unions parent/exception types

Author: Conor

src/core/frame.cxx

@@ -1,4 +1,5 @@
 module;
+#include "libfork/__impl/assume.hpp"
 #include "libfork/__impl/utils.hpp"
 export module libfork.core:frame;
 
@@ -16,7 +17,14 @@ export enum class category : std::uint8_t {
   fork,
 };
 
-struct cancellation {};
+struct cancellation {
+  cancellation *parent = nullptr;
+  std::atomic<std::uint32_t> cancelled = 0;
+};
+
+struct block_type {
+  //
+};
 
 // =================== Frame =================== //
 
@@ -27,7 +35,21 @@ struct frame_type {
   using allocator_type = allocator_t<Context>;
   using checkpoint_type = checkpoint_t<allocator_type>;
 
-  frame_type *parent;
+  union parent_union {
+    frame_type *frame;
+    block_type *block;
+  };
+
+  struct except_type {
+    parent_union stashed;
+    std::exception_ptr exception;
+  };
+
+  union {
+    parent_union parent;
+    except_type *except;
+  };
+
   cancellation *cancel;
 
   [[no_unique_address]]

src/core/promise.cxx

@@ -61,13 +61,18 @@ template <worker_context Context>
 [[nodiscard]]
 constexpr auto final_suspend(frame_type<Context> *frame) noexcept -> coro<> {
 
+  // Validate final state
+  LF_ASSUME(frame->steals == 0);
+  LF_ASSUME(frame->joins == k_u16_max);
+  LF_ASSUME(frame->exception_bit == 0);
+
   defer _ = [frame] noexcept -> void {
     frame->handle().destroy();
   };
 
   switch (not_null(frame)->kind) {
     case category::call:
-      return not_null(frame->parent)->handle();
+      return not_null(frame->parent.frame)->handle();
     case category::root:
       // TODO: root handling
       return std::noop_coroutine();
@@ -79,7 +84,7 @@ constexpr auto final_suspend(frame_type<Context> *frame) noexcept -> coro<> {
 
   Context *context = not_null(thread_context<Context>);
 
-  frame_type<Context> *parent = not_null(frame->parent);
+  frame_type<Context> *parent = not_null(frame->parent.frame);
 
   if (frame_handle last_pushed = context->pop()) {
     // No-one stole continuation, we are the exclusive owner of parent, so we
@@ -186,7 +191,7 @@ struct awaitable : std::suspend_always {
     // TODO: handle cancellation
 
     // Propagate parent->child relationships
-    self.child->parent = &parent.promise().frame;
+    self.child->parent.frame = &parent.promise().frame;
     self.child->cancel = parent.promise().frame.cancel;
     self.child->stack_ckpt = not_null(thread_context<Context>)->alloc().checkpoint();
     self.child->kind = Cat;