event/Loop: use ClockCache

src/event/Loop.cxx

@@ -159,7 +159,7 @@ EventLoop::AddTimer(TimerEvent &t, Event::Duration d) noexcept
 {
 	assert(IsInside());
 
-	t.due = now + d;
+	t.due = SteadyNow() + d;
 	timers.insert(t);
 	again = true;
 }
@@ -167,6 +167,8 @@ EventLoop::AddTimer(TimerEvent &t, Event::Duration d) noexcept
 inline Event::Duration
 EventLoop::HandleTimers() noexcept
 {
+	const auto now = SteadyNow();
+
 	Event::Duration timeout;
 
 	while (!quit) {
@@ -301,8 +303,9 @@ EventLoop::Run() noexcept
 	};
 #endif
 
+	steady_clock_cache.flush();
+
 	do {
-		now = std::chrono::steady_clock::now();
 		again = false;
 
 		/* invoke timers */
@@ -340,7 +343,7 @@ EventLoop::Run() noexcept
 
 		Wait(timeout);
 
-		now = std::chrono::steady_clock::now();
+		steady_clock_cache.flush();
 
 #ifdef HAVE_THREADED_EVENT_LOOP
 		{

src/event/Loop.hxx

@@ -24,6 +24,7 @@
 #include "Backend.hxx"
 #include "SocketEvent.hxx"
 #include "event/Features.h"
+#include "time/ClockCache.hxx"
 #include "util/Compiler.h"
 #include "util/IntrusiveList.hxx"
 
@@ -114,8 +115,6 @@ class EventLoop final
 	std::unique_ptr<Uring::Manager> uring;
 #endif
 
-	Event::Clock::time_point now = Event::Clock::now();
-
 #ifdef HAVE_THREADED_EVENT_LOOP
 	/**
 	 * A reference to the thread that is currently inside Run().
@@ -155,6 +154,8 @@ class EventLoop final
 
 	EventPollBackend poll_backend;
 
+	ClockCache<std::chrono::steady_clock> steady_clock_cache;
+
 public:
 	/**
 	 * Throws on error.
@@ -172,15 +173,23 @@ public:
 	EventLoop(const EventLoop &other) = delete;
 	EventLoop &operator=(const EventLoop &other) = delete;
 
+	const auto &GetSteadyClockCache() const noexcept {
+		return steady_clock_cache;
+	}
+
 	/**
-	 * A caching wrapper for Event::Clock::now().
+	 * Caching wrapper for std::chrono::steady_clock::now().  The
+	 * real clock is queried at most once per event loop
+	 * iteration, because it is assumed that the event loop runs
+	 * for a negligible duration.
 	 */
-	auto GetTime() const {
+	gcc_pure
+	const auto &SteadyNow() const noexcept {
 #ifdef HAVE_THREADED_EVENT_LOOP
 		assert(IsInside());
 #endif
 
-		return now;
+		return steady_clock_cache.now();
 	}
 
 #ifdef HAVE_URING