Otherwise it detaches the current thread from Hazard Pointer GC.
*/
~thread_gc() ; // inline in hp_impl.h
+
+ public: // for internal use only!!!
+ //@cond
+ static cds::gc::hp::details::hp_guard& alloc_guard(); // inline in hp_impl.h
+ static void free_guard( cds::gc::hp::details::hp_guard& g ); // inline in hp_impl.h
+ //@endcond
};
/// Hazard Pointer guard
}
};
+ /// Guarded pointer
+ /**
+ A guarded pointer is a pair of a pointer and GC's guard.
+ Usually, it is used for returning a pointer to the item from an lock-free container.
+ The guard prevents the pointer to be early disposed (freed) by GC.
+ After destructing \p %guarded_ptr object the pointer can be disposed (freed) automatically at any time.
+
+ Template arguments:
+ - \p GuardedType - a type which the guard stores
+ - \p ValueType - a value type
+ - \p Cast - a functor for converting <tt>GuardedType*</tt> to <tt>ValueType*</tt>. Default is \p void (no casting).
+
+ For intrusive containers, \p GuardedType is the same as \p ValueType and no casting is needed.
+ In such case the \p %guarded_ptr is:
+ @code
+ typedef cds::gc::HP::guarded_ptr< foo > intrusive_guarded_ptr;
+ @endcode
+
+ For standard (non-intrusive) containers \p GuardedType is not the same as \p ValueType and casting is needed.
+ For example:
+ @code
+ struct foo {
+ int const key;
+ std::string value;
+ };
+
+ struct value_accessor {
+ std::string* operator()( foo* pFoo ) const
+ {
+ return &(pFoo->value);
+ }
+ };
+
+ // Guarded ptr
+ typedef cds::gc::HP::guarded_ptr< Foo, std::string, value_accessor > nonintrusive_guarded_ptr;
+ @endcode
+
+ You don't need use this class directly.
+ All set/map container classes from \p libcds declare the typedef for \p %guarded_ptr with appropriate casting functor.
+ */
+ template <typename GuardedType, typename ValueType=GuardedType, typename Cast=void >
+ class guarded_ptr
+ {
+ //@cond
+ struct trivial_cast {
+ ValueType * operator()( GuardedType * p ) const
+ {
+ return p;
+ }
+ };
+ //@endcond
+
+ public:
+ typedef GuardedType guarded_type; ///< Guarded type
+ typedef ValueType value_type; ///< Value type
+
+ /// Functor for casting \p guarded_type to \p value_type
+ typedef typename std::conditional< std::is_same<Cast, void>::value, trivial_cast, Cast >::type value_cast;
+
+ //@cond
+ typedef cds::gc::hp::details::hp_guard native_guard;
+ //@endcond
+
+ private:
+ //@cond
+ native_guard * m_pGuard;
+ //@endcond
+
+ public:
+ /// Creates empty guarded pointer
+ guarded_ptr() CDS_NOEXCEPT
+ : m_pGuard(nullptr)
+ {}
+
+ //@cond
+ /// Initializes guarded pointer with \p p
+ explicit guarded_ptr( guarded_type * p ) CDS_NOEXCEPT
+ {
+ alloc_guard();
+ assert( m_pGuard );
+ m_pGuard->set(p);
+ }
+ explicit guarded_ptr( std::nullptr_t ) CDS_NOEXCEPT
+ : m_pGuard( nullptr )
+ {}
+ //@endcond
+
+ /// Move ctor
+ guarded_ptr( guarded_ptr&& gp ) CDS_NOEXCEPT
+ : m_pGuard( gp.m_pGuard )
+ {
+ gp.m_pGuard = nullptr;
+ }
+
+ /// The guarded pointer is not copy-constructible
+ guarded_ptr( guarded_ptr const& gp ) = delete;
+
+ /// Clears the guarded pointer
+ /**
+ \ref release is called if guarded pointer is not \ref empty
+ */
+ ~guarded_ptr() CDS_NOEXCEPT
+ {
+ free_guard();
+ }
+
+ /// Move-assignment operator
+ guarded_ptr& operator=( guarded_ptr&& gp ) CDS_NOEXCEPT
+ {
+ // Hazard Pointer array is organized as a stack
+ if ( m_pGuard && m_pGuard > gp.m_pGuard ) {
+ m_pGuard->set( gp.m_pGuard->get(atomics::memory_order_relaxed) );
+ gp.free_guard();
+ }
+ else {
+ free_guard();
+ m_pGuard = gp.m_pGuard;
+ gp.m_pGuard = nullptr;
+ }
+ return *this;
+ }
+
+ /// The guarded pointer is not copy-assignable
+ guarded_ptr& operator=(guarded_ptr const& gp) = delete;
+
+ /// Returns a pointer to guarded value
+ value_type * operator ->() const CDS_NOEXCEPT
+ {
+ assert( !empty() );
+ return value_cast()( reinterpret_cast<guarded_type *>(m_pGuard->get()));
+ }
+
+ /// Returns a reference to guarded value
+ value_type& operator *() CDS_NOEXCEPT
+ {
+ assert( !empty());
+ return *value_cast()(reinterpret_cast<guarded_type *>(m_pGuard->get()));
+ }
+
+ /// Returns const reference to guarded value
+ value_type const& operator *() const CDS_NOEXCEPT
+ {
+ assert( !empty() );
+ return *value_cast()(reinterpret_cast<guarded_type *>(m_pGuard->get()));
+ }
+
+ /// Checks if the guarded pointer is \p nullptr
+ bool empty() const CDS_NOEXCEPT
+ {
+ return !m_pGuard || m_pGuard->get( atomics::memory_order_relaxed ) == nullptr;
+ }
+
+ /// \p bool operator returns <tt>!empty()</tt>
+ explicit operator bool() const CDS_NOEXCEPT
+ {
+ return !empty();
+ }
+
+ /// Clears guarded pointer
+ /**
+ If the guarded pointer has been released, the pointer can be disposed (freed) at any time.
+ Dereferncing the guarded pointer after \p release() is dangerous.
+ */
+ void release() CDS_NOEXCEPT
+ {
+ if ( m_pGuard )
+ m_pGuard->clear();
+ }
+
+ //@cond
+ // For internal use only!!!
+ native_guard& guard() CDS_NOEXCEPT
+ {
+ alloc_guard();
+ assert( m_pGuard );
+ return *m_pGuard;
+ }
+ //@endcond
+
+ private:
+ //@cond
+ void alloc_guard()
+ {
+ if ( !m_pGuard )
+ m_pGuard = &thread_gc::alloc_guard();
+ }
+
+ void free_guard()
+ {
+ if ( m_pGuard ) {
+ thread_gc::free_guard( *m_pGuard );
+ m_pGuard = nullptr;
+ }
+ }
+ //@endcond
+ };
+
public:
/// \p scan() type
enum class scan_type {
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