2 This file is a part of libcds - Concurrent Data Structures library
4 (C) Copyright Maxim Khizhinsky (libcds.dev@gmail.com) 2006-2017
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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19 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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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_freelist
41 This variant of \p FreeList is intended for processor architectures that support double-width CAS.
42 It uses <a href="https://en.wikipedia.org/wiki/Tagged_pointer">tagged pointer</a> technique to solve ABA problem.
46 #include <cds/intrusive/free_list_tagged.h>
48 // Your struct should be derived from TaggedFreeList::node
49 struct Foo: public cds::intrusive::TaggedFreeList::node
54 // Simplified Foo allocator
58 // free-list clear() must be explicitly called before destroying the free-list object
61 m_FreeList.clear( []( freelist_node * p ) { delete static_cast<Foo *>( p ); });
66 freelist_node * p = m_FreeList.get();
68 return static_cast<Foo *>( p );
72 void dealloc( Foo * p )
74 m_FreeList.put( static_cast<freelist_node *>( p ));
78 typedef cds::intrusive::TaggedFreeList::node freelist_node;
79 cds::intrusive::TaggedFreeList m_FreeList;
88 atomics::atomic<node *> m_freeListNext;
92 m_freeListNext.store( nullptr, atomics::memory_order_release );
109 tagged_ptr( node* p )
115 static_assert(sizeof( tagged_ptr ) == sizeof( void * ) * 2, "sizeof( tagged_ptr ) violation");
119 /// Creates empty free-list
121 : m_Head( tagged_ptr())
123 // Your platform must support double-width CAS
124 assert( m_Head.is_lock_free());
127 /// Destroys the free list. Free-list must be empty.
129 @warning dtor does not free elements of the list.
130 To free elements you should manually call \p clear() with an appropriate disposer.
137 /// Puts \p pNode to the free list
138 void put( node * pNode )
140 assert( m_Head.is_lock_free());
142 tagged_ptr currentHead = m_Head.load( atomics::memory_order_relaxed );
143 tagged_ptr newHead = { pNode };
145 newHead.tag = currentHead.tag + 1;
146 pNode->m_freeListNext.store( currentHead.ptr, atomics::memory_order_relaxed );
147 CDS_TSAN_ANNOTATE_HAPPENS_BEFORE( &pNode->m_freeListNext );
148 } while ( cds_unlikely( !m_Head.compare_exchange_weak( currentHead, newHead, atomics::memory_order_release, atomics::memory_order_acquire )));
151 /// Gets a node from the free list. If the list is empty, returns \p nullptr
154 tagged_ptr currentHead = m_Head.load( atomics::memory_order_acquire );
156 while ( currentHead.ptr != nullptr ) {
157 CDS_TSAN_ANNOTATE_HAPPENS_AFTER( ¤tHead.ptr->m_freeListNext );
158 newHead.ptr = currentHead.ptr->m_freeListNext.load( atomics::memory_order_relaxed );
159 newHead.tag = currentHead.tag + 1;
160 if ( cds_likely( m_Head.compare_exchange_weak( currentHead, newHead, atomics::memory_order_release, atomics::memory_order_acquire )))
163 return currentHead.ptr;
166 /// Checks whether the free list is empty
169 return m_Head.load( atomics::memory_order_relaxed ).ptr == nullptr;
172 /// Clears the free list (not atomic)
174 For each element \p disp disposer is called to free memory.
175 The \p Disposer interface:
179 void operator()( FreeList::node * node );
183 This method must be explicitly called before the free list destructor.
185 template <typename Disposer>
186 void clear( Disposer disp )
188 node * head = m_Head.load( atomics::memory_order_relaxed ).ptr;
189 m_Head.store( { nullptr }, atomics::memory_order_relaxed );
191 node * next = head->m_freeListNext.load( atomics::memory_order_relaxed );
199 atomics::atomic<tagged_ptr> m_Head;
203 }} // namespace cds::intrusive
205 #endif // CDSLIB_INTRUSIVE_FREE_LIST_TAGGED_H