Multi-threading

This page is a work in progress. Put everything related to multi-threading here, threads, synchronization, multi-core support, etc.

The Nintendo 3DS offers support for threading through use of SVC calls.

Threads

For Kernel implementation details, see KThread.

Though it is possible to run multi-threaded programs, running those on different cores is not possible "as-is". One core is always dedicated to the OS, hence you will never get 100% of both cores.

Using CloseHandle() with a KThread handle will terminate the specified thread, only if the reference count reaches 0.

Lower priority values give the thread higher priority. For userland apps, priorities between 0x18 and 0x3F are allowed. The priority of the app's main thread seems to be 0x30.

The thread scheduler is cooperative, therefore if a thread takes up all the CPU time (for example if it enters an endless loop), all the other threads that run on the same CPU core won't get a chance to run. The main way of yielding another thread is using an address arbiter.

Usage

CreateThread (svc 0x08)

Definition

Result CreateThread(Handle* thread, func entrypoint, u32 arg, u32 stacktop, s32 threadpriority, s32 processorid);

Configuration

R0=s32 threadpriority
R1=func entrypoint
R2=u32 arg
R3=u32 stacktop
R4=s32 processorid

Result result=R0
Handle* thread=R1

Details The processorid parameter specifies which processor the thread can run on. Non-negative values correspond to a specific CPU. (e.g. 0 for the Appcore and 1 for the Syscore on Old3DS) Special value -1 means all CPUs, and -2 means the default CPU for the process (Read from the Exheader, usually 0 for applications, 1 for system services). Games usually create threads using -2.

With the Old3DS kernel, the s32 processorid must be <=2.

With the New3DS kernel: processorid must be <= <total cores(MPCore "SCU Configuration Register" CPU number value + 1)>. When processorid==0x2 and the process is not an APPLICATION mem-region process, exheader kernel-flags bitmask 0x2000 must be set otherwise error 0xD9001BEA is returned. When processorid==0x3 and the process is not an APPLICATION mem-region process, error 0xD9001BEA is returned. These are the only restriction checks done by the kernel for processorid.

The thread priority value must be in the following range: 0x0..0x3F.

The stacktop must be aligned to 0x8-bytes, otherwise when not aligned to 0x8-bytes the ARM11 kernel clears the low 3-bits of the stacktop address.

The input address used for Entrypoint_Param and StackTop are normally the same, however these can be arbitrary. For the main thread the Entrypoint_Param is value 0.

ExitThread (svc 0x09)

Definition

void ExitThread(void);

SleepThread (svc 0x0A)

Definition

void SleepThread(s64 nanoseconds);

GetThreadPriority (svc 0x0B)

Definition

Result GetThreadPriority(s32* priority, Handle thread);

asm

.global svcGetThreadPriority
.type svcGetThreadPriority, %function
svcGetThreadPriority:
	str r0, [sp, #-0x4]!
	svc 0x0B
	ldr r3, [sp], #4
	str r1, [r3]
	bx  lr

SetThreadPriority (svc 0x0C)

Definition

Result SetThreadPriority(Handle thread, s32 priority);

OpenThread (svc 0x34)

Definition

Result OpenThread(Handle* thread, Handle process, u32 threadId);

GetProcessIdOfThread (svc 0x36)

Definition

Result GetProcessIdOfThread(u32* processId, Handle thread);

GetThreadId (svc 0x37)

Definition

Result GetThreadId(u32* threadId, Handle thread);

GetThreadInfo (svc 0x2C)

Definition

Result GetThreadInfo(s64* out, Handle thread, ThreadInfoType type);

ThreadInfoType value	Description
?	?

GetThreadContext (svc 0x3B)

Definition

Result GetThreadContext(ThreadContext* context, Handle thread);

Details Stubbed?

Core affinity

GetThreadAffinityMask (svc 0x0D)

Definition

Result GetThreadAffinityMask(u8* affinitymask, Handle thread, s32 processorcount);

SetThreadAffinityMask (svc 0x0E)

Definition

Result SetThreadAffinityMask(Handle thread, u8* affinitymask, s32 processorcount);

GetThreadIdealProcessor (svc 0x0F)

Definition

Result GetThreadIdealProcessor(s32* processorid, Handle thread);

Synchronization

Most synchronization systems seem to have both a "normal" and "light-weight" version

Mutex (normal)

For Kernel implementation details, see KMutex

CreateMutex

/!\ It seems that the mutex will not be available once the thread that created it is destroyed

CriticalSection::Initialize

Same thread ownership as a mutex ?

Light Semaphore ?

Does it exist ?