Thread Class Reference

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

#include <thread.h>

Inheritance diagram for Thread:

Collaboration diagram for Thread:

Public Member Functions
	Thread (void *tos)
	Constructor Initializes the context using prepareContext with the given stack space.
void	go ()
	Activates the first thread on this CPU.
void	resume (Thread *next)
	Switches from the currently running thread to the next one.
virtual void	action ()=0
	Method that contains the thread's program code.
Waitingroom *	getWaitingroom () const
	Returns the Waitingroom in which the thread is currently waiting.
void	setWaitingroom (Waitingroom *w)
	Marks the thread as waiting for an event in Waitingroom w.

Public Attributes
volatile bool	kill_flag
	Marker for a dying thread.

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

Protected Attributes
Context	context
	Context of the thread, used for saving and restoring the register values when context switching.

Private Attributes
Thread *	queue_link [1]
	pointer to the next element of the readylist
Waitingroom *	waitingroom = nullptr
	Pointer to waiting room.

Friends
class	Queue< Thread >
class	Waitingroom

Detailed Description

The Thread is an object used by the scheduler.

Constructor & Destructor Documentation

Thread()

Thread::Thread ( void * tos )

explicit

Constructor Initializes the context using prepareContext with the given stack space.

Parameters

tos	the top of stack, highest address of some memory block that should be used as stack (remember stacks grow to the lower addresses on x86).

Member Function Documentation

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 IdleThread, Application, and KeyboardApplication.

getWaitingroom()

Waitingroom * Thread::getWaitingroom ( ) const

inline

Returns the Waitingroom in which the thread is currently waiting.

Returns 0 in case the thread does not waiting in any Waitingroom, that is, the thread is either running, in the ready list, already terminated or not yet registered at the scheduler.

Returns

Pointer to a Waitingroom in which the thread is waiting, or nullptr.

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.

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 context 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 co-routine'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

resume()

void Thread::resume

(

Thread *

next

)

Switches from the currently running thread to the next one.

The values currently present in the callee-saved registers will be stored in this threads context-structure, the corresponding values belonging to next thread will be loaded.

Parameters

next	Pointer to the next thread.

setWaitingroom()

void Thread::setWaitingroom ( Waitingroom * w )

inline

Marks the thread as waiting for an event in Waitingroom w.

Parameters

w	The Waitingroom this thread is waiting in.

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

• thread/thread.h
• thread/thread.cc