From dcfae310abba972e1481d1257a311f41d6b3a7a7 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Thu, 16 Mar 2023 19:31:56 -0700
Subject: [PATCH] ircd::m::vm::notify: Add promise/future based notify
 interface.

---
 include/ircd/m/vm/notify.h | 15 +++++++++++++++
 matrix/vm_notify.cc        | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/include/ircd/m/vm/notify.h b/include/ircd/m/vm/notify.h
index e5d168f49..4b7bd099b 100644
--- a/include/ircd/m/vm/notify.h
+++ b/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
diff --git a/matrix/vm_notify.cc b/matrix/vm_notify.cc
index dc258ff05..843cd6553 100644
--- a/matrix/vm_notify.cc
+++ b/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 &)