ircd:Ⓜ️:vm::notify: Add promise/future based notify interface.

include/ircd/m/vm/notify.h

@@ -13,6 +13,8 @@
 
 namespace ircd::m::vm::notify
 {
+	struct future;
+
 	using value_type = std::pair<const event::id, ctx::promise<> *>;
 	using alloc_type = allocator::node<value_type>;
 	using map_type = std::multimap<const event::id, ctx::promise<> *, std::less<>, alloc_type::allocator>;
@@ -24,6 +26,19 @@ namespace ircd::m::vm::notify
 	bool wait(const event::id &, const milliseconds);
 }
 
+class ircd::m::vm::notify::future
+:public ctx::future<>
+{
+	node_type node;
+	ctx::promise<> promise;
+	unique_iterator<map_type> it;
+
+  public:
+	future(const event::id &);
+	future(future &&) = delete;
+	future(const future &) = delete;
+};
+
 /// Yields ctx until event was successfully evaluated. Returns false if
 /// timeout occurred.
 inline bool

matrix/vm_notify.cc

@@ -112,6 +112,44 @@ ircd::m::vm::notify::wait(const vector_view<const event::id> &event_id,
 	return exists;
 }
 
+//
+// future::future
+//
+
+ircd::m::vm::notify::future::future(const event::id &event_id)
+:ctx::future<>{ctx::already}
+{
+	if(m::exists(event_id))
+		return;
+
+	const auto &s
+	{
+		map.get_allocator().s
+	};
+
+	assert(s);
+	assert(!s->next);
+	const scope_restore next
+	{
+		s->next, reinterpret_cast<notify::value_type *>(&node)
+	};
+
+	it =
+	{
+		map, map.emplace(event_id, &promise)
+	};
+
+	assert(it->second);
+	static_cast<ctx::future<> &>(*this) = ctx::future<>
+	{
+		*it->second
+	};
+}
+
+//
+// internal
+//
+
 void
 ircd::m::vm::notify::hook_handle(const m::event &event,
                                  vm::eval &)