From 0924b63e10513f0bc8fb9d8cc77114d141c60877 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Wed, 17 Feb 2021 19:49:00 +0100
Subject: [PATCH] event/TimerWheel: add `empty` flag to optimize a common case
---
src/event/TimerWheel.cxx | 9 ++++++++-
src/event/TimerWheel.hxx | 10 ++++++++++
2 files changed, 18 insertions(+), 1 deletion(-)
diff --git a/src/event/TimerWheel.cxx b/src/event/TimerWheel.cxx
index f0d3dea4d..2f406a302 100644
--- a/src/event/TimerWheel.cxx
+++ b/src/event/TimerWheel.cxx
@@ -54,6 +54,8 @@ TimerWheel::Insert(CoarseTimerEvent &t) noexcept
const auto due = std::max(t.GetDue(), last_time);
buckets[BucketIndexAt(due)].push_back(t);
+
+ empty = false;
}
void
@@ -99,10 +101,15 @@ TimerWheel::GetNextDue(const std::size_t bucket_index,
inline Event::Duration
TimerWheel::GetSleep(Event::TimePoint now) const noexcept
{
+ if (empty)
+ return Event::Duration(-1);
+
auto t = GetNextDue(BucketIndexAt(now), GetBucketStartTime(now));
assert(t > now);
- if (t == Event::TimePoint::max())
+ if (t == Event::TimePoint::max()) {
+ empty = true;
return Event::Duration(-1);
+ }
return t - now;
}
diff --git a/src/event/TimerWheel.hxx b/src/event/TimerWheel.hxx
index 685829bd4..fd10ee9e4 100644
--- a/src/event/TimerWheel.hxx
+++ b/src/event/TimerWheel.hxx
@@ -72,6 +72,16 @@ class TimerWheel final {
*/
Event::TimePoint last_time{};
+ /**
+ * If this flag is true, then all buckets are guaranteed to be
+ * empty. If it is false, the buckets may or may not be
+ * empty; if so, the next full scan will set it back to true.
+ *
+ * This field is "mutable" so the "const" method GetSleep()
+ * can update it.
+ */
+ mutable bool empty = true;
+
public:
TimerWheel() noexcept;
~TimerWheel() noexcept;