TBB abstracts out threads/OS/hardware so the developers work with TBB tasks instead. So, the current_thread_index() is not supposed to be often used in a sense that thread IDs normally not needed if we use TBB main model of working with tasks. However, for some workloads, for example, typical HPC workload which is regular (i.e., for loops) instead of irregular workloads TBB was designed for, TBB team published examples that assign thread affinities and use current_thread_index() together with other APIs for that.
I suggest to download a free copy of proTBB book from https://www.apress.com/gp/book/9781484243978. From page 360 there:
"
Figure 13-1 shows a simple example of how to use a task_scheduler_observer object to pin threads to cores on Linux. In this example, we use the sched_setaffinity function to set the CPU mask for each thread as it joins the default arena. In Chapter 20, we show an example that assigns affinity using the hwloc software package. In the example in Figure 13-1, we use tbb::this_task_arena::max_concurrency() to find the number of slots in the arena and tbb::this_task_arena::current_thread_index() to find the slot that the calling thread is assigned to. Since we know there will be the same number of slots in the default arena as the number of logical cores, we pin each thread to the logical core that matches its slot number.
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TBB abstracts out threads/OS/hardware so the developers work with TBB tasks instead. So, the current_thread_index() is not supposed to be often used in a sense that thread IDs normally not needed if we use TBB main model of working with tasks. However, for some workloads, for example, typical HPC workload which is regular (i.e., for loops) instead of irregular workloads TBB was designed for, TBB team published examples that assign thread affinities and use current_thread_index() together with other APIs for that.
I suggest to download a free copy of proTBB book from https://www.apress.com/gp/book/9781484243978. From page 360 there:
"
Figure 13-1 shows a simple example of how to use a task_scheduler_observer object to pin threads to cores on Linux. In this example, we use the sched_setaffinity function to set the CPU mask for each thread as it joins the default arena. In Chapter 20, we show an example that assigns affinity using the hwloc software package. In the example in Figure 13-1, we use tbb::this_task_arena::max_concurrency() to find the number of slots in the arena and tbb::this_task_arena::current_thread_index() to find the slot that the calling thread is assigned to. Since we know there will be the same number of slots in the default arena as the number of logical cores, we pin each thread to the logical core that matches its slot number.
