The namespace for functions applicable to the current task_arena.

The namespace this_task_arena contains global functions for interaction with the task_arena currently used by the calling thread.

// Defined in header <tbb/task_arena.h>

namespace tbb {
    namespace this_task_arena {
        int current_thread_index();
        int max_concurrency();
        template<typename F> auto isolate(F&& f) -> decltype(f());
int current_thread_index()

Returns the thread index in a task_arena currently used by the calling thread, or task_arena::not_initialized if the thread has not yet initialized the task scheduler.

A thread index is an integer number between 0 and the task_arena concurrency level. Thread indexes are assigned to both application threads and worker threads on joining an arena and are kept until exiting the arena. Indexes of threads that share an arena are unique - i.e. no two threads within the arena may have the same index at the same time - but not necessarily consecutive.


Since a thread may exit the arena at any time if it does not execute a task, the index of a thread may change between any two tasks, even those belonging to the same task group or algorithm.


Threads that use different arenas may have the same current index value.


Joining a nested arena in execute() may change current index value while preserving the index in the outer arena which will be restored on return.

int max_concurrency()

Returns the concurrency level of the task_arena currently used by the calling thread. If the thread has not yet initialized the task scheduler, returns the concurrency level determined automatically for the hardware configuration.

auto isolate(F &&f) -> decltype(f())

Runs the specified functor in isolation by restricting the calling thread to process only tasks scheduled in the scope of the functor (also called the isolation region). The function returns the value returned by the functor. The F type shall meet the Function Objects requirements from [function.objects] ISO C++ Standard section.


The object returned by the functor cannot be a reference. std::reference_wrapper can be used instead.