Control threading behavior about ipc-toolkit HOT 3 CLOSED

I added this description here.

from ipc-toolkit.

With multi-threading enabled, it is expected that the results can be non-deterministic because of rounding differences when adding numbers in different orders. We only utilize TBB in the toolkit (excluding experimental CUDA CCD), so to make the results deterministic you can limit TBB's max number of threads to one. The following code shows how to do this:

#include <tbb/global_control.h>
// ...
tbb::global_control thread_limiter(tbb::global_control::max_allowed_parallelism, 1);

As long as this thread_limiter object stays alive, the number of threads will be limited to 1. This example shows the thread limiter stack allocated, so when the object goes out-of-scope, the limit will be released. If you want this limit for the entire length of your program it is best to define it in main or you can define it statically using a std::shared_ptr<tbb::global_control>. For example,

#include <tbb/info.h>
#include <tbb/global_control.h>

static std::shared_ptr<tbb::global_control> thread_limiter;

void set_num_threads(int nthreads)
{
    if (nthreads <= 0) {
        nthreads = tbb::info::default_concurrency();
    } else if (nthreads > tbb::info::default_concurrency()) {
        logger().warn(
            "Attempting to use more threads than available ({:d} > {:d})!",
            nthreads, tbb::info::default_concurrency());
        nthreads = tbb::info::default_concurrency();
    }
    thread_limiter = std::make_shared<tbb::global_control>(
        tbb::global_control::max_allowed_parallelism, nthreads);
}

from ipc-toolkit.

@zfergus: thanks, that's very helpful!

from ipc-toolkit.