More intelligent std::async decision to make new thread

[Ko Stoffelen <k dot stoffelen at cs dot ru dot nl>]

Hi,

I have a bunch of tasks that I'd like to execute in parallel as fast as
possible. I'm using std::async for this purpose, without a launch
policy, which is then std::launch::async | std::launch::deferred by
default. Now if I understand correctly, the C++ standard leaves it to
the implementation how it should handle this launch policy. libstdc++
always first tries to create a new thread and only if that raises an
exception, the task is deferred.

https://gcc.gnu.org/onlinedocs/gcc-6.1.0/libstdc++/api/a01298_source.html#l01716

In practice, this could imply that I'm running >100 threads on 4 cores
and the OS is only switching tasks all the time, actually delaying the
computation. Is it possible to make a more intelligent decision at
runtime, based on, e.g., the number of cores or the current CPU load?

Thanks,

Ko

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