hpx/collectives/reduce.hpp

See Public API for a list of names and headers that are part of the public HPX API.

namespace hpx
namespace collectives

Functions

template<typename T, typename F>
hpx::future<std::decay_t<T>> reduce_here(char const *basename, T &&result, F &&op, num_sites_arg num_sites = num_sites_arg(), this_site_arg this_site = this_site_arg(), generation_arg generation = generation_arg())

Reduce a set of values from different call sites

This function receives a set of values from all call sites operating on the given base name.

Return

This function returns a future holding a vector with all values send by all participating sites. It will become ready once the all_reduce operation has been completed.

Parameters

  • basename: The base name identifying the all_reduce operation

  • local_result: A value to reduce on the central reduction point from this call site.

  • op: Reduction operation to apply to all values supplied from all participating sites

  • num_sites: The number of participating sites (default: all localities).

  • generation: The generational counter identifying the sequence number of the all_reduce operation performed on the given base name. This is optional and needs to be supplied only if the all_reduce operation on the given base name has to be performed more than once.

  • this_site: The sequence number of this invocation (usually the locality id). This value is optional and defaults to whatever hpx::get_locality_id() returns.

template<typename T, typename F>
hpx::future<decay_t<T>> reduce_here(communicator comm, T &&local_result, F &&op, this_site_arg this_site = this_site_arg())

Reduce a set of values from different call sites

This function receives a set of values that are the result of applying a given operator on values supplied from all call sites operating on the given base name.

Return

This function returns a future holding a value calculated based on the values send by all participating sites. It will become ready once the all_reduce operation has been completed.

Parameters

  • comm: A communicator object returned from create_communicator

  • local_result: A value to reduce on the root_site from this call site.

  • op: Reduction operation to apply to all values supplied from all participating sites

  • this_site: The sequence number of this invocation (usually the locality id). This value is optional and defaults to whatever hpx::get_locality_id() returns.

template<typename T, typename F>
hpx::future<void> reduce_there(char const *basename, T &&result, this_site_arg this_site = this_site_arg(), generation_arg generation = generation_arg(), root_site_arg root_site = root_site_arg())

Reduce a given value at the given call site

This function transmits the value given by result to a central reduce site (where the corresponding reduce_here is executed)

Return

This function returns a future<void>. It will become ready once the reduction operation has been completed.

Parameters

  • basename: The base name identifying the reduction operation

  • result: A future referring to the value to transmit to the central reduction point from this call site.

  • generation: The generational counter identifying the sequence number of the reduction operation performed on the given base name. This is optional and needs to be supplied only if the reduction operation on the given base name has to be performed more than once.

  • this_site: The sequence number of this invocation (usually the locality id). This value is optional and defaults to whatever hpx::get_locality_id() returns.

  • root_site: The sequence number of the central reduction point (usually the locality id). This value is optional and defaults to 0.

template<typename T>
hpx::future<void> reduce_there(communicator comm, T &&local_result, this_site_arg this_site = this_site_arg())

Reduce a given value at the given call site

This function transmits the value given by result to a central reduce site (where the corresponding reduce_here is executed)

Return

This function returns a future holding a value calculated based on the values send by all participating sites. It will become ready once the all_reduce operation has been completed.

Parameters

  • comm: A communicator object returned from create_communicator

  • local_result: A value to reduce on the central reduction point from this call site.

  • this_site: The sequence number of this invocation (usually the locality id). This value is optional and defaults to whatever hpx::get_locality_id() returns.