Multithreading question

BlitzMax Forums/BlitzMax Programming/Multithreading question

JBR	(Posted 2010) [#1]

Is there a way to limit the number of cores used within the program.

Just for testing - one core vs two cores etc.

I could use the set affinity but it's a hastle.

Thanks
Jim

ImaginaryHuman

(Posted 2010) [#2]

It's kinda up to the o/s to distribute threads across cores... might be some specific api calls you can make though?

BlitzSupport

(Posted 2010) [#3]

This will let you set processor affinity programmatically (on Windows)...


Extern "win32"

	Const CREATE_SUSPENDED=$4
	Const STACK_SIZE_PARAM_IS_A_RESERVATION=$10000
	
	Const INFINITE=$ffffffff
	Const WAIT_ABANDONED=$80
	Const WAIT_OBJECT_0=$0
	Const WAIT_TIMEOUT=$102
	Const WAIT_FAILED=$ffffffff
	
	Const THREAD_MODE_BACKGROUND_BEGIN = $00010000
	Const THREAD_MODE_BACKGROUND_END = $00020000
	Const THREAD_PRIORITY_ABOVE_NORMAL = 1
	Const THREAD_PRIORITY_BELOW_NORMAL = -1
	Const THREAD_PRIORITY_HIGHEST = 2
	Const THREAD_PRIORITY_IDLE = -15
	Const THREAD_PRIORITY_LOWEST = -2
	Const THREAD_PRIORITY_NORMAL = 0
	Const THREAD_PRIORITY_TIME_CRITICAL = 15

	Function ResumeThread( thread )
	Function SuspendThread( thread )
	Function CloseThread( thread )
	Function WaitForSingleObject( handle,timeout )
	Function GetThreadPriority (thread)
	Function SetThreadPriority (thread, priority)
	Function GetCurrentThread ()

	Const PROCESS_SET_INFORMATION = $200
	
	Function GetCurrentProcessId ()
	Function OpenProcess (desiredaccess, inherithandle, processid)
	Function SetProcessAffinityMask (processhandle, processaffinitymask)
	
End Extern





' -------------------------------------------------------------------------
' Get process and open process handle...
' -------------------------------------------------------------------------

Local proc:Int = GetCurrentProcessId ()
Local handle:Int = OpenProcess (PROCESS_SET_INFORMATION, 0, proc)

' -------------------------------------------------------------------------
' Force process to CPU...
' -------------------------------------------------------------------------

' First CPU:
SetProcessAffinityMask (handle, %00000000000000000000000000000001)

' Second CPU:
'SetProcessAffinityMask (handle, %00000000000000000000000000000010)

' First 2 CPUs (default on dual-core):
'SetProcessAffinityMask (handle, %00000000000000000000000000000011)
	
' -------------------------------------------------------------------------

Print "Open task manager and view process affinity (right click app, Set Affinity)..."

Repeat

	Delay 100
	
Until KeyHit (KEY_ESCAPE)

End


Rem

<a href="http://msdn.microsoft.com/en-us/library/ms686277(VS.85).aspx" target="_blank">http://msdn.microsoft.com/en-us/library/ms686277(VS.85).aspx</a>

THREAD_MODE_BACKGROUND_BEGIN = $00010000
Begin background processing mode. The system lowers the resource scheduling priorities of the thread so that it can perform background work without significantly affecting activity in the foreground.
This value can be specified only if hThread is a handle to the current thread. The function fails if the thread is already in background processing mode.
Windows Server 2003 and Windows XP/2000:  This value is not supported.

THREAD_MODE_BACKGROUND_END = $00020000
End background processing mode. The system restores the resource scheduling priorities of the thread as they were before the thread entered background processing mode.
This value can be specified only if hThread is a handle to the current thread. The function fails if the thread is not in background processing mode.
Windows Server 2003 and Windows XP/2000:  This value is not supported.

THREAD_PRIORITY_ABOVE_NORMAL = 1
Priority 1 point above the priority class.

THREAD_PRIORITY_BELOW_NORMAL = -1
Priority 1 point below the priority class.

THREAD_PRIORITY_HIGHEST = 2
Priority 2 points above the priority class.

THREAD_PRIORITY_IDLE = -15
Base priority of 1 for IDLE_PRIORITY_CLASS, BELOW_NORMAL_PRIORITY_CLASS, NORMAL_PRIORITY_CLASS, ABOVE_NORMAL_PRIORITY_CLASS, or HIGH_PRIORITY_CLASS processes, and a base priority of 16 for REALTIME_PRIORITY_CLASS processes.

THREAD_PRIORITY_LOWEST = -2
Priority 2 points below the priority class.

THREAD_PRIORITY_NORMAL = 0
Normal priority for the priority class.

THREAD_PRIORITY_TIME_CRITICAL = 15
Base priority of 15 for IDLE_PRIORITY_CLASS, BELOW_NORMAL_PRIORITY_CLASS, NORMAL_PRIORITY_CLASS, ABOVE_NORMAL_PRIORITY_CLASS, or HIGH_PRIORITY_CLASS processes, and a base priority of 31 for REALTIME_PRIORITY_CLASS processes.

If the thread has the REALTIME_PRIORITY_CLASS base class, this parameter can also be -7, -6, -5, -4, -3, 3, 4, 5, or 6.

End Rem

JBR	(Posted 2010) [#4]

Many Thanks
Jim

JBR	(Posted 2010) [#5]

What does Extern "win32" do?

Where are the functions from?

Jim

Forgot to ask, I've got the i7 quad core and it comes with hyperthreading which shows up as 8 cores. 0 to 7. What are the numbers of the real cores?

Last edited 2010

byo	(Posted 2010) [#6]

It's there to show Blitzmax you're going to declare and use Windows API functions from DLLs that comes with Windows.

Google "Windows API" to learn more about the functions used.

BlitzSupport

(Posted 2010) [#7]

Yeah, you can also Google msdn SetProcessAffinityMask (or any of the other functions) to find the docs for these Windows calls.

In terms of finding the number of 'real' cores, it's possible, but takes quite a bit of effort -- and for what? Windows is still going to treat it as an 8-core processor no matter what!

You could probably use the GetNumaProcessorNodeEx function to work out which of the 8 cores relate to each 'real' core, but I don't think it's worth bothering with, since the information is (practically) useless.

Scaremonger

(Posted 2014) [#8]

Cheers James.. :)

ImaginaryHuman

(Posted 2014) [#9]

That was a slightly overdue thankyou, lol