Scheduler Class Reference

The scheduler plans the threads' execution order and, from this, selects the next thread to be running. More...

#include <scheduler.h>

Collaboration diagram for Scheduler:

Public Member Functions
void	schedule ()
	Start scheduling.
void	ready (Thread *that)
	Include a thread in scheduling decisions.
void	exit ()
	(Self-)termination of the calling thread.
void	kill (Thread *that)
	Kills the passed thread.
void	resume (bool ready=true)
	Issue a thread change.
Thread *	active ()
	return the active thread from the dispatcher
bool	isActive (const Thread *thread, unsigned int *cpu=nullptr)
	Check if thread is currently active.
bool	isEmpty () const
	Checks whether the ready queue is empty.
void	setIdle (IdleThread *that)
	Set the idle thread for the executing CPU.
bool	isIdle (int cpu)
	Check wether the specified CPU core is idle.

Private Member Functions
Thread *	getNext ()
	Helper to retrieve next Thread.

Private Attributes
Dispatcher	dispatcher
	a Dispatcher object, providing the low level context switching routines.
Queue< Thread >	readylist
	List of threads, ready to be run.
IdleThread *	idleThread [Core::MAX]
	Idle thread.

Detailed Description

The scheduler plans the threads' execution order and, from this, selects the next thread to be running.

The scheduler manages the ready queue (a private Queue object), that is the list of threads that are ready to execute. The scheduler arranges threads in a FIFO order, that is, when a thread is set ready, it will be appended to the end of the queue, while threads to be executed are taken from the front of the queue.

Member Function Documentation

exit()

void Scheduler::exit

(

)

(Self-)termination of the calling thread.

This method can be used by a thread to exit itself. The calling thread will not be appended to the ready queue; a reschedule will be issued.

getNext()

Thread * Scheduler::getNext ( )

private

Helper to retrieve next Thread.

Returns

pointer of next thread

isActive()

bool Scheduler::isActive	(	const Thread *	thread,
		unsigned int *	cpu = nullptr )

Check if thread is currently active.

Parameters

thread	Pointer to the thread in question
getCpuId	If not null, the core that the thread is running on, if applicable

Returns

true if currently running, false otherwise

isIdle()

bool Scheduler::isIdle

(

int

cpu

)

Check wether the specified CPU core is idle.

Parameters

cpu	CPU core to check

kill()

void Scheduler::kill

(

Thread *

that

)

Kills the passed thread.

This method is used to kill the Thread that. For OOStuBS, it is sufficient to remove that from the ready queue and, thereby, exclude the thread from scheduling. For MPStuBS, a simple removal is not sufficient, as the thread might currently be running on another CPU core. In this case, the thread needs to be marked as dying (a flag checked by resume prior to enqueuing into the ready queue)

and the executing CPU core needs to be notified.

Note: The thread should be able to kill itself.

ready()

void Scheduler::ready

(

Thread *

that

)

Include a thread in scheduling decisions.

This method will register a thread for scheduling. It will be appended to the ready queue and dispatched once its time has come.

Parameters

that	Thread to be scheduled

resume()

void Scheduler::resume

(

bool

ready = true

)

Issue a thread change.

This method issues the change of the currently active thread without requiring the calling thread to be aware of the other threads. Scheduling decisions, i.e. which thread will be run next, are made by the scheduler itself with the knowledge of the currently ready threads. The currently active thread is appended to the end of the queue; the first thread in the queue will be activated (to implement the FIFO policy).

Parameters

ready

If false, the currently active thread will not be enqueued for scheduling again.

schedule()

void Scheduler::schedule

(

)

Start scheduling.

This method starts the scheduling by removing the first thread from the ready queue and activating it. MPStuBS needs to call this method once for every CPU core to dispatch the first thread.

setIdle()

void Scheduler::setIdle

(

IdleThread *

that

)

Set the idle thread for the executing CPU.

Parameters

[in]

that

the idle thread to use for the executing CPU

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

• thread/scheduler.h
• thread/scheduler.cc