Thread-Safe Superdroplet Shuffling Algorithms

Header file: <libs/superdrops/collisions/shuffle.hpp> [source]

viewd_supers shuffle_supers(const TeamMember &team_member, const viewd_supers supers, const GenRandomPool genpool)

Randomly shuffles the order of super-droplet objects in a view using Fisher-Yates algorithm.

Thread-Safe Kokkos compatible version of Fisher-Yates shuffling algorithm for super-droplets. Shuffling is done in serial (slow!) on single thread per team

Uses only one member of a Kokkos team to randomly shuffle the order of super-droplet objects in the ‘supers’ view using Kokkos compatible rewrite of C++ standard library Fisher-Yates shuffling algorithm. Afterwards synchronizes the team and returns the view of shuffled super-droplets. Uses Kokkos thread safe random number generator from pool.

Parameters:

  • team_member – The Kokkos team member.

  • supers – The view of superdroplets to shuffle.

  • genpool – The random number generator pool.

Returns:

The shuffled view of superdroplets.

inline void device_swap(Superdrop &a, Superdrop &b)

Swaps the values of two super-droplets.

Equivalent to C++98 std::swap but works on device as well as host (gpu compatible).

Note: Involves a copy construction and two assignment operations, which may not be efficient if Superdrop class stores large quantities of data.

Parameters:

  • a – The first super-droplet.

  • b – The second super-droplet.

template<class DeviceType>
inline void fisher_yates_shuffle(URBG<DeviceType> urbg, const auto first, const auto dist)

Shuffles the order of super-droplets in a view.

Randomly shuffles the order of super-droplets using the URBG (Uniform Random Bit Generator) struct (on device). Supers included in shuffle are from iterators in range [first, first+dist] (inclusive), e.g. if first points to the 5th superdroplet and dist=2, then the 5th, 6th and 7th superdroplets will be shuffled amongst each other.

Template Parameters:

DeviceType – The Kokkos device type.

Parameters:

  • urbg – The random number generator.

  • first – iterator/pointer to first element in supers to shuffle

  • dist – number of elements (including first) to shuffle

Returns:

The shuffled view of super-droplets.