Add global start/stop API for performance counters

[hkaiser]

Add global start/stop API for performance counters allowing to explicitly instrument application code.

[hkaiser]

We will add 4 new API functions:

hpx::start_active_counters(hpx::error_code& ec = throws);
hpx::stop_active_counters(hpx::error_code& ec = throws);
hpx::reset_active_counters(hpx::error_code& ec = throws);
hpx::evaluate_active_counters(bool reset = false, char const* description = 0, 
    hpx::error_code& ec = throws);

This should allow for arbitrary application specific instrumentation. These API functions will refer to the counters which are specified on the command lines using the command line option --hpx:print-counter.

If no counters are being specified on the command line these functions will have no effect.

[pagrubel]

And if none of these API's are used the counters will be active for the entire program, right?

[hkaiser]

Yes, same as before.

[hkaiser]

This has been fixed by dffb281