Function async_test

Tests/GPU/Vector/main.cpp:60–98

}

void async_test()
{
    {
        int N = 32*10;  // 10 warps. Arbitrarily chosen.

        Gpu::AsyncVector<Real> vec(N, 0.0);
        auto ptr = vec.dataPtr();

        // Compute-bound test. Should take some time.
        amrex::ParallelFor(N, [=] AMREX_GPU_DEVICE (int n) noexcept
        {
            Real y = ptr[n];
            Real x = 1.0;
            for (int n = 0; n < 20; ++n) {
                Real dx = -(x*x-y) / (2.*x);
                x += dx;
            }
            ptr[n] = x;

            if (n == 0)
#ifdef AMREX_USE_GPU
                { AMREX_DEVICE_PRINTF(" Answer = %1.16f -- should print second.\n", ptr[n]); }
#else
                { std::cout << "Answer = " << ptr[n] << " -- should print first." << '\n'; }
#endif

        });
    }

    // Async Vector now out of scope. Still completes correctly.

#ifdef AMREX_USE_GPU
    amrex::Print() << "Async Syncing -- should print first." << '\n';
#else
    amrex::Print() << "Async Syncing -- should print second." << '\n';
#endif

    Gpu::Device::streamSynchronize();
}

int main (int argc, char* argv[])
{