Add async message processing

libfuse/lib/thread_pool.hpp

@@ -0,0 +1,112 @@
+#pragma once
+
+#include "unbounded_queue.hpp"
+
+#include <tuple>
+#include <atomic>
+#include <vector>
+#include <thread>
+#include <memory>
+#include <future>
+#include <utility>
+#include <functional>
+#include <type_traits>
+
+
+class ThreadPool
+{
+public:
+  explicit
+  ThreadPool(const std::size_t thread_count_ = std::thread::hardware_concurrency())
+    : _queues(thread_count_),
+      _count(thread_count_)
+  {
+    auto worker = [this](std::size_t i)
+    {
+      while(true)
+        {
+          Proc f;
+
+          for(std::size_t n = 0; n < (_count * K); ++n)
+            {
+              if(_queues[(i + n) % _count].try_pop(f))
+                break;
+            }
+
+          if(!f && !_queues[i].pop(f))
+            break;
+
+          f();
+        }
+    };
+
+    _threads.reserve(thread_count_);
+    for(std::size_t i = 0; i < thread_count_; ++i)
+      _threads.emplace_back(worker, i);
+  }
+
+  ~ThreadPool()
+  {
+    for(auto& queue : _queues)
+      queue.unblock();
+    for(auto& thread : _threads)
+      thread.join();
+  }
+
+  template<typename F>
+  void
+  enqueue_work(F&& f_)
+  {
+    auto i = _index++;
+
+    for(std::size_t n = 0; n < (_count * K); ++n)
+      {
+        if(_queues[(i + n) % _count].try_push(f_))
+          return;
+      }
+
+    _queues[i % _count].push(std::move(f_));
+  }
+
+  template<typename F>
+  [[nodiscard]]
+  std::future<typename std::result_of<F()>::type>
+  enqueue_task(F&& f_)
+  {
+    using TaskReturnType = typename std::result_of<F()>::type;
+    using Promise        = std::promise<TaskReturnType>;
+
+    auto i       = _index++;
+    auto promise = std::make_shared<Promise>();
+    auto future  = promise->get_future();
+    auto work    = [=]() {
+      auto rv = f_();
+      promise->set_value(rv);
+    };
+
+    for(std::size_t n = 0; n < (_count * K); ++n)
+      {
+        if(_queues[(i + n) % _count].try_push(work))
+          return future;
+      }
+
+    _queues[i % _count].push(std::move(work));
+
+    return future;
+  }
+
+private:
+  using Proc   = std::function<void(void)>;
+  using Queue  = UnboundedQueue<Proc>;
+  using Queues = std::vector<Queue>;
+  Queues _queues;
+
+private:
+  std::vector<std::thread> _threads;
+
+private:
+  const std::size_t _count;
+  std::atomic_uint _index;
+
+  static const unsigned int K = 2;
+};