From a2be4d3ee5b81d056bf7b984f3afeca1be655185 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sat, 10 Mar 2018 17:33:14 -0800
Subject: [PATCH] ircd::ctx: Add when_any() / when_all().

---
 include/ircd/ctx/future.h | 60 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/include/ircd/ctx/future.h b/include/ircd/ctx/future.h
index c75f3dd1d..11d11c6c2 100644
--- a/include/ircd/ctx/future.h
+++ b/include/ircd/ctx/future.h
@@ -20,6 +20,8 @@ namespace ircd::ctx
 	template<class... T> struct scoped_future;
 	enum class future_status;
 
+	template<class it> future<it> when_any(it first, const it &last);
+	template<class it> future<void> when_all(it first, const it &last);
 }
 
 enum class ircd::ctx::future_status
@@ -359,3 +361,61 @@ ircd::ctx::wait_until(const future<T> &f,
 		future_status::ready:
 		future_status::deferred;
 }
+
+template<class it>
+ircd::ctx::future<void>
+ircd::ctx::when_all(it first,
+                    const it &last)
+{
+	promise<void> p;
+	future<void> ret(p);
+	for(; first != last; ++first)
+		if(pending(first->st))
+			first->st.then = [p](shared_state_base &) mutable
+			{
+				if(!p.valid())
+					return;
+
+				if(refcount(*p.st) < 2)
+					return p.set_value();
+
+				return remove(*p.st, p);
+			};
+
+	if(refcount(*p.st) <= 1)
+		p.set_value();
+
+	return ret;
+}
+
+template<class it>
+ircd::ctx::future<it>
+ircd::ctx::when_any(it first,
+                    const it &last)
+{
+	promise<it> p;
+	future<it> ret(p);
+	for(auto first_(first); first_ != last; ++first_)
+		if(ready(first_->st))
+		{
+			set_observed(first_->st);
+			p.set_value(first_);
+			return ret;
+		}
+
+	for(; first != last; ++first)
+		if(pending(first->st))
+			first->st.then = [p, first](shared_state_base &) mutable
+			{
+				if(!p.valid())
+					return;
+
+				set_observed(first->st);
+				p.set_value(first);
+			};
+
+	if(refcount(*p.st) <= 1)
+		p.set_value(first);
+
+	return ret;
+}