2 This file is a part of libcds - Concurrent Data Structures library
4 (C) Copyright Maxim Khizhinsky (libcds.dev@gmail.com) 2006-2016
6 Source code repo: http://github.com/khizmax/libcds/
7 Download: http://sourceforge.net/projects/libcds/files/
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10 modification, are permitted provided that the following conditions are met:
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13 list of conditions and the following disclaimer.
15 * Redistributions in binary form must reproduce the above copyright notice,
16 this list of conditions and the following disclaimer in the documentation
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31 #ifndef CDSLIB_INTRUSIVE_FREE_LIST_TAGGED_H
32 #define CDSLIB_INTRUSIVE_FREE_LIST_TAGGED_H
34 #include <cds/algo/atomic.h>
36 namespace cds { namespace intrusive {
38 /// Lock-free free list based on tagged pointers (required double-width CAS)
39 /** @ingroup cds_intrusive_helper
40 This variant of \p FreeList is intended for processor architectures that support double-width CAS.
41 It uses <a href="https://en.wikipedia.org/wiki/Tagged_pointer">tagged pointer</a> technique to solve ABA problem.
45 #include <cds/intrusive/free_list_tagged.h>
47 // Your struct should be derived from TaggedFreeList::node
48 struct Foo: public cds::intrusive::TaggedFreeList::node
53 // Simplified Foo allocator
57 // free-list clear() must be explicitly called before destroying the free-list object
60 m_FreeList.clear( []( freelist_node * p ) { delete static_cast<Foo *>( p ); });
65 freelist_node * p = m_FreeList.get();
67 return static_cast<Foo *>( p );
71 void dealloc( Foo * p )
73 m_FreeList.put( static_cast<freelist_node *>( p ));
77 typedef cds::intrusive::TaggedFreeList::node freelist_node;
78 cds::intrusive::TaggedFreeList m_FreeList;
87 atomics::atomic<node *> m_freeListNext;
90 : m_freeListNext( nullptr )
107 tagged_ptr( node* p )
113 static_assert(sizeof( tagged_ptr ) == sizeof( void * ) * 2, "sizeof( tagged_ptr ) violation");
117 /// Creates empty free-list
119 : m_Head( tagged_ptr())
121 // Your platform must support double-width CAS
122 assert( m_Head.is_lock_free());
125 /// Destroys the free list. Free-list must be empty.
127 @warning dtor does not free elements of the list.
128 To free elements you should manually call \p clear() with an appropriate disposer.
135 /// Puts \p pNode to the free list
136 void put( node * pNode )
138 assert( m_Head.is_lock_free());
140 tagged_ptr currentHead = m_Head.load( atomics::memory_order_relaxed );
141 tagged_ptr newHead = { pNode };
143 newHead.tag = currentHead.tag + 1;
144 pNode->m_freeListNext.store( currentHead.ptr, atomics::memory_order_relaxed );
145 } while ( cds_unlikely( !m_Head.compare_exchange_weak( currentHead, newHead, atomics::memory_order_release, atomics::memory_order_relaxed )));
148 /// Gets a node from the free list. If the list is empty, returns \p nullptr
151 tagged_ptr currentHead = m_Head.load( atomics::memory_order_acquire );
153 while ( currentHead.ptr != nullptr ) {
154 newHead.ptr = currentHead.ptr->m_freeListNext.load( atomics::memory_order_relaxed );
155 newHead.tag = currentHead.tag + 1;
156 if ( cds_likely( m_Head.compare_exchange_weak( currentHead, newHead, atomics::memory_order_release, atomics::memory_order_acquire )))
159 return currentHead.ptr;
162 /// Checks whether the free list is empty
165 return m_Head.load( atomics::memory_order_relaxed ).ptr == nullptr;
168 /// Clears the free list (not atomic)
170 For each element \p disp disposer is called to free memory.
171 The \p Disposer interface:
175 void operator()( FreeList::node * node );
179 This method must be explicitly called before the free list destructor.
181 template <typename Disposer>
182 void clear( Disposer disp )
184 node * head = m_Head.load( atomics::memory_order_relaxed ).ptr;
185 m_Head.store( { nullptr }, atomics::memory_order_relaxed );
187 node * next = head->m_freeListNext.load( atomics::memory_order_relaxed );
195 atomics::atomic<tagged_ptr> m_Head;
199 }} // namespace cds::intrusive
201 #endif // CDSLIB_INTRUSIVE_FREE_LIST_TAGGED_H