The aggregation method redefinition

The aggregate function has the following prototype:

int MyScheduler::aggregate(corba_response_t* aggrResp, size_t max_srv,
                            const size_t nb_responses,
                            const corba_response_t* responses)
{
  ...
}

The aggregate method takes 4 arguments:

• corba_response_t* aggrResp: the result of the aggregation has to be set in this argument. aggrResp is an array of corba_server_estimation_t objects.
• size_t max_srv: this argument gives the maximum number of responses to return in aggrResp. This value can be ignored without any risk and it is sometimes useful to ignore it because this parameter is hard-coded in the DIET sources.
• const size_t nb_responses: this argument gives the number of responses in responses.
• const corba_response_t* responses: the responses are stored in this argument. It is an array of corba_response_t which is a CORBA structure containing a CORBA sequence of corba_server_estimation_t.

Two functions are defined to simplify the aggregation of the results:

typedef list<corba_server_estimation_t> ServerList;
ServerList CORBA_to_STL(const corba_response_t* responses, int nb_responses);
void STL_to_CORBA(ServerList &servers, corba_response_t* &aggrResp);

The first function converts the received CORBA sequence into a STL list. This function make the first aggregation of the results by marshaling all the sequences into one.

The second function converts a STL list into a CORBA sequence that can be transfer ed by DIET.

Then, an aggregate function should start by a call to the CORBA_to_STL function. The obtained list can then be sorted/filtered using all the STL list facilities. And to finish, the result list is computed by the STL_to_CORBA function.

Several macros are defined to simplify the sort of a STL list:

SORTFUN(name, metric)
SORTFUN_NB(name, metric, nb)
REV_SORTFUN(name, metric)
REV_SORTFUN_NB(name, metric, nb)

These macros allow the developer to automatically define a sort function using a metric value. For example, to define a sort function using the number of CPUs, the developer just has to declare:

SORTFUN(compfun, NBCPU)

The SORTFUN_NB macro is used for the multi-values metrics (for example the CPU cache for each CPU). The nb value designates which value has to be used to sort the list. The REV_* functions are used to sort in ascending order.

To see all the metrics available for the SORTFUN macro, see Section 9.5.4.

When a sort function has been defined, the developer can use the SORT macro to sort the STL list. For example with our compfun function:

SORT(serverList, compfun);

This call sorts the server STL list in decreasing order of the number of CPU.