Template:ElementTypeCommunication

When a variable is assigned to another, depending on where each variable is allocated to, there may be communication required to achieve this assignment. Table \ref{tab:eltypecomm} details the communication rules in the assignment \emph{assignmed variable := assigning variable}. If the communication is issued from MPMD programming style then this will be one sided. The default communication listed here is guaranteed to be safe, which may result in a small performance hit.

Assigned Variable	Assigning Variable	Semantics
multiple[]	multiple[]	local assignment
single[on[i]]	multiple[]	local assignment on process i
multiple[]	single[on[i]]	broadcast from process i
single[on[i]]	single[on[i]]	local assignment where i==i
single[on[i]]	single[on[j]]	communication from j to i where i!=j

Communication Example

var a:Int;
var b:Int :: allocated[single[on[2]]];
var p;
par p from 0 to 3
{
   if (p==2) b:=p;
   a:=b;
};

This code will result in a onesided broadcast (due to being written MPMD style in par loop) where process 2 will broadcast its value of b to all other processes who will write it into a. As already noted, in absence of allocation information the default of allocating to all processes is used. In this example the variable a can be assumed to additionally have the type allocated[multiple].