From 7d502fb448be74919aedb2ef895cc0f656898871 Mon Sep 17 00:00:00 2001
From: Max Kellermann <mk@cm4all.com>
Date: Tue, 5 Mar 2019 22:06:09 +0100
Subject: [PATCH] event/Loop: round epoll_wait() timeout up

This implements proper rounding, amending commit dcbb9fe07ce
---
 src/event/Loop.cxx | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/event/Loop.cxx b/src/event/Loop.cxx
index a5475c3fb..6631c41c7 100644
--- a/src/event/Loop.cxx
+++ b/src/event/Loop.cxx
@@ -162,6 +162,18 @@ EventLoop::HandleTimers() noexcept
 	return Event::Duration(-1);
 }
 
+template<class ToDuration, class Rep, class Period>
+static constexpr ToDuration
+duration_cast_round_up(std::chrono::duration<Rep, Period> d) noexcept
+{
+	using FromDuration = decltype(d);
+	constexpr auto one = std::chrono::duration_cast<FromDuration>(ToDuration(1));
+	constexpr auto round_add = one > one.zero()
+		? one - FromDuration(1)
+		: one.zero();
+	return std::chrono::duration_cast<ToDuration>(d + round_add);
+}
+
 /**
  * Convert the given timeout specification to a milliseconds integer,
  * to be used by functions like poll() and epoll_wait().  Any negative
@@ -171,8 +183,7 @@ static constexpr int
 ExportTimeoutMS(Event::Duration timeout)
 {
 	return timeout >= timeout.zero()
-		/* round up (+1) to avoid unnecessary wakeups */
-		? int(std::chrono::duration_cast<std::chrono::milliseconds>(timeout).count()) + 1
+		? int(duration_cast_round_up<std::chrono::milliseconds>(timeout).count())
 		: -1;
 }