event/SignalMonitor: use signalfd() if available

Makefile.am

@@ -288,6 +288,7 @@ libsystem_a_SOURCES = \
 	src/system/SocketUtil.cxx src/system/SocketUtil.hxx \
 	src/system/SocketError.hxx \
 	src/system/resolver.c src/system/resolver.h \
+	src/system/SignalFD.cxx src/system/SignalFD.hxx \
 	src/system/clock.c src/system/clock.h
 
 # Event loop library

configure.ac

@@ -141,6 +141,7 @@ AC_SEARCH_LIBS([gethostbyname], [nsl])
 
 AC_CHECK_FUNCS(pipe2 accept4)
 MPD_OPTIONAL_FUNC(eventfd, USE_EVENTFD)
+MPD_OPTIONAL_FUNC(signalfd, USE_SIGNALFD)
 
 AC_SEARCH_LIBS([exp], [m],,
 	[AC_MSG_ERROR([exp() not found])])

src/event/SignalMonitor.cxx

@@ -27,27 +27,58 @@
 #include "util/Manual.hxx"
 #include "system/FatalError.hxx"
 
+#ifdef USE_SIGNALFD
+#include "system/SignalFD.hxx"
+#else
+#include "WakeFD.hxx"
+#endif
+
+#ifndef USE_SIGNALFD
 #include <atomic>
+#endif
+
 #include <algorithm>
 
 class SignalMonitor final : private SocketMonitor {
+#ifdef USE_SIGNALFD
+	SignalFD fd;
+#else
 	WakeFD fd;
+#endif
 
 public:
 	SignalMonitor(EventLoop &_loop)
 		:SocketMonitor(_loop) {
+#ifndef USE_SIGNALFD
 		SocketMonitor::Open(fd.Get());
 		SocketMonitor::ScheduleRead();
+#endif
 	}
 
 	~SignalMonitor() {
 		/* prevent the descriptor to be closed twice */
-		SocketMonitor::Steal();
+#ifdef USE_SIGNALFD
+		if (SocketMonitor::IsDefined())
+#endif
+			SocketMonitor::Steal();
 	}
 
+#ifdef USE_SIGNALFD
+	void Update(sigset_t &mask) {
+		const bool was_open = SocketMonitor::IsDefined();
+
+		fd.Create(mask);
+
+		if (!was_open) {
+			SocketMonitor::Open(fd.Get());
+			SocketMonitor::ScheduleRead();
+		}
+	}
+#else
 	void WakeUp() {
 		fd.Write();
 	}
+#endif
 
 private:
 	virtual bool OnSocketReady(unsigned flags) override;
@@ -57,10 +88,16 @@ private:
 static constexpr unsigned MAX_SIGNAL = 64;
 
 static SignalHandler signal_handlers[MAX_SIGNAL];
+
+#ifdef USE_SIGNALFD
+static sigset_t signal_mask;
+#else
 static std::atomic_bool signal_pending[MAX_SIGNAL];
+#endif
 
 static Manual<SignalMonitor> monitor;
 
+#ifndef USE_SIGNALFD
 static void
 SignalCallback(int signo)
 {
@@ -69,13 +106,20 @@ SignalCallback(int signo)
 	if (!signal_pending[signo].exchange(true))
 		monitor->WakeUp();
 }
+#endif
 
 void
 SignalMonitorInit(EventLoop &loop)
 {
+#ifdef USE_SIGNALFD
+	sigemptyset(&signal_mask);
+#endif
+
 	monitor.Construct(loop);
 }
 
+#ifndef USE_SIGNALFD
+
 static void
 x_sigaction(int signum, const struct sigaction &act)
 {
@@ -83,9 +127,14 @@ x_sigaction(int signum, const struct sigaction &act)
 		FatalSystemError("sigaction() failed");
 }
 
+#endif
+
 void
 SignalMonitorFinish()
 {
+#ifdef USE_SIGNALFD
+	std::fill_n(signal_handlers, MAX_SIGNAL, nullptr);
+#else
 	struct sigaction sa;
 	sa.sa_flags = 0;
 	sigemptyset(&sa.sa_mask);
@@ -99,6 +148,7 @@ SignalMonitorFinish()
 	}
 
 	std::fill_n(signal_pending, MAX_SIGNAL, false);
+#endif
 
 	monitor.Destruct();
 }
@@ -107,25 +157,46 @@ void
 SignalMonitorRegister(int signo, SignalHandler handler)
 {
 	assert(signal_handlers[signo] == nullptr);
+#ifndef USE_SIGNALFD
 	assert(!signal_pending[signo]);
+#endif
 
 	signal_handlers[signo] = handler;
 
+#ifdef USE_SIGNALFD
+	sigaddset(&signal_mask, signo);
+
+	if (sigprocmask(SIG_BLOCK, &signal_mask, nullptr) < 0)
+		FatalSystemError("sigprocmask() failed");
+
+	monitor->Update(signal_mask);
+#else
 	struct sigaction sa;
 	sa.sa_flags = 0;
 	sigemptyset(&sa.sa_mask);
 	sa.sa_handler = SignalCallback;
 	x_sigaction(signo, sa);
+#endif
 }
 
 bool
 SignalMonitor::OnSocketReady(unsigned)
 {
+#ifdef USE_SIGNALFD
+	int signo;
+	while ((signo = fd.Read()) >= 0) {
+		assert(unsigned(signo) < MAX_SIGNAL);
+		assert(signal_handlers[signo] != nullptr);
+
+		signal_handlers[signo]();
+	}
+#else
 	fd.Read();
 
 	for (unsigned i = 0; i < MAX_SIGNAL; ++i)
 		if (signal_pending[i].exchange(false))
 			signal_handlers[i]();
+#endif
 
 	return true;
 }

src/system/SignalFD.cxx

+/*
+ * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#ifdef USE_SIGNALFD
+#include "SignalFD.hxx"
+#include "fd_util.h"
+#include "FatalError.hxx"
+
+#include <assert.h>
+#include <unistd.h>
+#include <sys/signalfd.h>
+
+void
+SignalFD::Create(const sigset_t &mask)
+{
+	fd = ::signalfd(fd, &mask, SFD_NONBLOCK|SFD_CLOEXEC);
+	if (fd < 0)
+		FatalSystemError("signalfd() failed");
+}
+
+void
+SignalFD::Close()
+{
+	if (fd >= 0) {
+		::close(fd);
+		fd = -1;
+	}
+}
+
+int
+SignalFD::Read()
+{
+	assert(fd >= 0);
+
+	signalfd_siginfo info;
+	return read(fd, &info, sizeof(info)) > 0
+		? info.ssi_signo
+		: -1;
+}
+
+#endif /* USE_SIGNALFD */

src/system/SignalFD.hxx

+/*
+ * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_SIGNAL_FD_HXX
+#define MPD_SIGNAL_FD_HXX
+
+#include "check.h"
+
+#include <signal.h>
+
+/**
+ * A class that wraps signalfd().
+ */
+class SignalFD {
+	int fd;
+
+public:
+	SignalFD():fd(-1) {}
+	~SignalFD() {
+		Close();
+	}
+
+	SignalFD(const SignalFD &other) = delete;
+	SignalFD &operator=(const SignalFD &other) = delete;
+
+	/**
+	 * Create the signalfd or update its mask.
+	 *
+	 * All errors are fatal.
+	 */
+	void Create(const sigset_t &mask);
+	void Close();
+
+	int Get() const {
+		return fd;
+	}
+
+	/**
+	 * Read the next signal from the file descriptor.  Returns the
+	 * signal number on success or -1 if there are no more
+	 * signals.
+	 */
+	int Read();
+};
+
+#endif