diff --git a/include/ircd/ctx/future.h b/include/ircd/ctx/future.h
index 42ad58832..ebed419a7 100644
--- a/include/ircd/ctx/future.h
+++ b/include/ircd/ctx/future.h
@@ -58,6 +58,8 @@ class ircd::ctx::future
 	T get();
 	operator T()                                 { return get();                                   }
 
+	void then(decltype(shared_state<T>::callback));
+
 	future();
 	future(promise<T> &promise);
 };
@@ -82,6 +84,8 @@ class ircd::ctx::future<void>
 	template<class duration> future_status wait(const duration &d) const;
 	void wait() const;
 
+	void then(decltype(shared_state<void>::callback));
+
 	future();
 	future(promise<void> &promise);
 };
@@ -136,6 +140,21 @@ ircd::ctx::future<T>::future(promise<T> &promise)
 {
 }
 
+template<class T>
+void
+ircd::ctx::future<T>::then(decltype(shared_state<T>::callback) cb)
+{
+	assert(valid());
+	st->callback = std::move(cb);
+}
+
+inline void
+ircd::ctx::future<void>::then(decltype(shared_state<void>::callback) cb)
+{
+	assert(valid());
+	st->callback = std::move(cb);
+}
+
 template<class T>
 T
 ircd::ctx::future<T>::get()
diff --git a/include/ircd/ctx/promise.h b/include/ircd/ctx/promise.h
index c38ddb2fd..74f8e5c59 100644
--- a/include/ircd/ctx/promise.h
+++ b/include/ircd/ctx/promise.h
@@ -147,6 +147,10 @@ ircd::ctx::promise<T>::set_value(T&& val)
 	st->val = std::move(val);
 	st->finished = true;
 	st->cond.notify_all();
+	if(st->callback) ircd::post([st(st)]
+	{
+		st->callback(st->eptr, st->val);
+	});
 }
 
 inline void
@@ -156,6 +160,10 @@ ircd::ctx::promise<void>::set_value()
 	assert(!finished());
 	st->finished = true;
 	st->cond.notify_all();
+	if(st->callback) ircd::post([st(st)]
+	{
+		st->callback(st->eptr);
+	});
 }
 
 template<class T>
@@ -167,6 +175,10 @@ ircd::ctx::promise<T>::set_value(const T &val)
 	st->val = val;
 	st->finished = true;
 	st->cond.notify_all();
+	if(st->callback) ircd::post([st(st)]
+	{
+		st->callback(st->eptr, st->val);
+	});
 }
 
 inline void
@@ -177,6 +189,10 @@ ircd::ctx::promise<void>::set_exception(std::exception_ptr eptr)
 	st->eptr = std::move(eptr);
 	st->finished = true;
 	st->cond.notify_all();
+	if(st->callback) ircd::post([st(st)]
+	{
+		st->callback(st->eptr);
+	});
 }
 
 template<class T>
@@ -188,4 +204,8 @@ ircd::ctx::promise<T>::set_exception(std::exception_ptr eptr)
 	st->eptr = std::move(eptr);
 	st->finished = true;
 	st->cond.notify_all();
+	if(st->callback) ircd::post([st(st)]
+	{
+		st->callback(st->eptr, st->val);
+	});
 }
diff --git a/include/ircd/ctx/shared_state.h b/include/ircd/ctx/shared_state.h
index e9d422777..58d751cf8 100644
--- a/include/ircd/ctx/shared_state.h
+++ b/include/ircd/ctx/shared_state.h
@@ -36,6 +36,7 @@ struct ircd::ctx::shared_state
 	using reference_type  = T &;
 
 	T val;
+	std::function<void (std::exception_ptr, T) noexcept> callback;
 
 	std::shared_ptr<const shared_state<T>> share() const;
 	std::shared_ptr<shared_state<T>> share();
@@ -48,6 +49,8 @@ struct ircd::ctx::shared_state<void>
 {
 	using value_type      = void;
 
+	std::function<void (std::exception_ptr) noexcept> callback;
+
 	std::shared_ptr<const shared_state<void>> share() const;
 	std::shared_ptr<shared_state<void>> share();
 };