Thread Class Reference

The is an object used by the scheduler. More...

#include <thread/thread.h>

Inheritance diagram for Thread:

Collaboration diagram for Thread:

Public Member Functions
	Thread ()
	Constructor Initializes the context using prepareContext with the highest aligned address of the reserved_stack_space array as stack pointer (top of stack). Furthermore, assign each thread a unique id using the global variable idCounter. More...
void	go ()
	Activates the first thread on this CPU. More...
void	resume (Thread *next)
	Switches from the currently running thread to the next one. More...
virtual void	action ()=0
	Method that contains the thread's program code. More...

Public Attributes
const size_t	id
	Unique ID of thread.
volatile bool	kill_flag
	Marker for a dying thread.

Static Public Attributes
static const size_t	STACK_SIZE = 4096
	Stack size for each thread.

Static Protected Member Functions
static void	kickoff (Thread *object)
	Function to start a thread. More...

Protected Attributes
StackPointer	stackpointer
	Current stack pointer of thread for context switch.

Detailed Description

The is an object used by the scheduler.

Constructor & Destructor Documentation

Thread()

Thread::Thread

(

)

Constructor Initializes the context using prepareContext with the highest aligned address of the reserved_stack_space array as stack pointer (top of stack). Furthermore, assign each thread a unique id using the global variable idCounter.

Note

Remember: Stacks grow to the lower addresses on x86!

Todo:

Implement constructor

Member Function Documentation

kickoff()

void Thread::kickoff ( Thread *  object )

staticprotected

Function to start a thread.

For the first activation of a thread, we need a "return address" pointing to a function that will take care of calling C++ virtual methods. For this purpose, we use this kickoff() function.

Activating kickoff

The thread initialization via prepareContext() not only initializes the Stack for the first thread change, but also pushes the address of kickoff() as return address to the stack. Consequently, the first execution of context_switch() will start execution by returning to the beginning of kickoff() .

This kickoff() function simply calls the action() method on the thread passed as parameter and, thus, resolves the virtual C++ method.

Note

As this function is never actually called, but only executed by returning from the threads's initial stack, it may never return. Otherwise garbage values from the stack will be interpreted as return address and the system might crash.

Parameters

object

Thread to be started

Todo:

Implement Method

go()

void Thread::go

(

)

Activates the first thread on this CPU.

Calling the method starts the first thread on the calling CPU. From then on, Thread::resume() must be used all subsequent context switches.

Todo:

Implement Method

resume()

void Thread::resume

(

Thread *

next

)

Switches from the currently running thread to the next one.

The values currently present in the non-scratch (callee-saved) registers will be stored on this thread's stack; the corresponding values belonging to next thread will be loaded (from next's stack).

Parameters

next	Pointer to the next thread.

Todo:

Implement Method

Optional:

To detect stack overflows you can check if the bottom of the stack still contains a predefined value (which was set in constructor).

action()

virtual void Thread::action ( )

pure virtual

Method that contains the thread's program code.

Derived classes are meant to override this method to provide meaningful code to be run in this thread.

Implemented in Application, and KeyboardApplication.

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The documentation for this class was generated from the following files:

• thread/thread.h
• thread/thread.cc