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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 {
namespace platform {
// 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. Whenever the capacity of the
// underlying array changes, Observer::NotifyWriteBufferFill() will be called.
class TlsWriteBuffer {
public:
class Observer {
public:
virtual ~Observer() = default;
// Signals that the write buffer has reached some percentage of being
// filled. NOTE: This method may be called from multiple threads.
virtual void NotifyWriteBufferFill(double fraction) = 0;
};
explicit TlsWriteBuffer(Observer* observer);
~TlsWriteBuffer();
// Writes as much of the provided data as possible in the buffer, returning
// the number of bytes written.
size_t Write(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 << 20; // 1 MB space.
private:
// Signals that the write buffer has reached some percentage of being filled,
// as calculated based on the provided write and read indices.
void NotifyWriteBufferFill(size_t write_index, size_t read_index);
// 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};
Observer* const observer_;
OSP_DISALLOW_COPY_AND_ASSIGN(TlsWriteBuffer);
};
} // namespace platform
} // namespace openscreen
#endif // PLATFORM_IMPL_TLS_WRITE_BUFFER_H_
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