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tddb/td/db/utils/CyclicBuffer.cpp

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+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2017-2019 Telegram Systems LLP
+*/
+#include "CyclicBuffer.h"
+
+#include "td/utils/misc.h"
+#include "td/utils/Slice.h"
+
+#include <atomic>
+#include <limits>
+#include <memory>
+
+namespace td {
+namespace detail {
+class CyclicBuffer : public StreamWriterInterface, public StreamReaderInterface {
+ public:
+  using Options = ::td::CyclicBuffer::Options;
+
+  CyclicBuffer(Options options) {
+    CHECK(options.chunk_size != 0);
+    CHECK(options.count != 0);
+    CHECK(options.alignment != 0);
+    CHECK(options.chunk_size < (std::numeric_limits<size_t>::max() - options.alignment) / options.count);
+    shared_.options_ = options;
+    shared_.raw_data_ = std::make_unique<char[]>(options.size() + options.alignment - 1);
+    auto pos = reinterpret_cast<uint64>(shared_.raw_data_.get());
+    auto offset = (options.alignment - static_cast<size_t>(pos % options.alignment)) % options.alignment;
+    CHECK(offset < options.alignment);
+    shared_.data_ = MutableSlice(shared_.raw_data_.get() + offset, options.size());
+  }
+
+  // StreamReaderInterface
+  size_t reader_size() override {
+    auto offset = reader_.pos_.load(std::memory_order_relaxed);
+    auto size = writer_.pos_.load(std::memory_order_acquire) - offset;
+    return narrow_cast<size_t>(size);
+  }
+  Slice prepare_read() override {
+    auto offset = reader_.pos_.load(std::memory_order_relaxed);
+    auto size = narrow_cast<size_t>(writer_.pos_.load(std::memory_order_acquire) - offset);
+    if (size == 0) {
+      return {};
+    }
+    offset %= (shared_.options_.chunk_size * shared_.options_.count);
+    return shared_.data_.substr(narrow_cast<size_t>(offset)).truncate(size).truncate(shared_.options_.chunk_size);
+  }
+  Span<IoSlice> prepare_readv() override {
+    reader_.io_slice_ = as_io_slice(prepare_read());
+    return Span<IoSlice>(&reader_.io_slice_, 1);
+  }
+  void confirm_read(size_t size) override {
+    reader_.pos_.store(reader_.pos_.load(std::memory_order_relaxed) + size);
+  }
+
+  void close_reader(Status error) override {
+    CHECK(!reader_.is_closed_);
+    reader_.status_ = std::move(error);
+    reader_.is_closed_.store(true, std::memory_order_release);
+  }
+  bool is_writer_closed() const override {
+    return writer_.is_closed_.load(std::memory_order_acquire);
+  }
+  Status &writer_status() override {
+    CHECK(is_writer_closed());
+    return writer_.status_;
+  }
+
+  // StreamWriterInterface
+  size_t writer_size() override {
+    auto offset = reader_.pos_.load(std::memory_order_acquire);
+    auto size = writer_.pos_.load(std::memory_order_relaxed) - offset;
+    return narrow_cast<size_t>(size);
+  }
+  MutableSlice prepare_write() override {
+    auto max_offset =
+        reader_.pos_.load(std::memory_order_acquire) + shared_.options_.chunk_size * (shared_.options_.count - 1);
+    auto offset = writer_.pos_.load(std::memory_order_relaxed);
+    if (offset > max_offset) {
+      return {};
+    }
+    offset %= (shared_.options_.chunk_size * shared_.options_.count);
+    return shared_.data_.substr(narrow_cast<size_t>(offset), shared_.options_.chunk_size);
+  }
+  MutableSlice prepare_write_at_least(size_t size) override {
+    UNREACHABLE();
+  }
+  void confirm_write(size_t size) override {
+    writer_.pos_.store(writer_.pos_.load(std::memory_order_relaxed) + size);
+  }
+  void append(Slice data) override {
+    UNREACHABLE();
+  }
+  void append(BufferSlice data) override {
+    UNREACHABLE();
+  }
+  void append(std::string data) override {
+    UNREACHABLE();
+  }
+  void close_writer(Status error) override {
+    CHECK(!writer_.is_closed_);
+    writer_.status_ = std::move(error);
+    writer_.is_closed_.store(true, std::memory_order_release);
+  }
+  bool is_reader_closed() const override {
+    return reader_.is_closed_.load(std::memory_order_acquire);
+  }
+  Status &reader_status() override {
+    CHECK(is_reader_closed());
+    return reader_.status_;
+  }
+
+ private:
+  struct SharedData {
+    std::unique_ptr<char[]> raw_data_;
+    MutableSlice data_;
+    Options options_;
+  } shared_;
+
+  struct ReaderData {
+    std::atomic<uint64> pos_{0};
+    std::atomic<bool> is_closed_{false};
+    Status status_;
+    IoSlice io_slice_;
+  } reader_;
+
+  char pad[128];
+
+  struct WriterData {
+    std::atomic<uint64> pos_{0};
+    std::atomic<bool> is_closed_{false};
+    Status status_;
+  } writer_;
+};
+}  // namespace detail
+
+std::pair<CyclicBuffer::Reader, CyclicBuffer::Writer> CyclicBuffer::create(Options options) {
+  auto impl = std::make_shared<detail::CyclicBuffer>(options);
+  return {Reader(impl), Writer(impl)};
+}
+}  // namespace td