rapidsmpf::Tag Class Reference

A tag used for identifying messages in a communication operation. More...

#include <communicator.hpp>

Public Types
using	StorageT = std::int32_t
	The physical data type to store the tag.

Public Member Functions
constexpr	Tag (OpID const op, StageID const stage)
	Constructs a tag. More...
constexpr	operator StorageT () const noexcept
	Returns the int32 view of the tag. More...
constexpr OpID	op () const noexcept
	Extracts the operation ID from the tag. More...
constexpr StageID	stage () const noexcept
	Extracts the stage ID from the tag. More...

Static Public Member Functions
static constexpr std::size_t	bit_length () noexcept
	Returns the max number of bits used for the tag. More...
static constexpr StorageT	max_value () noexcept
	Returns the max value of the tag. More...

Static Public Attributes
static constexpr int	stage_id_bits {3}
	Number of bits for the stage ID.
static constexpr StorageT	stage_id_mask {(1 << stage_id_bits) - 1}
	Mask for the stage ID.
static constexpr int	op_id_bits {20}
	Number of bits for the operation ID.
static constexpr StorageT	op_id_mask
	Mask for the operation ID. More...

Detailed Description

A tag used for identifying messages in a communication operation.

The tag is a 32-bit integer, with the following layout (low bits to high bits left-to-right)

bits   | 012       | 34567 01234567 0123456 | 7 01234567
       |           |                        |
value  | stage (3) | operation (20)         | empty (9)
       |           |                        |

{}

The restriction of 23 used bits comes from empirical MPI implementation limits for MPI_TAG_UB. For example, when using UCX as a transport layer, OpenMPI is restricted to 2^23 distinct tags.

All messages in rapidsmpf over the same Communicator are disambiguated by Tags. A message sent with a given Tag can only be matched by a receive with a matching Tag.

In the same way, collective operations over a Communicator are disambiguated by an OpID: two different collectives with different OpIDs will not interfere.

Due to implementation restrictions, we are limited in the number of distinct tags we can use (the Tag constructor checks for overflow but not reuse). In particular, we support at most 2^20 distinct OpIDs, corresponding to 2^20 distinct collectives running simultaneously.

Definition at line 83 of file communicator.hpp.

Constructor & Destructor Documentation

Tag()

constexpr rapidsmpf::Tag::Tag ( OpID const  op, StageID const  stage  )

inlineconstexpr

Constructs a tag.

Exceptions

std::overflow_error

If either the op or stage values are negative or too large.

Parameters

op	The operation ID
stage	The stage ID

Definition at line 114 of file communicator.hpp.

Member Function Documentation

bit_length()

static constexpr std::size_t rapidsmpf::Tag::bit_length ( )

inlinestaticconstexprnoexcept

Returns the max number of bits used for the tag.

Returns

bit length

Definition at line 132 of file communicator.hpp.

max_value()

static constexpr StorageT rapidsmpf::Tag::max_value ( )

inlinestaticconstexprnoexcept

Returns the max value of the tag.

Returns

max value

Definition at line 140 of file communicator.hpp.

op()

constexpr OpID rapidsmpf::Tag::op ( ) const

inlineconstexprnoexcept

Extracts the operation ID from the tag.

Returns

The operation ID

Definition at line 156 of file communicator.hpp.

operator StorageT()

constexpr rapidsmpf::Tag::operator StorageT ( ) const

inlineconstexprnoexcept

Returns the int32 view of the tag.

Returns

int32 view of the tag

Definition at line 148 of file communicator.hpp.

stage()

constexpr StageID rapidsmpf::Tag::stage ( ) const

inlineconstexprnoexcept

Extracts the stage ID from the tag.

Returns

The stage ID

Definition at line 164 of file communicator.hpp.

Member Data Documentation

op_id_mask

constexpr StorageT rapidsmpf::Tag::op_id_mask

staticconstexpr

Initial value:

{
        ((1 << (op_id_bits + stage_id_bits)) - 1) ^ stage_id_mask
    }

Mask for the operation ID.

Definition at line 101 of file communicator.hpp.

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The documentation for this class was generated from the following file:

• /__w/rapidsmpf/rapidsmpf/cpp/include/rapidsmpf/communicator/communicator.hpp