Improve scheduler:

- Let thieves remove empty suspended deques from pools
- When enabling empty suspended deques, reinsert them in a pool
- Use direct locking when suspending and enabling

rt/include/typon/core/deque.hpp

@@ -20,17 +20,19 @@ namespace typon
 
     using enum std::memory_order;
 
+    enum State : unsigned char { Empty, Suspended, Resumable };
+
     std::atomic<u64> _top {1};
     std::atomic<u64> _bottom {1};
     std::atomic<ring_buffer *> _buffer { new ring_buffer(3) };
     std::coroutine_handle<> _coroutine;
-    std::atomic<bool> _resumable;
+    std::atomic<State> _state;
 
     Deque() noexcept {}
 
     Deque(std::coroutine_handle<> coroutine) noexcept
       : _coroutine(coroutine)
-      , _resumable(true)
+      , _state(Resumable)
     {}
 
     ~Deque()
@@ -107,7 +109,7 @@ namespace typon
 
     void suspend(std::coroutine_handle<> coroutine) noexcept
     {
-      _resumable.store(false);
+      _state.store(Suspended);
       _coroutine = coroutine;
     }
 

rt/include/typon/core/scheduler.hpp

@@ -44,17 +44,17 @@ namespace typon
 
     static void push(Continuation task) noexcept
     {
-      get()._worker[thread_id]._active.load()->push(task);
+      get()._worker[thread_id]._deque.load()->push(task);
     }
 
     static bool pop() noexcept
     {
       Scheduler & scheduler = get();
-      Deque * active = scheduler._worker[thread_id]._active.load();
-      bool result = active->pop();
-      if (auto array = active->reclaim())
+      Deque * deque = scheduler._worker[thread_id]._deque.load();
+      bool result = deque->pop();
+      if (auto garbage = deque->reclaim())
       {
-        scheduler._gc.retire(array);
+        scheduler._gc.retire(garbage);
       }
       return result;
     }
@@ -63,24 +63,23 @@ namespace typon
     {
       Scheduler & scheduler = get();
       Worker & worker = scheduler._worker[thread_id];
-      Deque * deque = worker._active.load();
-      worker._active.store(nullptr);
+      Deque * deque = worker._deque.load();
+      worker._deque.store(nullptr);
       deque->suspend(coroutine);
-      for (uint i = 0; i < scheduler._concurrency * 2; i++)
-      {
       uint id = fdt::random::random() % scheduler._concurrency;
-        if (scheduler._worker[id].try_add(deque))
-        {
-          return deque;
-        }
-      }
-      worker.add(deque);
+      scheduler._worker[id].add(deque);
       return deque;
     }
 
     static void enable(Deque * deque) noexcept
     {
-      deque->_resumable.store(true);
+      auto state = deque->_state.exchange(Deque::Resumable);
+      if (state == Deque::Empty)
+      {
+        Scheduler & scheduler = get();
+        uint id = fdt::random::random() % scheduler._concurrency;
+        scheduler._worker[id].add(deque);
+      }
       get()._notifyer.notify_one();
     }
 

rt/include/typon/core/worker.hpp

@@ -43,7 +43,7 @@ namespace typon
     };
 
     std::mutex _mutex;
-    std::atomic<Deque *> _active {nullptr};
+    std::atomic<Deque *> _deque {nullptr};
     std::vector<Deque *> _pool;
     fdt::lock_free::garbage_collector * _gc;
 
@@ -53,29 +53,29 @@ namespace typon
       {
         delete deque;
       }
-      if (auto active = _active.load())
+      if (auto deque = _deque.load())
       {
-        delete active;
+        delete deque;
       }
     }
 
     void resume(Work & work) noexcept
     {
-      auto active = _active.load();
+      auto deque = _deque.load();
       if (work._state == Work::Resumable)
       {
-        _active.store(work._deque);
-        if (active)
+        _deque.store(work._deque);
+        if (deque)
         {
-          _gc->retire(active);
+          _gc->retire(deque);
         }
         work._deque->resume();
       }
       else
       {
-        if (!active)
+        if (!deque)
         {
-          _active.store(new Deque());
+          _deque.store(new Deque());
         }
         work._task.resume();
       }
@@ -105,25 +105,32 @@ namespace typon
         return {};
       }
       std::lock_guard lock(_mutex, std::adopt_lock);
-      auto active = _active.load();
-      auto total = _pool.size() + bool(active);
+      auto deque = _deque.load();
+      auto total = _pool.size() + bool(deque);
       if (total == 0)
       {
         return {};
       }
-      auto index = fdt::random::random64() % (_pool.size() + bool(active));
+      auto index = fdt::random::random64() % total;
       if (index == _pool.size())
       {
-        if (auto task = active->steal())
+        if (auto task = deque->steal())
         {
           task.thefts()++;
           return task;
         }
         return {};
       }
-      auto deque = _pool[index];
-      if (!deque->_resumable.load())
+      deque = _pool[index];
+      if (deque->_state.load() == Deque::Resumable)
+      {
+        if (index < _pool.size() - 1)
         {
+          _pool[index] = _pool.back();
+        }
+        _pool.pop_back();
+        return deque;
+      }
       auto task = deque->pop_top();
       if (auto garbage = deque->reclaim())
       {
@@ -134,15 +141,18 @@ namespace typon
         task.thefts()++;
         return task;
       }
-        return {};
-      }
       if (index < _pool.size() - 1)
       {
         _pool[index] = _pool.back();
       }
       _pool.pop_back();
+      Deque::State expected = Deque::Suspended;
+      if (!deque->_state.compare_exchange_strong(expected, Deque::Empty))
+      {
         return deque;
       }
+      return {};
+    }
   };
 
 }