Merge tag 'v0.21.18'

release v0.21.18

src/event/Loop.cxx

@@ -137,7 +137,8 @@ static constexpr int
 ExportTimeoutMS(std::chrono::steady_clock::duration timeout)
 {
 	return timeout >= timeout.zero()
-		? int(std::chrono::duration_cast<std::chrono::milliseconds>(timeout).count())
+		/* round up (+1) to avoid unnecessary wakeups */
+		? int(std::chrono::duration_cast<std::chrono::milliseconds>(timeout).count()) + 1
 		: -1;
 }
 
@@ -220,7 +221,6 @@ EventLoop::Run() noexcept
 	} while (!quit);
 
 #ifndef NDEBUG
-	assert(busy);
 	assert(thread.IsInside());
 #endif
 }

src/event/MultiSocketMonitor.cxx

@@ -22,6 +22,10 @@
 
 #include <algorithm>
 
+#ifdef USE_EPOLL
+#include <errno.h>
+#endif
+
 #ifndef _WIN32
 #include <poll.h>
 #endif
@@ -37,17 +41,42 @@ MultiSocketMonitor::Reset() noexcept
 	assert(GetEventLoop().IsInside());
 
 	fds.clear();
+#ifdef USE_EPOLL
+	always_ready_fds.clear();
+#endif
 	IdleMonitor::Cancel();
 	timeout_event.Cancel();
 	ready = refresh = false;
 }
 
+bool
+MultiSocketMonitor::AddSocket(SocketDescriptor fd, unsigned events) noexcept
+{
+	fds.emplace_front(*this, fd);
+	bool success = fds.front().Schedule(events);
+	if (!success) {
+		fds.pop_front();
+
+#ifdef USE_EPOLL
+		if (errno == EPERM)
+			/* not supported by epoll (e.g. "/dev/null"):
+			   add it to the "always ready" list */
+			always_ready_fds.push_front({fd, events});
+#endif
+	}
+
+	return success;
+}
+
 void
 MultiSocketMonitor::ClearSocketList() noexcept
 {
 	assert(GetEventLoop().IsInside());
 
 	fds.clear();
+#ifdef USE_EPOLL
+	always_ready_fds.clear();
+#endif
 }
 
 #ifndef _WIN32
@@ -55,6 +84,10 @@ MultiSocketMonitor::ClearSocketList() noexcept
 void
 MultiSocketMonitor::ReplaceSocketList(pollfd *pfds, unsigned n) noexcept
 {
+#ifdef USE_EPOLL
+	always_ready_fds.clear();
+#endif
+
 	pollfd *const end = pfds + n;
 
 	UpdateSocketList([pfds, end](SocketDescriptor fd) -> unsigned {
@@ -64,9 +97,7 @@ MultiSocketMonitor::ReplaceSocketList(pollfd *pfds, unsigned n) noexcept
 			if (i == end)
 				return 0;
 
-			auto events = i->events;
-			i->events = 0;
-			return events;
+			return std::exchange(i->events, 0);
 		});
 
 	for (auto i = pfds; i != end; ++i)
@@ -79,7 +110,20 @@ MultiSocketMonitor::ReplaceSocketList(pollfd *pfds, unsigned n) noexcept
 void
 MultiSocketMonitor::Prepare() noexcept
 {
-	const auto timeout = PrepareSockets();
+	auto timeout = PrepareSockets();
+
+#ifdef USE_EPOLL
+	if (!always_ready_fds.empty()) {
+		/* if there was at least one file descriptor not
+		   supported by epoll, install a very short timeout
+		   because we assume it's always ready */
+		constexpr std::chrono::steady_clock::duration ready_timeout =
+			std::chrono::milliseconds(1);
+		if (timeout < timeout.zero() || timeout > ready_timeout)
+			timeout = ready_timeout;
+	}
+#endif
+
 	if (timeout >= timeout.zero())
 		timeout_event.Schedule(timeout);
 	else

src/event/MultiSocketMonitor.hxx

@@ -49,12 +49,10 @@ class MultiSocketMonitor : IdleMonitor
 		unsigned revents;
 
 	public:
-		SingleFD(MultiSocketMonitor &_multi, SocketDescriptor _fd,
-			 unsigned events) noexcept
+		SingleFD(MultiSocketMonitor &_multi,
+			 SocketDescriptor _fd) noexcept
 			:SocketMonitor(_fd, _multi.GetEventLoop()),
-			multi(_multi), revents(0) {
-			Schedule(events);
-		}
+			multi(_multi), revents(0) {}
 
 		SocketDescriptor GetSocket() const noexcept {
 			return SocketMonitor::GetSocket();
@@ -85,8 +83,6 @@ class MultiSocketMonitor : IdleMonitor
 		}
 	};
 
-	friend class SingleFD;
-
 	TimerEvent timeout_event;
 
 	/**
@@ -105,6 +101,21 @@ class MultiSocketMonitor : IdleMonitor
 
 	std::forward_list<SingleFD> fds;
 
+#ifdef USE_EPOLL
+	struct AlwaysReady {
+		const SocketDescriptor fd;
+		const unsigned revents;
+	};
+
+	/**
+	 * A list of file descriptors which are always ready.  This is
+	 * a kludge needed because the ALSA output plugin gives us a
+	 * file descriptor to /dev/null, which is incompatible with
+	 * epoll (epoll_ctl() returns -EPERM).
+	 */
+	std::forward_list<AlwaysReady> always_ready_fds;
+#endif
+
 public:
 	static constexpr unsigned READ = SocketMonitor::READ;
 	static constexpr unsigned WRITE = SocketMonitor::WRITE;
@@ -146,9 +157,7 @@ public:
 	 *
 	 * May only be called from PrepareSockets().
 	 */
-	void AddSocket(SocketDescriptor fd, unsigned events) noexcept {
-		fds.emplace_front(*this, fd, events);
-	}
+	bool AddSocket(SocketDescriptor fd, unsigned events) noexcept;
 
 	/**
 	 * Remove all sockets.
@@ -203,6 +212,11 @@ public:
 				i.ClearReturnedEvents();
 			}
 		}
+
+#ifdef USE_EPOLL
+		for (const auto &i : always_ready_fds)
+			f(i.fd, i.revents);
+#endif
 	}
 
 protected:
@@ -231,7 +245,6 @@ private:
 
 	void OnTimeout() noexcept {
 		SetReady();
-		IdleMonitor::Schedule();
 	}
 
 	virtual void OnIdle() noexcept final;

src/event/SocketMonitor.cxx

@@ -64,20 +64,24 @@ SocketMonitor::Close() noexcept
 	Steal().Close();
 }
 
-void
+bool
 SocketMonitor::Schedule(unsigned flags) noexcept
 {
 	assert(IsDefined());
 
 	if (flags == GetScheduledFlags())
-		return;
+		return true;
 
+	bool success;
 	if (scheduled_flags == 0)
-		loop.AddFD(fd.Get(), flags, *this);
+		success = loop.AddFD(fd.Get(), flags, *this);
 	else if (flags == 0)
-		loop.RemoveFD(fd.Get(), *this);
+		success = loop.RemoveFD(fd.Get(), *this);
 	else
-		loop.ModifyFD(fd.Get(), flags, *this);
+		success = loop.ModifyFD(fd.Get(), flags, *this);
 
-	scheduled_flags = flags;
+	if (success)
+		scheduled_flags = flags;
+
+	return success;
 }

src/event/SocketMonitor.hxx

@@ -98,18 +98,22 @@ public:
 		return scheduled_flags;
 	}
 
-	void Schedule(unsigned flags) noexcept;
+	/**
+	 * @return true on success, false on error (with errno set if
+	 * USE_EPOLL is defined)
+	 */
+	bool Schedule(unsigned flags) noexcept;
 
 	void Cancel() noexcept {
 		Schedule(0);
 	}
 
-	void ScheduleRead() noexcept {
-		Schedule(GetScheduledFlags() | READ | HANGUP | ERROR);
+	bool ScheduleRead() noexcept {
+		return Schedule(GetScheduledFlags() | READ | HANGUP | ERROR);
 	}
 
-	void ScheduleWrite() noexcept {
-		Schedule(GetScheduledFlags() | WRITE);
+	bool ScheduleWrite() noexcept {
+		return Schedule(GetScheduledFlags() | WRITE);
 	}
 
 	void CancelRead() noexcept {