= Multicore apps =

The average number of cores per PC will increase over the next few years,
possibly at a faster rate than the average amount of available RAM.

Depending on your application and project,
it may be desirable to develop a multi-thread application.
Possible reasons to do this:

 * Your application's memory footprint is large enough that, on some PCs, there's not enough RAM to run a separate copy of the app on each CPU.
 * You want to reduce the turnaround time of your jobs (either because of human factors, or to reduce server occupancy).

You may be able to use OpenCL, MPI, OpenMP,
[http://blogs.nvidia.com/2011/06/cuda-now-available-for-multiple-x86-processors/ CUDA],
languages like Titanium or Cilk,
or libraries of multi-threaded numerical "kernels", to develop a multi-threaded app.

== Initialization ==

You will need to use
[BasicApi#Parallelapps the appropriate initialization function].

== Waiting for children ==

If your application uses multiple process,
the parent process must always wait for children to exit before exiting itself.

== Thread priorities ==

You should set the priority of new threads to that of the main thread.
{{{
#ifdef MSVC
#define getThreadPriority() GetThreadPriority(GetCurrentThread())
#define setThreadPriority(num) SetThreadPriority(GetCurrentThread(), num)
#else
#include <sys/resource.h>
#define getThreadPriority() getpriority(PRIO_PROCESS, 0)
#define setThreadPriority(num) nice(num)
#endif
}}}
getThreadPriority() is called before forking (by OpenMP in AQUA's case),
and setThreadPriority() is then called by each worker thread.

== Specifying a plan class ==

Multicore apps must the [AppPlan plan class] mechanism to specify their properties.
You may be able to use the [AppPlan predefined "mt" class].
Otherwise you must specify your own,
using either [AppPlanSpec XML] or [PlanClassFunc C++].