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diff --git a/src/lib/nfs/Cancellable.hxx b/src/lib/nfs/Cancellable.hxx
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+/*
+ * Copyright (C) 2003-2014 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_NFS_CANCELLABLE_HXX
+#define MPD_NFS_CANCELLABLE_HXX
+
+#include "Compiler.h"
+
+#include <boost/intrusive/list.hpp>
+
+#include <algorithm>
+
+#include <assert.h>
+
+template<typename T>
+class CancellablePointer
+ : public boost::intrusive::list_base_hook<boost::intrusive::link_mode<boost::intrusive::normal_link>> {
+public:
+ typedef T *pointer_type;
+ typedef T &reference_type;
+ typedef const T &const_reference_type;
+
+private:
+ pointer_type p;
+
+public:
+ explicit CancellablePointer(reference_type _p):p(&_p) {}
+
+ CancellablePointer(const CancellablePointer &) = delete;
+
+ constexpr bool IsCancelled() const {
+ return p == nullptr;
+ }
+
+ void Cancel() {
+ assert(!IsCancelled());
+
+ p = nullptr;
+ }
+
+ reference_type Get() {
+ assert(p != nullptr);
+
+ return *p;
+ }
+
+ constexpr bool Is(const_reference_type other) const {
+ return p == &other;
+ }
+};
+
+template<typename T, typename CT=CancellablePointer<T>>
+class CancellableList {
+public:
+ typedef typename CT::reference_type reference_type;
+ typedef typename CT::const_reference_type const_reference_type;
+
+private:
+ typedef boost::intrusive::list<CT,
+ boost::intrusive::constant_time_size<false>> List;
+ typedef typename List::iterator iterator;
+ typedef typename List::const_iterator const_iterator;
+ List list;
+
+ class MatchPointer {
+ const_reference_type p;
+
+ public:
+ explicit constexpr MatchPointer(const_reference_type _p)
+ :p(_p) {}
+
+ constexpr bool operator()(const CT &a) const {
+ return a.Is(p);
+ }
+ };
+
+ gcc_pure
+ iterator Find(reference_type p) {
+ return std::find_if(list.begin(), list.end(), MatchPointer(p));
+ }
+
+ gcc_pure
+ const_iterator Find(const_reference_type p) const {
+ return std::find_if(list.begin(), list.end(), MatchPointer(p));
+ }
+
+ gcc_pure
+ iterator Find(CT &c) {
+ return list.iterator_to(c);
+ }
+
+ gcc_pure
+ const_iterator Find(const CT &c) const {
+ return list.iterator_to(c);
+ }
+
+public:
+#ifndef NDEBUG
+ gcc_pure
+ bool IsEmpty() const {
+ for (const auto &c : list)
+ if (!c.IsCancelled())
+ return false;
+
+ return true;
+ }
+#endif
+
+ gcc_pure
+ bool Contains(const_reference_type p) const {
+ return Find(p) != list.end();
+ }
+
+ template<typename... Args>
+ CT &Add(reference_type p, Args&&... args) {
+ assert(Find(p) == list.end());
+
+ CT *c = new CT(p, std::forward<Args>(args)...);
+ list.push_back(*c);
+ return *c;
+ }
+
+ void Remove(CT &ct) {
+ auto i = Find(ct);
+ assert(i != list.end());
+
+ list.erase(i);
+ delete &ct;
+ }
+
+ void Cancel(reference_type p) {
+ auto i = Find(p);
+ assert(i != list.end());
+
+ i->Cancel();
+ }
+
+ CT &Get(reference_type p) {
+ auto i = Find(p);
+ assert(i != list.end());
+
+ return *i;
+ }
+
+ template<typename F>
+ void ForEach(F &&f) {
+ for (CT &i : list)
+ f(i);
+ }
+};
+
+#endif