225 Source/Core/DiscIO/MultithreadedCompressor.h
View file
@@ -0,0 +1,225 @@
// Copyright 2020 Dolphin Emulator Project
// Licensed under GPLv2+
// Refer to the license.txt file included.

#pragma once

#include <atomic>
#include <functional>
#include <memory>
#include <thread>
#include <utility>
#include <variant>
#include <vector>

#include "Common/Assert.h"
#include "Common/Event.h"
#include "Common/Result.h"

namespace DiscIO
{
enum class ConversionResultCode
{
Success,
Canceled,
ReadFailed,
WriteFailed,
InternalError,
};

template <typename T>
using ConversionResult = Common::Result<ConversionResultCode, T>;

// This class starts a number of compression threads and one output thread.
// The set_up_compress_thread_state function is called at the start of each compression thread.
// When CompressAndWrite is called, the compress function will be called on one of the
// compression threads, and then the output function will be called on the output thread.
// The output thread handles data in the order that data was submitted using CompressAndWrite,
// but the compression threads are not guaranteed to handle data in a predictable order.
// Remember to check GetStatus regularly and cancel if it doesn't return Success,
// and call Shutdown when you want to ensure that everything finishes.
template <typename CompressThreadState, typename CompressParameters, typename OutputParameters>
class MultithreadedCompressor
{
public:
MultithreadedCompressor(
std::function<ConversionResultCode(CompressThreadState*)> set_up_compress_thread_state,
std::function<ConversionResult<OutputParameters>(CompressThreadState*, CompressParameters)>
compress,
std::function<ConversionResultCode(OutputParameters)> output)
: m_set_up_compress_thread_state(std::move(set_up_compress_thread_state)),
m_compress(std::move(compress)), m_output(std::move(output)),
m_threads(std::max<unsigned int>(1, std::thread::hardware_concurrency()))
{
m_compress_threads = std::make_unique<CompressThread[]>(m_threads);

for (size_t i = 0; i < m_threads; ++i)
{
m_compress_threads[i].thread =
std::thread(std::mem_fn(&MultithreadedCompressor::CompressThreadFunction), this,
&m_compress_threads[i]);
}

m_output_thread =
std::thread(std::mem_fn(&MultithreadedCompressor::OutputThreadFunction), this);
}

~MultithreadedCompressor()
{
if (!m_shutting_down.load())
Shutdown();
}

void CompressAndWrite(CompressParameters parameters)
{
if (GetStatus() != ConversionResultCode::Success)
return;

CompressThread& compress_thread = m_compress_threads[m_current_index];

compress_thread.compress_ready_event.Wait();
compress_thread.compress_parameters = std::move(parameters);
compress_thread.compress_event.Set();

++m_current_index;
if (m_current_index >= m_threads)
m_current_index -= m_threads;
}

void SetError(ConversionResultCode result)
{
ASSERT(result != ConversionResultCode::Success);

// If we already have an error, don't overwrite it
ConversionResultCode expected = ConversionResultCode::Success;
m_result.compare_exchange_strong(expected, result);
}

ConversionResultCode GetStatus() const { return m_result.load(); }

void Shutdown()
{
for (size_t i = 0; i < m_threads; ++i)
m_compress_threads[i].compress_ready_event.Wait();
for (size_t i = 0; i < m_threads; ++i)
m_compress_threads[i].compress_done_event.Wait();
for (size_t i = 0; i < m_threads; ++i)
m_compress_threads[i].output_ready_event.Wait();

m_shutting_down.store(true);

for (size_t i = 0; i < m_threads; ++i)
m_compress_threads[i].compress_event.Set();
for (size_t i = 0; i < m_threads; ++i)
m_compress_threads[i].output_event.Set();

for (size_t i = 0; i < m_threads; ++i)
m_compress_threads[i].thread.join();

m_output_thread.join();
}

private:
struct CompressThread
{
std::thread thread;

Common::Event compress_ready_event;
Common::Event compress_event;
Common::Event compress_done_event;
Common::Event output_ready_event;
Common::Event output_event;

CompressParameters compress_parameters;
OutputParameters output_parameters;
};

void CompressThreadFunction(CompressThread* state)
{
CompressThreadState compress_thread_state;

ConversionResultCode setup_result = m_set_up_compress_thread_state(&compress_thread_state);
if (setup_result != ConversionResultCode::Success)
SetError(setup_result);

state->compress_ready_event.Set();
state->compress_done_event.Set();

while (true)
{
state->compress_event.Wait();

if (m_shutting_down.load())
return;

CompressParameters parameters = std::move(state->compress_parameters);

state->compress_done_event.Reset();
state->compress_ready_event.Set();

ConversionResult<OutputParameters> result =
m_compress(&compress_thread_state, std::move(parameters));

if (result)
{
state->output_ready_event.Wait();
state->output_parameters = std::move(*result);
state->output_event.Set();
}
else
{
SetError(result.Error());
}

state->compress_done_event.Set();
}
}

void OutputThreadFunction()
{
for (size_t i = 0; i < m_threads; ++i)
m_compress_threads[i].output_ready_event.Set();

size_t index = 0;

while (true)
{
CompressThread& compress_thread = m_compress_threads[index];

compress_thread.output_event.Wait();

if (m_shutting_down.load())
return;

OutputParameters parameters = std::move(compress_thread.output_parameters);

compress_thread.output_ready_event.Set();

const ConversionResultCode result = m_output(std::move(parameters));

if (result != ConversionResultCode::Success)
SetError(result);

++index;
if (index >= m_threads)
index -= m_threads;
}
}

std::function<ConversionResultCode(CompressThreadState*)> m_set_up_compress_thread_state;
std::function<ConversionResult<OutputParameters>(CompressThreadState*, CompressParameters)>
m_compress;
std::function<ConversionResultCode(OutputParameters)> m_output;

// We can't use std::vector for this, because Common::Event is not movable
std::unique_ptr<CompressThread[]> m_compress_threads;
std::thread m_output_thread;

const size_t m_threads;
size_t m_current_index = 0;

std::atomic<ConversionResultCode> m_result = ConversionResultCode::Success;
std::atomic<bool> m_shutting_down = false;
};

} // namespace DiscIO