event/Loop: integrate io_uring support

src/event/Loop.cxx

@@ -23,6 +23,12 @@
 #include "DeferEvent.hxx"
 #include "util/ScopeExit.hxx"
 
+#ifdef HAVE_URING
+#include "UringManager.hxx"
+#include "util/PrintException.hxx"
+#include <stdio.h>
+#endif
+
 EventLoop::EventLoop(ThreadId _thread)
 	:SocketMonitor(*this),
 	 /* if this instance is hosted by an EventThread (no ThreadId
@@ -43,6 +49,25 @@ EventLoop::~EventLoop() noexcept
 	assert(timers.empty());
 }
 
+#ifdef HAVE_URING
+
+Uring::Queue *
+EventLoop::GetUring() noexcept
+{
+	if (!uring_initialized) {
+		try {
+			uring = std::make_unique<Uring::Manager>(*this);
+		} catch (...) {
+			fprintf(stderr, "Failed to initialize io_uring: ");
+			PrintException(std::current_exception());
+		}
+	}
+
+	return uring.get();
+}
+
+#endif
+
 void
 EventLoop::Break() noexcept
 {
@@ -155,6 +180,15 @@ EventLoop::Run() noexcept
 
 	SocketMonitor::Schedule(SocketMonitor::READ);
 	AtScopeExit(this) {
+#ifdef HAVE_URING
+		/* make sure that the Uring::Manager gets destructed
+		   from within the EventThread, or else its
+		   destruction in another thread will cause assertion
+		   failures */
+		uring.reset();
+		uring_initialized = false;
+#endif
+
 		SocketMonitor::Cancel();
 	};
 

src/event/Loop.hxx

@@ -38,6 +38,12 @@
 #include <cassert>
 #include <chrono>
 
+#include "io/uring/Features.h"
+#ifdef HAVE_URING
+#include <memory>
+namespace Uring { class Queue; class Manager; }
+#endif
+
 /**
  * An event loop that polls for events on file/socket descriptors.
  *
@@ -82,6 +88,10 @@ class EventLoop final : SocketMonitor
 				       boost::intrusive::constant_time_size<false>> DeferredList;
 	DeferredList deferred;
 
+#ifdef HAVE_URING
+	std::unique_ptr<Uring::Manager> uring;
+#endif
+
 	std::chrono::steady_clock::time_point now = std::chrono::steady_clock::now();
 
 	/**
@@ -108,6 +118,10 @@ class EventLoop final : SocketMonitor
 	 */
 	bool busy = true;
 
+#ifdef HAVE_URING
+	bool uring_initialized = false;
+#endif
+
 	PollGroup poll_group;
 	PollResult poll_result;
 
@@ -135,6 +149,11 @@ public:
 		return now;
 	}
 
+#ifdef HAVE_URING
+	gcc_pure
+	Uring::Queue *GetUring() noexcept;
+#endif
+
 	/**
 	 * Stop execution of this #EventLoop at the next chance.  This
 	 * method is thread-safe and non-blocking: after returning, it

src/event/UringManager.cxx

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2003-2020 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 "UringManager.hxx"
+#include "util/PrintException.hxx"
+
+namespace Uring {
+
+bool
+Manager::OnSocketReady(unsigned) noexcept
+{
+	try {
+		DispatchCompletions();
+		return true;
+	} catch (...) {
+		PrintException(std::current_exception());
+		return false;
+	}
+}
+
+void
+Manager::OnIdle() noexcept
+{
+	try {
+		Submit();
+	} catch (...) {
+		PrintException(std::current_exception());
+	}
+}
+
+} // namespace Uring

src/event/UringManager.hxx

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2003-2020 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.
+ */
+
+#pragma once
+
+#include "SocketMonitor.hxx"
+#include "IdleMonitor.hxx"
+#include "io/uring/Queue.hxx"
+
+namespace Uring {
+
+class Manager final : public Queue, SocketMonitor, IdleMonitor {
+public:
+	explicit Manager(EventLoop &event_loop)
+		:Queue(1024, 0),
+		 SocketMonitor(SocketDescriptor::FromFileDescriptor(GetFileDescriptor()),
+			       event_loop),
+		 IdleMonitor(event_loop)
+	{
+		SocketMonitor::ScheduleRead();
+	}
+
+	void Push(struct io_uring_sqe &sqe,
+		  Operation &operation) noexcept override {
+		AddPending(sqe, operation);
+		IdleMonitor::Schedule();
+	}
+
+private:
+	bool OnSocketReady(unsigned flags) noexcept override;
+	void OnIdle() noexcept override;
+};
+
+} // namespace Uring

src/event/meson.build

@@ -1,3 +1,9 @@
+event_sources = []
+
+if uring_dep.found()
+  event_sources += 'UringManager.cxx'
+endif
+
 event = static_library(
   'event',
   'PollGroupPoll.cxx',
@@ -15,10 +21,12 @@ event = static_library(
   'Call.cxx',
   'Thread.cxx',
   'Loop.cxx',
+  event_sources,
   include_directories: inc,
   dependencies: [
     boost_dep,
     log_dep,
+    uring_dep,
   ],
 )
 
@@ -29,5 +37,6 @@ event_dep = declare_dependency(
     net_dep,
     system_dep,
     boost_dep,
+    uring_dep,
   ],
 )