Enable opt-in deferred reclamation of forks

rt/include/typon/fork.hpp

@@ -63,14 +63,18 @@ namespace typon
             {
               return span->_coroutine;
             }
+            auto rank = coroutine.promise()._rank;
             if (auto & exception = coroutine.promise()._exception)
             {
-              span->set_exception(exception, coroutine.promise()._rank);
+              span->set_exception(exception, rank);
             }
-            auto & ref = coroutine.promise()._node._ref;
-            if (!ref.exchange(false, std::memory_order_acq_rel))
+            if (!(rank & 1))
             {
-              coroutine.destroy();
+              auto & ref = coroutine.promise()._node._ref;
+              if (!ref.exchange(false, std::memory_order_acq_rel))
+              {
+                coroutine.destroy();
+              }
             }
             u64 n = span->_n.fetch_sub(1, std::memory_order_acq_rel);
             if (n == 1)
@@ -85,25 +89,45 @@ namespace typon
       }
     };
 
-    struct awaitable
+    struct awaitable : std::suspend_always
     {
       std::coroutine_handle<promise_type> _coroutine;
 
-      awaitable(std::coroutine_handle<promise_type> coroutine) noexcept
-        : _coroutine(coroutine)
-      {}
+      template <typename Promise>
+      auto await_suspend(std::coroutine_handle<Promise> continuation) noexcept
+      {
+        Span * span = &(continuation.promise()._span);
+        _coroutine.promise()._span = span;
+        _coroutine.promise()._rank = (span->_thefts << 1);
 
-      bool await_ready() noexcept
+        std::coroutine_handle<> on_stack_handle = _coroutine;
+        Scheduler::push(span);
+        return on_stack_handle;
+      }
+
+      auto await_resume()
       {
-        return false;
+        auto thefts = _coroutine.promise()._span->_thefts;
+        auto rank = _coroutine.promise()._rank;
+        return Forked<T>(_coroutine, (thefts == (rank >> 1)), true);
       }
+    };
+
+    auto operator co_await() &&
+    {
+      return awaitable { {}, _coroutine };
+    }
+
+    struct noloop_awaitable : std::suspend_always
+    {
+      std::coroutine_handle<promise_type> _coroutine;
 
       template <typename Promise>
       auto await_suspend(std::coroutine_handle<Promise> continuation) noexcept
       {
         Span * span = &(continuation.promise()._span);
         _coroutine.promise()._span = span;
-        _coroutine.promise()._rank = span->_thefts;
+        _coroutine.promise()._rank = (span->_thefts << 1) + 1;
 
         std::coroutine_handle<> on_stack_handle = _coroutine;
         Scheduler::push(span);
@@ -114,13 +138,18 @@ namespace typon
       {
         auto thefts = _coroutine.promise()._span->_thefts;
         auto rank = _coroutine.promise()._rank;
-        return Forked<T>(_coroutine, (thefts == rank));
+        bool ready = thefts == (rank >> 1);
+        if (!ready)
+        {
+          _coroutine.promise()._span->_children.push_back(_coroutine);
+        }
+        return Forked<T>(_coroutine, ready, false);
       }
     };
 
-    auto operator co_await() &&
+    auto noloop() &&
     {
-      return awaitable { _coroutine };
+      return noloop_awaitable { {}, _coroutine };
     }
   };
 

rt/include/typon/forked.hpp

@@ -111,7 +111,7 @@ namespace typon
     Result<T> * _result = nullptr;
 
     template <typename Promise>
-    Forked(std::coroutine_handle<Promise> coroutine, bool ready)
+    Forked(std::coroutine_handle<Promise> coroutine, bool ready, bool owning)
     {
       if (ready)
       {
@@ -120,7 +120,7 @@ namespace typon
       }
       else
       {
-        this->_node = &(coroutine.promise()._node);
+        this->_node = owning ? &(coroutine.promise()._node) : nullptr;
         _result = &(coroutine.promise());
       }
     }
@@ -197,11 +197,11 @@ namespace typon
     ForkNode * _node;
 
     template <typename Promise>
-    Forked(std::coroutine_handle<Promise> coroutine, bool ready)
+    Forked(std::coroutine_handle<Promise> coroutine, bool ready, bool owning)
     {
       _ready = ready;
       _result = &(coroutine.promise());
-      _node = &(coroutine.promise()._node);
+      _node = (owning | ready) ? &(coroutine.promise()._node) : nullptr;
       if (ready)
       {
         if (auto & exception = coroutine.promise()._exception)

rt/include/typon/span.hpp

@@ -7,6 +7,7 @@
 #include <cstdint>
 #include <exception>
 #include <limits>
+#include <vector>
 
 #include <typon/defer.hpp>
 #include <typon/theft_point.hpp>
@@ -31,6 +32,8 @@ namespace typon
 
     std::atomic<Error *> _error { nullptr };
 
+    std::vector<std::coroutine_handle<>> _children;
+
     std::atomic<u64> _n = UMAX;
 
     Span(std::coroutine_handle<> coroutine) noexcept
@@ -43,6 +46,16 @@ namespace typon
       {
         delete error;
       }
+      clear_children();
+    }
+
+    void clear_children() noexcept
+    {
+      for (auto & child : _children)
+      {
+        child.destroy();
+      }
+      _children.clear();
     }
 
     void check_exception()