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// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef COMPONENTS_TRACING_CORE_TRACE_RING_BUFFER_H_
#define COMPONENTS_TRACING_CORE_TRACE_RING_BUFFER_H_
#include <memory>
#include "base/atomicops.h"
#include "base/macros.h"
#include "base/synchronization/lock.h"
#include "components/tracing/tracing_export.h"
namespace tracing {
namespace v2 {
static const uint32_t kNoChunkOwner = 0;
static const size_t kChunkSize = 32 * 1024;
class TRACING_EXPORT TraceRingBuffer {
public:
class Chunk {
public:
using Header = base::subtle::Atomic32;
Chunk();
~Chunk();
void Initialize(uint8_t* begin);
void Clear();
uint8_t* begin() const { return begin_; }
Header* header() const { return reinterpret_cast<Header*>(begin_); }
uint8_t* payload() const { return begin_ + sizeof(Header); }
uint8_t* end() const { return begin_ + kChunkSize; }
void set_used_size(uint32_t size) {
base::subtle::NoBarrier_Store(header(), size);
}
uint32_t used_size() const {
return base::subtle::NoBarrier_Load(header());
}
void set_next_in_owner_list(Chunk* next) { next_in_owner_list_ = next; }
Chunk* next_in_owner_list() const { return next_in_owner_list_; }
// Owner is a flag matching the id of the TraceBufferWriter, 0 if not owned.
// Accesses to |owner_| must happen under the buffer |lock_|.
bool is_owned() const { return owner_ != kNoChunkOwner; }
uint32_t owner() const { return owner_; }
void clear_owner() { owner_ = kNoChunkOwner; }
void set_owner(uint32_t owner) {
DCHECK_NE(kNoChunkOwner, owner);
owner_ = owner;
}
private:
uint8_t* begin_;
uint32_t owner_;
// When a chunk is owned, this is the next pointer to keep track of all
// owned chunks in a singly linked list.
Chunk* next_in_owner_list_;
DISALLOW_COPY_AND_ASSIGN(Chunk);
};
TraceRingBuffer(uint8_t* begin, size_t size);
~TraceRingBuffer();
Chunk* TakeChunk(uint32_t writer_id);
void ReturnChunk(Chunk* chunk);
size_t num_chunks() const { return num_chunks_; }
// Returns the number of chunks taken and not returned, without counting any
// bankrupcy chunk obtained when the ring buffer was full.
size_t GetNumChunksTaken() const;
const Chunk* chunks_for_testing() const { return chunks_.get(); }
bool IsBankrupcyChunkForTesting(const Chunk*) const;
private:
mutable base::Lock lock_;
std::unique_ptr<Chunk[]> chunks_;
const size_t num_chunks_;
size_t num_chunks_taken_;
size_t current_chunk_idx_;
// An emergency chunk used in the rare case in which all chunks are in flight.
// This chunk is not part of the ring buffer and its contents are always
// discarded. Its only purpose is to avoid a crash (due to TakeChunk returning
// nullptr) in the case of a thread storm.
Chunk bankrupcy_chunk_;
std::unique_ptr<uint8_t[]> bankrupcy_chunk_storage_;
DISALLOW_COPY_AND_ASSIGN(TraceRingBuffer);
};
} // namespace v2
} // namespace tracing
#endif // COMPONENTS_TRACING_CORE_TRACE_RING_BUFFER_H_
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