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// Copyright 2019 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 PLATFORM_IMPL_TLS_WRITE_BUFFER_H_
#define PLATFORM_IMPL_TLS_WRITE_BUFFER_H_
#include <atomic>
#include <memory>
#include "absl/types/span.h"
#include "platform/base/macros.h"
namespace openscreen {
// This class is responsible for buffering TLS Write data. The approach taken by
// this class is to allow for a single thread to act as a publisher of data and
// for a separate thread to act as the consumer of that data. The data in
// question is written to a lockless FIFO queue.
class TlsWriteBuffer {
public:
TlsWriteBuffer();
~TlsWriteBuffer();
// Pushes the provided data into the buffer, returning true if successful.
// Returns false if there was insufficient space left. Either all or none of
// the data is pushed into the buffer.
bool Push(const void* data, size_t len);
// Returns a subset of the readable region of data. At time of reading, more
// data may be available for reading than what is represented in this Span.
absl::Span<const uint8_t> GetReadableRegion();
// Marks the provided number of bytes as consumed by the consumer thread.
void Consume(size_t byte_count);
// The amount of space to allocate in the buffer.
static constexpr size_t kBufferSizeBytes = 1 << 19; // 0.5 MB.
private:
// Buffer where data to be written over the TLS connection is stored.
uint8_t buffer_[kBufferSizeBytes];
// Total number of bytes read or written so far. Atomics are used both to
// ensure that read and write operations are atomic for uint64s on all systems
// and to ensure that different values for these values aren't loaded from
// each CPU's physical cache.
std::atomic_size_t bytes_read_so_far_{0};
std::atomic_size_t bytes_written_so_far_{0};
OSP_DISALLOW_COPY_AND_ASSIGN(TlsWriteBuffer);
};
} // namespace openscreen
#endif // PLATFORM_IMPL_TLS_WRITE_BUFFER_H_
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