HashedDist

Usage

use HashedDist;

class Hashed

The Hashed distribution maps an associative domain and its array to a set of target locales. Each index (or key) in the domain is mapped to a locale based upon its value. When constructing a Hashed distribution, you can optionally provide a mapper function or function object to compute the destination locale for each index.

The mapper provided can be a class, record, or first class function. When called, it will be passed the index and the targetLocales array that the Hashed distribution was initialized with. For example, the following record declares a custom mapper:

record CustomMapper {
  proc this(ind:string, targetLocs: [?D] locale) : D.idxType {
    const numlocs = targetLocs.domain.size;
    // use the first digit of the string to choose the destination locale
    var byte: int = ind.byte(1);
    return byte % numlocs;
  }
}

If a custom mapper is not provided, a default mapper will be used. The default mapper computes the target locale based upon a hash of the index.

Note

Hashed is not yet interface stable.

Example

var D: domain(string) dmapped Hashed(idxType=string);
// Now D is a distributed associative domain (set) of strings
D += "one";
D += "two";

var A: [D] int;
// Now A is a distributed associative array (map) from string to int
forall a in A do
  a = a.locale.id;

forall (key, value) in zip(D, A) {
  writeln(key, " -> ", value);
}

Initializer Arguments

The Hashed domain map initializer is defined as follows:

proc init(type idxType,
          mapper:?t = new DefaultMapper(),
          targetLocales: [] locale = Locales)