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tdutils/td/utils/MpscPollableQueue.h

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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
+*/
+#pragma once
+
+#include "td/utils/common.h"
+#include "td/utils/misc.h"
+#include "td/utils/port/EventFd.h"
+
+#if !TD_EVENTFD_UNSUPPORTED
+
+#include "td/utils/SpinLock.h"
+
+#include <utility>
+
+namespace td {
+// interface like in PollableQueue
+template <class T>
+class MpscPollableQueue {
+ public:
+  using ValueType = T;
+
+  int reader_wait_nonblock() {
+    auto ready = reader_vector_.size() - reader_pos_;
+    if (ready != 0) {
+      return narrow_cast<int>(ready);
+    }
+
+    for (int i = 0; i < 2; i++) {
+      auto guard = lock_.lock();
+      if (writer_vector_.empty()) {
+        if (i == 1) {
+          wait_event_fd_ = true;
+          return 0;
+        }
+      } else {
+        reader_vector_.clear();
+        reader_pos_ = 0;
+        std::swap(writer_vector_, reader_vector_);
+        return narrow_cast<int>(reader_vector_.size());
+      }
+      event_fd_.acquire();
+    }
+    UNREACHABLE();
+  }
+  ValueType reader_get_unsafe() {
+    return std::move(reader_vector_[reader_pos_++]);
+  }
+  void reader_flush() {
+    //nop
+  }
+  void writer_put(ValueType value) {
+    auto guard = lock_.lock();
+    writer_vector_.push_back(std::move(value));
+    if (wait_event_fd_) {
+      wait_event_fd_ = false;
+      guard.reset();
+      event_fd_.release();
+    }
+  }
+  EventFd &reader_get_event_fd() {
+    return event_fd_;
+  }
+  void writer_flush() {
+    //nop
+  }
+
+  void init() {
+    event_fd_.init();
+  }
+  void destroy() {
+    if (!event_fd_.empty()) {
+      event_fd_.close();
+      wait_event_fd_ = false;
+      writer_vector_.clear();
+      reader_vector_.clear();
+      reader_pos_ = 0;
+    }
+  }
+
+  // Just an example of usage
+  int reader_wait() {
+    int res;
+    while ((res = reader_wait_nonblock()) == 0) {
+      reader_get_event_fd().wait(1000);
+    }
+    return res;
+  }
+
+ private:
+  SpinLock lock_;
+  bool wait_event_fd_{false};
+  EventFd event_fd_;
+  std::vector<ValueType> writer_vector_;
+  std::vector<ValueType> reader_vector_;
+  size_t reader_pos_{0};
+};
+
+}  // namespace td
+
+#else
+
+namespace td {
+
+// dummy implementation which shouldn't be used
+
+template <class T>
+class MpscPollableQueue {
+ public:
+  using ValueType = T;
+
+  void init() {
+    UNREACHABLE();
+  }
+
+  template <class PutValueType>
+  void writer_put(PutValueType &&value) {
+    UNREACHABLE();
+  }
+
+  void writer_flush() {
+    UNREACHABLE();
+  }
+
+  int reader_wait_nonblock() {
+    UNREACHABLE();
+    return 0;
+  }
+
+  ValueType reader_get_unsafe() {
+    UNREACHABLE();
+    return ValueType();
+  }
+
+  void reader_flush() {
+    UNREACHABLE();
+  }
+
+  MpscPollableQueue() = default;
+  MpscPollableQueue(const MpscPollableQueue &) = delete;
+  MpscPollableQueue &operator=(const MpscPollableQueue &) = delete;
+  MpscPollableQueue(MpscPollableQueue &&) = delete;
+  MpscPollableQueue &operator=(MpscPollableQueue &&) = delete;
+  ~MpscPollableQueue() = default;
+};
+
+}  // namespace td
+
+#endif