RFC: fetchgroup api

["Frank Ch. Eigler" <fche@xxxxxxxxxx>]

Hi -

I have finally made some progress on the "fetchgroup" api extension
that we had talked about a year ago and then some [1].  It's starting
to come together, and am looking for feedback on design or smaller
issues.

The work is all on git://sourceware.org/git/pcpfans.git fche/fetchgroup .

The core implementation is in libpcp/src/fetchgroup.c; a man page in
man/man3/pmfetchgroup.3 with a sample program (below); and adapts
src/pmmgr and src/pmclient to the api.  QA and fixes are coming.  The
man page would be a good one to start from.  I'd be happy to explain
further.



#include <pcp/pmapi.h>
#include <assert.h>
#include <stdio.h>

int main () {
    pmFG fg;
    pmAtomValue v, v2;
    int sts, i;
    int c = pmNewContext(PM_CONTEXT_HOST, "local:");
    assert (c >= 0);
    sts = pmCreateFetchGroup(&fg);
    assert (sts == 0);
    sts = pmExtendFetchGroup_item(fg, "kernel.all.load", "1 minute",
                                  NULL, &v, PM_TYPE_FLOAT, NULL);
    assert (sts == 0);
    sts = pmExtendFetchGroup_item(fg, "kernel.all.idletime", NULL,
                                  "hour", &v2, PM_TYPE_DOUBLE, NULL);
    assert (sts == 0);
    for (i=0; i<10; i++) {
        sts = pmFetchGroup(fg);
        assert (sts == 0);
        printf ("1-minute load: %f; idletime: %f h\n", v.f, v2.d);
        sleep (1);
    }
    sts = pmDestroyFetchGroup(fg);
    assert (sts == 0);
    pmDestroyContext (c);
}



[1] http://oss.sgi.com/archives/pcp/2014-10/msg00029.html


- FChE