input/cache: first draft of the file cache

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;
+}