選択できるのは25トピックまでです。
トピックは、先頭が英数字で、英数字とダッシュ('-')を使用した35文字以内のものにしてください。
201 行
5.9 KiB
201 行
5.9 KiB
#pragma once
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#include <cstddef>
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#include <atomic>
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#include <new>
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#include <cassert>
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#include <optional>
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#ifdef __cpp_lib_hardware_interference_size
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static constexpr size_t max_interference_size = std::max(std::hardware_constructive_interference_size, std::hardware_destructive_interference_size);
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static constexpr size_t line_length = std::hardware_constructive_interference_size;
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#else
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static constexpr size_t max_interference_size = 128;
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static constexpr size_t line_length = 64;
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#endif
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template<typename T>
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struct alignas(max_interference_size) padded_atomic final {
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std::atomic<T> value;
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};
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using offset_t = size_t;
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extern const size_t page_size;
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enum class overflow_response_t {
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must_wait,
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must_overflow
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};
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#ifdef __cpp_concepts
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template<typename T>
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concept OverflowStrategyType = requires (T strategy) {
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{T::on_overflow} -> std::same_as<overflow_response_t>;
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{strategy.wait()};
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};
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#endif
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struct force_contiguous_mode {};
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struct token_t {offset_t start; offset_t end;};
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struct disruptor_exception : public std::runtime_error {
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disruptor_exception() : std::runtime_error("Unknown error disruptor") {}
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explicit disruptor_exception(const char* str) : std::runtime_error(str) {}
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};
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template<typename OverflowStrategy>
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#ifdef __cpp_concepts
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requires OverflowStrategyType<OverflowStrategy>
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#endif
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class disruptor
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{
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char* buffer;
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size_t buffer_size;
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std::atomic<offset_t>& read_trailer;
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std::atomic<offset_t>& read_lead;
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std::atomic<offset_t>& write_trailer;
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std::atomic<offset_t>& write_lead;
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offset_t& max_offset;
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char* data_buffer;
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public:
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disruptor(char* _buffer, const size_t _buffer_size)
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: buffer(_buffer)
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, buffer_size(_buffer_size)
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, read_trailer (*reinterpret_cast<std::atomic<offset_t>*>(_buffer+max_interference_size*0))
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, read_lead (*reinterpret_cast<std::atomic<offset_t>*>(_buffer+max_interference_size*1))
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, write_trailer(*reinterpret_cast<std::atomic<offset_t>*>(_buffer+max_interference_size*2))
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, write_lead (*reinterpret_cast<std::atomic<offset_t>*>(_buffer+max_interference_size*3))
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, max_offset (*reinterpret_cast<offset_t*> (_buffer+max_interference_size*4))
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{
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if(buffer_size <= page_size) throw disruptor_exception("buffer size too small to build a disruptor");
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data_buffer = buffer+max_interference_size*5;
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if(data_buffer <= buffer+page_size) {
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data_buffer = buffer+page_size;
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max_offset = buffer_size - page_size;
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} else if(data_buffer > buffer+page_size) {
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size_t ctr = 0;
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do {
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ctr++;
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} while(data_buffer > buffer+page_size*ctr);
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data_buffer = buffer+page_size*ctr;
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max_offset = buffer_size - page_size*ctr;
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}
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}
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template<bool must_be_contiguous = false>
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std::optional<token_t> try_advance(
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std::atomic<offset_t>& lead,
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std::atomic<offset_t> fence,
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offset_t amount
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) {
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offset_t old_offset = lead.load(std::memory_order_relaxed);
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offset_t new_offset = old_offset + amount;
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offset_t fence_v = fence.load(std::memory_order_relaxed);
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// Check if we jumped the fence
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if(fence_v <= new_offset && fence_v > old_offset) {
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goto handle_fence;
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}
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// Check if we jumped the fence while overflowing
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if(new_offset >= max_offset) {
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if constexpr(must_be_contiguous) {
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new_offset = amount;
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} else {
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new_offset %= max_offset;
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}
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if(fence_v <= new_offset) {
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goto handle_fence;
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}
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}
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goto handle_fence_end;
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handle_fence:
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if constexpr (OverflowStrategy::on_overflow == overflow_response_t::must_wait) {
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return std::nullopt;
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} else if constexpr (OverflowStrategy::on_overflow == overflow_response_t::must_overflow) {
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if(!fence.compare_exchange_weak(fence_v, new_offset, std::memory_order_release, std::memory_order_relaxed)) {
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return std::nullopt;
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} else {
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offset_t v;
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do {
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v = read_lead.load(std::memory_order_acquire);
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if(v >= new_offset) break;
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} while(read_lead.compare_exchange_weak(v, new_offset, std::memory_order_release, std::memory_order_relaxed));
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}
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} else {
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static_assert(
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OverflowStrategy::on_overflow == overflow_response_t::must_wait
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|| OverflowStrategy::on_overflow == overflow_response_t::must_overflow
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);
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}
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handle_fence_end:
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if(!lead.compare_exchange_weak(old_offset, new_offset, std::memory_order_acquire, std::memory_order_relaxed)) {
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return std::nullopt;
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}
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return token_t{old_offset, new_offset};
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}
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token_t reserve_write(size_t sz) {
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std::optional<token_t> tok;
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OverflowStrategy waiter;
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while(true) {
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tok = try_advance(write_lead, read_trailer, sz);
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if(tok) break;
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waiter.wait();
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}
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return tok.value();
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}
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token_t reserve_write(size_t sz, force_contiguous_mode) {
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std::optional<token_t> tok;
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OverflowStrategy waiter;
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while(true) {
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tok = try_advance<true>(write_lead, read_trailer, sz);
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if(tok) break;
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waiter.wait();
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}
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return tok.value();
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}
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void conclude_write(token_t tok) noexcept(std::is_nothrow_invocable_v<typename OverflowStrategy::wait>) {
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OverflowStrategy waiter;
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while(!write_trailer.compare_exchange_weak(tok.start, tok.end, std::memory_order_release, std::memory_order_relaxed)) {
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waiter.wait();
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}
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}
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token_t reserve_read() {
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offset_t old_offset = read_lead.load(std::memory_order_relaxed);
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offset_t new_offset = write_trailer.load(std::memory_order_relaxed);
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if(old_offset > new_offset) new_offset = 0;
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OverflowStrategy waiter;
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while(!read_lead.compare_exchange_weak(old_offset, new_offset, std::memory_order_acquire, std::memory_order_relaxed)) {
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waiter.wait();
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}
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return token_t{old_offset, new_offset};
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}
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void conclude_read(token_t tok) noexcept(std::is_nothrow_invocable_v<typename OverflowStrategy::wait>) {
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OverflowStrategy waiter;
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while(!read_trailer.compare_exchange_weak(tok.start, tok.end, std::memory_order_release, std::memory_order_relaxed)) {
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waiter.wait();
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}
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}
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};
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struct OverflowWait {
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static constexpr overflow_response_t on_overflow = overflow_response_t::must_wait;
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void wait() {
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#ifdef __clang__ or __GNUC__
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__asm__("nop\n\t");
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#elif _MSC_VER
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__nop;
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#endif
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}
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};
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