input/LastInputStream: new class

src/input/LastInputStream.cxx

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2003-2021 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 "LastInputStream.hxx"
+#include "InputStream.hxx"
+
+#include <cassert>
+
+LastInputStream::LastInputStream(EventLoop &event_loop) noexcept
+	:close_timer(event_loop, BIND_THIS_METHOD(OnCloseTimer))
+{
+}
+
+LastInputStream::~LastInputStream() noexcept = default;
+
+void
+LastInputStream::Close() noexcept
+{
+	is.reset();
+	close_timer.Cancel();
+}
+
+void
+LastInputStream::OnCloseTimer() noexcept
+{
+	assert(is);
+
+	is.reset();
+}

src/input/LastInputStream.hxx

@@ -0,0 +1,86 @@
+/*
+ * Copyright 2003-2021 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_LAST_INPUT_STREAM_HXX
+#define MPD_LAST_INPUT_STREAM_HXX
+
+#include "Ptr.hxx"
+#include "thread/Mutex.hxx"
+#include "event/TimerEvent.hxx"
+
+#include <string>
+
+/**
+ * A helper class which maintains an #InputStream that is opened once
+ * and may be reused later for some time.  It will be closed
+ * automatically after some time.
+ *
+ * This class is not thread-safe.  All methods must be called on the
+ * thread which runs the #EventLoop.
+ */
+class LastInputStream {
+	std::string uri;
+
+	Mutex mutex;
+
+	InputStreamPtr is;
+
+	TimerEvent close_timer;
+
+public:
+	explicit LastInputStream(EventLoop &event_loop) noexcept;
+	~LastInputStream() noexcept;
+
+	/**
+	 * Open an #InputStream instance with the given opener
+	 * function, but returns the cached instance if it matches.
+	 *
+	 * This object keeps owning the #InputStream; the caller shall
+	 * not close it.
+	 */
+	template<typename U, typename O>
+	InputStream *Open(U &&new_uri, O &&open) {
+		if (new_uri == uri) {
+			if (is)
+				/* refresh the timeout */
+				ScheduleClose();
+
+			return is.get();
+		}
+
+		is.reset();
+		close_timer.Cancel();
+
+		is = open(new_uri, mutex);
+		uri = std::forward<U>(new_uri);
+		ScheduleClose();
+		return is.get();
+	}
+
+	void Close() noexcept;
+
+private:
+	void ScheduleClose() noexcept {
+		close_timer.Schedule(std::chrono::seconds(20));
+	}
+
+	void OnCloseTimer() noexcept;
+};
+
+#endif

src/input/meson.build

@@ -8,6 +8,7 @@ input_api = static_library(
   'ThreadInputStream.cxx',
   'AsyncInputStream.cxx',
   'ProxyInputStream.cxx',
+  'LastInputStream.cxx',
   include_directories: inc,
   dependencies: [
     boost_dep,