Context Switch

Low-Level functionality required for context switching. More...

Classes
struct	StackPointer
	Structure for saving the stack pointer when switching coroutines. More...

Functions
void *	prepareContext (void *tos, void(*kickoff)(void *), void *param1=nullptr)
	Prepares a context for its first activation. More...
void	context_switch (StackPointer &current, StackPointer &next)
	Executes the context switch. More...
void	context_go (StackPointer &next)
	Executes a thread for the very first time. More...

Detailed Description

Low-Level functionality required for context switching.

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Class Documentation

StackPointer

struct StackPointer

Structure for saving the stack pointer when switching coroutines.

Class Members
void *	kernel	Current kernel stack pointer of the thread.

Function Documentation

prepareContext()

void * prepareContext	(	void *	tos,
		void(*)(void *)	kickoff,
		void *	param1 = nullptr
	)

Prepares a context for its first activation.

To allow the execution to start in Thread::kickoff during the first activation, the stack must be initialized such that it contains all the information required. This is, most importantly, the function to be called (typically the respective implementation of Thread::kickoff) and any parameters required by this function.

prepareContext() can be implemented in the high-level programming language C++ (in file context.cc).

Parameters

tos	Pointer to the top of stack (= address of first byte beyond the memory reserved for the stack)
kickoff	Pointer to the Thread::kickoff function
param1	first parameter for Thread::kickoff function

Returns

Pointer to the latest data (which will be popped first) on the prepared stack

context_switch()

void context_switch	(	StackPointer &	current,
		StackPointer &	next
	)

Executes the context switch.

For a clean context switch, the current register values must be stored to the currently active stack and the stack pointer must be stored to the current StackPointer structure. Subsequently, these values must be restored accordingly from the next stack.

This function must be implemented in assembler in the file context.asm. It must be declared as extern "C", as assembler functions are not C++ name mangled.

Parameters

current	Pointer to the structure that the current stack pointer will be stored in
next	Pointer to the structure that the next stack pointer will be read from

context_go()

void context_go

(

StackPointer &

next

)

Executes a thread for the very first time.

For a clean startup, the current register values must be restored accordingly from the next stack.

This function must be implemented in assembler in the file context.asm. It must be declared as extern "C", as assembler functions are not C++ name mangled.

Parameters

next	Pointer to the structure that the next stack pointer will be read from