Difference between revisions of "Template:ElementTypeCommunication"
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| − | This code will result in each process reading the value of ''b'' from process 2 and then writing this 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]''. | + | This code will result in each process reading the value of ''b'' from process 2 and then writing this 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]''. Note that communication groups are the same as multiple in this context and share the same semantics. All variables marked multiple are private to their containing process. |
Revision as of 12:51, 18 October 2016
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[] | individual processes write values to process i |
| multiple[] | single[on[i]] | individual processes read values 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;
sync;
};
This code will result in each process reading the value of b from process 2 and then writing this 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]. Note that communication groups are the same as multiple in this context and share the same semantics. All variables marked multiple are private to their containing process.
