#14 thread priority

[Steven Van Ingelgem]

Is it possible to add some kind of priority to threads?
I know both linux and windows support setting the thread priority, so might be a good idea to add it (and I also need it ;)).

Greetz

[Davis]

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I considered adding this feature a few months ago but ended up not doing so. It doesn't seem like this is something that can be even remotely portable. For instance POSIX threads doesn't *really* supply any API to deal with setting a thread's priority. Sorta, it does give some things but their exact behavior is "implementation defined" so in effect it does not provide support.

What are you trying to do specifically?

[Steven Van Ingelgem]

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At the moment I am creating some program which needs to calculate on my computer for like 66 seconds before all possible routings have been found (and there is not a really less cpu consuming way to do it). So I thought like 'put a mutex & lock it till initial calculations are done', put this initial calculations inside a low priority thread. Because the user doesn't do anything (most of the time for like 2 minutes before the program is being used because then the game is being started). But I can't do it in a normal thread because that would consume all the possible cpu power...

windows: SetThreadPriority
linux: (thanks to wxWidgets: threadpsx.cpp @ 1237)
#ifdef HAVE_THREAD_PRIORITY_FUNCTIONS
#if defined(__LINUX__)
// On Linux, pthread_setschedparam with SCHED_OTHER does not allow
// a priority other than 0. Instead, we use the BSD setpriority
// which alllows us to set a 'nice' value between 20 to -20. Only
// super user can set a value less than zero (more negative yields
// higher priority). setpriority set the static priority of a
// process, but this is OK since Linux is configured as a thread
// per process.
//
// FIXME this is not true for 2.6!!

// map wx priorites WXTHREAD_MIN_PRIORITY..WXTHREAD_MAX_PRIORITY
// to Unix priorities 20..-20
if ( setpriority(PRIO_PROCESS, 0, -(2*prio)/5 + 20) == -1 )
{
wxLogError(_("Failed to set thread priority %d."), prio);
}
#else // __LINUX__
{
struct sched_param sparam;
sparam.sched_priority = prio;

if ( pthread_setschedparam(m_internal->GetId(),
SCHED_OTHER, &sparam) != 0 )
{
wxLogError(_("Failed to set thread priority %d."), prio);
}
}
#endif // __LINUX__
#endif // HAVE_THREAD_PRIORITY_FUNCTIONS

Best to check first if the thread is running...

[Davis]

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Have you tried doing this with all your threads being normal priority? I would expect that it would work just fine. The OS should schedule the threads in a way that prevents thread starvation.