_BASE_LOG_RING_BUFFER_H_

#include <stddef.h>
#include <stdio.h>

#include <array>
#include <atomic>

#include "perfetto/ext/base/string_view.h"
#include "perfetto/ext/base/thread_annotations.h"

namespace perfetto {
namespace base {

// Defined out of line because a static constexpr requires static storage if
// ODR-used, not worth adding a .cc file just for tests.
constexpr size_t kLogRingBufEntries = …;
constexpr size_t kLogRingBufMsgLen = …;

// A static non-allocating ring-buffer to hold the most recent log events.
// This class is really an implementation detail of logging.cc. The only reason
// why is fully defined in a dedicated header is for allowing unittesting,
// without leaking extra headers into logging.h (which is a high-fanout header).
// This is used to report the last logs in a crash report when a CHECK/FATAL
// is encountered.
// This class has just an Append() method to insert events into the buffer and
// a Read() to read the events in FIFO order. Read() is non-destructive.
//
// Thread safety considerations:
// - The Append() method can be called concurrently by several threads, unless
//   there are > kLogRingBufEntries concurrent threads. Even if that happens,
//   case some events will contain a mix of strings but the behavior of
//   futher Append() and Read() is still defined.
// - The Read() method is not thread safe but it's fine in practice. Even if
//   it's called concurrently with other Append(), it only causes some partial
//   events to be emitted in output.
// In both cases, we never rely purely on \0, all operations are size-bound.
//
// See logging_unittest.cc for tests.
class LogRingBuffer { … };

}  // namespace base
}  // namespace perfetto

#endif  // SRC_BASE_LOG_RING_BUFFER_H_
chromium/third_party/perfetto/src/base/log_ring_buffer.h
