input/cache: first draft of the file cache

9 files changed, 729 insertions, 0 deletions

diff --git a/src/input/cache/Config.cxx b/src/input/cache/Config.cxx
new file mode 100644
index 000000000..efb472497
--- /dev/null
+++ b/src/input/cache/Config.cxx
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2003-2019 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.hxx"
+#include "config/Block.hxx"
+#include "config/Parser.hxx"
+
+static constexpr size_t KILOBYTE = 1024;
+static constexpr size_t MEGABYTE = 1024 * KILOBYTE;
+
+InputCacheConfig::InputCacheConfig(const ConfigBlock &block)
+{
+	size = 256 * MEGABYTE;
+	const auto *size_param = block.GetBlockParam("size");
+	if (size_param != nullptr)
+		size = size_param->With([](const char *s){
+			return ParseSize(s);
+		});
+}
diff --git a/src/input/cache/Config.hxx b/src/input/cache/Config.hxx
new file mode 100644
index 000000000..3ea1c551c
--- /dev/null
+++ b/src/input/cache/Config.hxx
@@ -0,0 +1,33 @@
+/*
+ * Copyright 2003-2019 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_INPUT_CACHE_CONFIG_HXX
+#define MPD_INPUT_CACHE_CONFIG_HXX
+
+#include <stddef.h>
+
+struct ConfigBlock;
+
+struct InputCacheConfig {
+	size_t size;
+
+	explicit InputCacheConfig(const ConfigBlock &block);
+};
+
+#endif
diff --git a/src/input/cache/Item.cxx b/src/input/cache/Item.cxx
new file mode 100644
index 000000000..5decaaced
--- /dev/null
+++ b/src/input/cache/Item.cxx
@@ -0,0 +1,62 @@
+/*
+ * Copyright 2003-2019 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 "Item.hxx"
+#include "Lease.hxx"
+
+#include <assert.h>
+
+InputCacheItem::InputCacheItem(InputStreamPtr _input) noexcept
+	:BufferingInputStream(std::move(_input)),
+	 uri(GetInput().GetURI())
+{
+}
+
+InputCacheItem::~InputCacheItem() noexcept
+{
+	assert(leases.empty());
+}
+
+void
+InputCacheItem::AddLease(InputCacheLease &lease) noexcept
+{
+	const std::lock_guard<Mutex> lock(mutex);
+	leases.push_back(lease);
+}
+
+void
+InputCacheItem::RemoveLease(InputCacheLease &lease) noexcept
+{
+	const std::lock_guard<Mutex> lock(mutex);
+	auto i = leases.iterator_to(lease);
+	if (i == next_lease)
+		++next_lease;
+	leases.erase(i);
+
+	// TODO: ensure that OnBufferAvailable() isn't currently running
+}
+
+void
+InputCacheItem::OnBufferAvailable() noexcept
+{
+	for (auto i = leases.begin(); i != leases.end(); i = next_lease) {
+		next_lease = std::next(i);
+		i->OnInputCacheAvailable();
+	}
+}
diff --git a/src/input/cache/Item.hxx b/src/input/cache/Item.hxx
new file mode 100644
index 000000000..53b9668a1
--- /dev/null
+++ b/src/input/cache/Item.hxx
@@ -0,0 +1,80 @@
+/*
+ * Copyright 2003-2019 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_INPUT_CACHE_ITEM_HXX
+#define MPD_INPUT_CACHE_ITEM_HXX
+
+#include "input/BufferingInputStream.hxx"
+#include "thread/Mutex.hxx"
+#include "util/SparseBuffer.hxx"
+
+#include <boost/intrusive/list.hpp>
+#include <boost/intrusive/set_hook.hpp>
+
+#include <memory>
+#include <string>
+
+class InputCacheLease;
+
+/**
+ * An item in the #InputCacheManager.  It caches the contents of a
+ * file, and reading and managing it through the base class
+ * #BufferingInputStream.
+ *
+ * Use the class #CacheInputStream to read from it.
+ */
+class InputCacheItem final
+	: public BufferingInputStream,
+	  public boost::intrusive::list_base_hook<boost::intrusive::link_mode<boost::intrusive::auto_unlink>>,
+	  public boost::intrusive::set_base_hook<boost::intrusive::link_mode<boost::intrusive::normal_link>>
+{
+	const std::string uri;
+
+	using LeaseList =
+		boost::intrusive::list<InputCacheLease,
+				       boost::intrusive::base_hook<boost::intrusive::list_base_hook<boost::intrusive::link_mode<boost::intrusive::normal_link>>>,
+				       boost::intrusive::constant_time_size<false>>;
+
+	LeaseList leases;
+	LeaseList::iterator next_lease = leases.end();
+
+public:
+	explicit InputCacheItem(InputStreamPtr _input) noexcept;
+	~InputCacheItem() noexcept;
+
+	const char *GetUri() const noexcept {
+		return uri.c_str();
+	}
+
+	using BufferingInputStream::size;
+
+	bool IsInUse() const noexcept {
+		const std::lock_guard<Mutex> lock(mutex);
+		return !leases.empty();
+	}
+
+	void AddLease(InputCacheLease &lease) noexcept;
+	void RemoveLease(InputCacheLease &lease) noexcept;
+
+private:
+	/* virtual methods from class BufferingInputStream */
+	void OnBufferAvailable() noexcept override;
+};
+
+#endif
diff --git a/src/input/cache/Lease.hxx b/src/input/cache/Lease.hxx
new file mode 100644
index 000000000..be0380e84
--- /dev/null
+++ b/src/input/cache/Lease.hxx
@@ -0,0 +1,94 @@
+/*
+ * Copyright 2003-2019 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_INPUT_CACHE_LEASE_HXX
+#define MPD_INPUT_CACHE_LEASE_HXX
+
+#include "Item.hxx"
+
+#include <boost/intrusive/list_hook.hpp>
+
+#include <utility>
+
+/**
+ * A lease for an #InputCacheItem.
+ */
+class InputCacheLease
+	: public boost::intrusive::list_base_hook<boost::intrusive::link_mode<boost::intrusive::normal_link>>
+{
+	InputCacheItem *item = nullptr;
+
+public:
+	InputCacheLease() = default;
+
+	explicit InputCacheLease(InputCacheItem &_item) noexcept
+		:item(&_item)
+	{
+		item->AddLease(*this);
+	}
+
+	InputCacheLease(InputCacheLease &&src) noexcept
+		:item(std::exchange(src.item, nullptr))
+	{
+		if (item != nullptr) {
+			item->RemoveLease(src);
+			item->AddLease(*this);
+		}
+	}
+
+	~InputCacheLease() noexcept {
+		if (item != nullptr)
+			item->RemoveLease(*this);
+	}
+
+	InputCacheLease &operator=(InputCacheLease &&src) noexcept {
+		using std::swap;
+		swap(item, src.item);
+
+		if (item != nullptr) {
+			item->RemoveLease(src);
+			item->AddLease(*this);
+		}
+
+		return *this;
+	}
+
+	operator bool() const noexcept {
+		return item != nullptr;
+	}
+
+	auto &operator*() const noexcept {
+		return *item;
+	}
+
+	auto *operator->() const noexcept {
+		return item;
+	}
+
+	auto &GetCacheItem() const noexcept {
+		return *item;
+	}
+
+	/**
+	 * Caller locks #InputCacheItem::mutex.
+	 */
+	virtual void OnInputCacheAvailable() noexcept {}
+};
+
+#endif
diff --git a/src/input/cache/Manager.cxx b/src/input/cache/Manager.cxx
new file mode 100644
index 000000000..3ff51d88e
--- /dev/null
+++ b/src/input/cache/Manager.cxx
@@ -0,0 +1,163 @@
+/*
+ * Copyright 2003-2019 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 "Manager.hxx"
+#include "Config.hxx"
+#include "Item.hxx"
+#include "Lease.hxx"
+#include "input/InputStream.hxx"
+#include "fs/Traits.hxx"
+#include "util/DeleteDisposer.hxx"
+
+#include <string.h>
+
+inline bool
+InputCacheManager::ItemCompare::operator()(const InputCacheItem &a,
+					   const char *b) const noexcept
+{
+	return strcmp(a.GetUri(), b) < 0;
+}
+
+inline bool
+InputCacheManager::ItemCompare::operator()(const char *a,
+					   const InputCacheItem &b) const noexcept
+{
+	return strcmp(a, b.GetUri()) < 0;
+}
+
+inline bool
+InputCacheManager::ItemCompare::operator()(const InputCacheItem &a,
+					   const InputCacheItem &b) const noexcept
+{
+	return strcmp(a.GetUri(), b.GetUri()) < 0;
+}
+
+InputCacheManager::InputCacheManager(const InputCacheConfig &config) noexcept
+	:max_total_size(config.size)
+{
+}
+
+InputCacheManager::~InputCacheManager() noexcept
+{
+	items_by_time.clear_and_dispose(DeleteDisposer());
+}
+
+bool
+InputCacheManager::IsEligible(const InputStream &input) noexcept
+{
+	assert(input.IsReady());
+
+	return input.IsSeekable() && input.KnownSize() &&
+		input.GetSize() > 0 &&
+		input.GetSize() <= max_total_size / 2;
+}
+
+bool
+InputCacheManager::Contains(const char *uri) noexcept
+{
+	return Get(uri, false);
+}
+
+InputCacheLease
+InputCacheManager::Get(const char *uri, bool create)
+{
+	// TODO: allow caching remote files
+	if (!PathTraitsUTF8::IsAbsolute(uri))
+		return {};
+
+	UriMap::insert_commit_data hint;
+	auto result = items_by_uri.insert_check(uri, items_by_uri.key_comp(),
+						hint);
+	if (!result.second) {
+		auto &item = *result.first;
+
+		/* refresh */
+		items_by_time.erase(items_by_time.iterator_to(item));
+		items_by_time.push_back(item);
+
+		// TODO revalidate the cache item using the file's mtime?
+		// TODO if cache item contains error, retry now?
+
+		return InputCacheLease(item);
+	}
+
+	if (!create)
+		return {};
+
+	// TODO: wait for "ready" without blocking here
+	auto is = InputStream::OpenReady(uri, mutex);
+
+	if (!IsEligible(*is))
+		return {};
+
+	const size_t size = is->GetSize();
+	total_size += size;
+
+	while (total_size > max_total_size && EvictOldestUnused()) {}
+
+	auto *item = new InputCacheItem(std::move(is));
+	items_by_uri.insert_commit(*item, hint);
+	items_by_time.push_back(*item);
+
+	return InputCacheLease(*item);
+}
+
+void
+InputCacheManager::Prefetch(const char *uri)
+{
+	Get(uri, true);
+}
+
+void
+InputCacheManager::Remove(InputCacheItem &item) noexcept
+{
+	assert(total_size >= item.size());
+	total_size -= item.size();
+
+	items_by_time.erase(items_by_time.iterator_to(item));
+	items_by_uri.erase(items_by_uri.iterator_to(item));
+}
+
+void
+InputCacheManager::Delete(InputCacheItem *item) noexcept
+{
+	Remove(*item);
+	delete item;
+}
+
+InputCacheItem *
+InputCacheManager::FindOldestUnused() noexcept
+{
+	for (auto &i : items_by_time)
+		if (!i.IsInUse())
+			return &i;
+
+	return nullptr;
+}
+
+bool
+InputCacheManager::EvictOldestUnused() noexcept
+{
+	auto *item = FindOldestUnused();
+	if (item == nullptr)
+		return false;
+
+	Delete(item);
+	return true;
+}
diff --git a/src/input/cache/Manager.hxx b/src/input/cache/Manager.hxx
new file mode 100644
index 000000000..6fba1fbb3
--- /dev/null
+++ b/src/input/cache/Manager.hxx
@@ -0,0 +1,114 @@
+/*
+ * Copyright 2003-2019 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_INPUT_CACHE_MANAGER_HXX
+#define MPD_INPUT_CACHE_MANAGER_HXX
+
+#include "input/Offset.hxx"
+#include "thread/Mutex.hxx"
+#include "util/Compiler.h"
+
+#include <boost/intrusive/set.hpp>
+#include <boost/intrusive/list.hpp>
+
+class InputStream;
+class InputCacheItem;
+class InputCacheLease;
+struct InputCacheConfig;
+
+/**
+ * A class which caches files in RAM.  It is supposed to prefetch
+ * files before they are played.
+ */
+class InputCacheManager {
+	const size_t max_total_size;
+
+	mutable Mutex mutex;
+
+	size_t total_size = 0;
+
+	struct ItemCompare {
+		gcc_pure
+		bool operator()(const InputCacheItem &a,
+				const char *b) const noexcept;
+
+		gcc_pure
+		bool operator()(const char *a,
+				const InputCacheItem &b) const noexcept;
+
+		gcc_pure
+		bool operator()(const InputCacheItem &a,
+				const InputCacheItem &b) const noexcept;
+	};
+
+	boost::intrusive::list<InputCacheItem,
+			       boost::intrusive::base_hook<boost::intrusive::list_base_hook<boost::intrusive::link_mode<boost::intrusive::auto_unlink>>>,
+			       boost::intrusive::constant_time_size<false>> items_by_time;
+
+	using UriMap =
+		boost::intrusive::set<InputCacheItem,
+				      boost::intrusive::base_hook<boost::intrusive::set_base_hook<boost::intrusive::link_mode<boost::intrusive::normal_link>>>,
+				      boost::intrusive::compare<ItemCompare>,
+				      boost::intrusive::constant_time_size<false>>;
+
+	UriMap items_by_uri;
+
+public:
+	explicit InputCacheManager(const InputCacheConfig &config) noexcept;
+	~InputCacheManager() noexcept;
+
+	gcc_pure
+	bool Contains(const char *uri) noexcept;
+
+	/**
+	 * Throws if opening the #InputStream fails.
+	 *
+	 * @param create if true, then the cache item will be created
+	 * if it did not exist
+	 * @return a lease of the new item or nullptr if the file is
+	 * not eligible for caching
+	 */
+	InputCacheLease Get(const char *uri, bool create);
+
+	/**
+	 * Shortcut for "Get(uri,true)", discarding the returned
+	 * lease.
+	 */
+	void Prefetch(const char *uri);
+
+private:
+	/**
+	 * Check whether the given #InputStream can be stored in this
+	 * cache.
+	 */
+	bool IsEligible(const InputStream &input) noexcept;
+
+	void Remove(InputCacheItem &item) noexcept;
+	void Delete(InputCacheItem *item) noexcept;
+
+	InputCacheItem *FindOldestUnused() noexcept;
+
+	/**
+	 * @return true if one item has been evicted, false if no
+	 * unused item was found
+	 */
+	bool EvictOldestUnused() noexcept;
+};
+
+#endif
diff --git a/src/input/cache/Stream.cxx b/src/input/cache/Stream.cxx
new file mode 100644
index 000000000..5ce56eaef
--- /dev/null
+++ b/src/input/cache/Stream.cxx
@@ -0,0 +1,96 @@
+/*
+ * Copyright 2003-2019 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 "Stream.hxx"
+
+CacheInputStream::CacheInputStream(InputCacheLease _lease,
+				   Mutex &_mutex) noexcept
+	:InputStream(_lease->GetUri(), _mutex),
+	 InputCacheLease(std::move(_lease))
+{
+	auto &i = GetCacheItem();
+	size = i.size();
+	seekable = true;
+	SetReady();
+}
+
+void
+CacheInputStream::Check()
+{
+	const ScopeUnlock unlock(mutex);
+
+	auto &i = GetCacheItem();
+	const std::lock_guard<Mutex> protect(i.mutex);
+
+	i.Check();
+}
+
+void
+CacheInputStream::Seek(std::unique_lock<Mutex> &, offset_type new_offset)
+{
+	offset = new_offset;
+}
+
+bool
+CacheInputStream::IsEOF() const noexcept
+{
+	return offset == size;
+}
+
+bool
+CacheInputStream::IsAvailable() const noexcept
+{
+	const auto _offset = offset;
+	const ScopeUnlock unlock(mutex);
+
+	auto &i = GetCacheItem();
+	const std::lock_guard<Mutex> protect(i.mutex);
+
+	return i.IsAvailable(_offset);
+}
+
+size_t
+CacheInputStream::Read(std::unique_lock<Mutex> &lock,
+		       void *ptr, size_t read_size)
+{
+	const auto _offset = offset;
+	auto &i = GetCacheItem();
+
+	size_t nbytes;
+
+	{
+		const ScopeUnlock unlock(mutex);
+		const std::lock_guard<Mutex> protect(i.mutex);
+
+		nbytes = i.Read(lock, _offset, ptr, read_size);
+	}
+
+	offset += nbytes;
+	return nbytes;
+}
+
+void
+CacheInputStream::OnInputCacheAvailable() noexcept
+{
+	auto &i = GetCacheItem();
+	const ScopeUnlock unlock(i.mutex);
+
+	const std::lock_guard<Mutex> protect(mutex);
+	InvokeOnAvailable();
+}
diff --git a/src/input/cache/Stream.hxx b/src/input/cache/Stream.hxx
new file mode 100644
index 000000000..ae039359c
--- /dev/null
+++ b/src/input/cache/Stream.hxx
@@ -0,0 +1,52 @@
+/*
+ * Copyright 2003-2019 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_CACHE_INPUT_STREAM_HXX
+#define MPD_CACHE_INPUT_STREAM_HXX
+
+#include "Lease.hxx"
+#include "input/InputStream.hxx"
+
+/**
+ * An #InputStream implementation which reads data from an
+ * #InputCacheItem.
+ */
+class CacheInputStream final : public InputStream, InputCacheLease {
+public:
+	CacheInputStream(InputCacheLease _lease, Mutex &_mutex) noexcept;
+
+	/* virtual methods from class InputStream */
+	void Check() override;
+	/* we don't need to implement Update() because all attributes
+	   have been copied already in our constructor */
+	//void Update() noexcept;
+	void Seek(std::unique_lock<Mutex> &lock, offset_type offset) override;
+	bool IsEOF() const noexcept override;
+	/* we don't support tags */
+	// std::unique_ptr<Tag> ReadTag() override;
+	bool IsAvailable() const noexcept override;
+	size_t Read(std::unique_lock<Mutex> &lock,
+		    void *ptr, size_t size) override;
+
+private:
+	/* virtual methods from class InputCacheLease */
+	void OnInputCacheAvailable() noexcept override;
+};
+
+#endif