Template class for holding thread-local values during a parallel computation that will be merged into a final value.
template<typename T> class combinable;
#include "tbb/combinable.h"
A combinable<T> provides each thread with its own instance of type T.
namespace tbb { template <typename T> class combinable { public: combinable(); template <typename FInit> explicit combinable(FInit finit); combinable(const combinable& other); // Supported since C++11 combinable(combinable&& other); ~combinable(); combinable& operator=( const combinable& other); // Supported since C++11 combinable& operator=( combinable&& other); void clear(); T& local(); T& local(bool & exists); template<typename BinaryFunc> T combine(BinaryFunc f); template<typename UnaryFunc> void combine_each(UnaryFunc f); }; }
Member | Description |
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combinable() |
Constructs combinable such that thread-local instances of T will be default-constructed. |
template<typename FInit> explicit combinable(FInit finit) |
Constructs combinable such that thread-local elements will be created by copying the result of finit(). CAUTIONThe expression finit() must be safe to evaluate concurrently by multiple threads. It is evaluated each time a new thread-local element is created. |
combinable( const combinable& other ); |
Constructs a copy of other, so that it has copies of each element in other with the same thread mapping. |
combinable( combinable&& other ); |
Supported since C++11. Constructs combinable by moving the content of other intact. other is left in an unspecified state but can be safely destroyed. |
~combinable() |
Destroys all elements in *this. |
combinable& operator=( const combinable& other ) |
Sets *this to be a copy of other. |
combinable& operator=( combinable&& other ) |
Supported since C++11. Moves the content of other to *this intact. other is left in an unspecified state but can be safely destroyed. |
void clear() |
Removes all elements from *this. |
T& local() |
If an element does not exist for the current thread, creates it. Returns: Reference to thread-local element. |
T& local( bool& exists ) |
Similar to local(), except that exists is set to true if an element was already present for the current thread; false otherwise. Returns: Reference to thread-local element. |
template<typename BinaryFunc>T combine(BinaryFunc f) |
Requires: Parameter f should be an associative binary functor with the signature T(T,T) or T(const T&,const T&). Effects: Computes a reduction over all elements using binary functor f. All evaluations of f are done sequentially in the calling thread. If there are no elements, creates the result using the same rules as for creating a new element. Returns: Result of the reduction. |
template<typename UnaryFunc> void combine_each(UnaryFunc f) |
Requires: Parameter fshould be a unary functor with the signature void(T) or void(T&) or void(const T&). Effects: Evaluates f(x) for each thread-local element x in *this. All evaluations are done sequentially in the calling thread. |
Methods of class combinable are not thread-safe, except for local.