Aufgabe 4: Kontextwechsel

Public Member Functions | Public Attributes | Static Public Attributes | Static Protected Member Functions | Protected Attributes | List of all members
Thread Class Referenceabstract

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). 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 ( )

Constructor Initializes the context using prepareContext with the highest aligned address of the reserved_stack_space array as stack pointer (top of stack).

Note
Remember: Stacks grow to the lower addresses on x86!
Todo:
Implement constructor

Member Function Documentation

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
objectThread to be started
Todo:
Implement Method
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
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
nextPointer 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).
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 KeyboardApplication, and Application.

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