genode/base/include/util/fifo.h
Martin Stein b7c1404fbf base & core: Use FIFO to queue RM faulters.
By now RM faulters are hold in a LIFO. Thus a starvation problem
occurs on managed dataspaces when multiple threads throw pagefaults
continuously.
2012-11-23 12:20:26 +01:00

151 lines
2.8 KiB
C++

/*
* \brief Queue with first-in first-out semantics
* \author Norman Feske
* \date 2008-08-15
*/
/*
* Copyright (C) 2008-2012 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU General Public License version 2.
*/
#ifndef _INCLUDE__UTIL__FIFO_H_
#define _INCLUDE__UTIL__FIFO_H_
namespace Genode {
/*
* \param QT queue element type
*/
template <typename QT>
class Fifo
{
public:
class Element
{
protected:
friend class Fifo;
QT *_next;
bool _is_enqueued;
public:
Element(): _next(0), _is_enqueued(false) { }
/**
* Return true is fifo element is enqueued in a fifo
*/
bool is_enqueued() { return _is_enqueued; }
/**
* Return next element in queue
*/
QT *next() const { return _next; }
};
private:
QT *_head; /* oldest element */
Element *_tail; /* newest element */
public:
/**
* Return true if queue is empty
*/
bool empty() { return _tail == 0; }
/**
* Constructor
*
* Start with an empty list.
*/
Fifo(): _head(0), _tail(0) { }
/**
* Return first queue element
*/
QT *head() const { return _head; }
/**
* Remove element explicitely from queue
*/
void remove(QT *qe)
{
if (empty()) return;
/* if specified element is the first of the queue */
if (qe == _head) {
_head = qe->Element::_next;
if (!_head) _tail = 0;
}
else {
/* search specified element in the queue */
Element *e = _head;
while (e->_next && (e->_next != qe))
e = e->_next;
/* element is not member of the queue */
if (!e->_next) return;
/* e->_next is the element to remove, skip it in list */
e->Element::_next = e->Element::_next->Element::_next;
if (!e->Element::_next) _tail = e;
}
qe->Element::_next = 0;
qe->Element::_is_enqueued = 0;
}
/**
* Attach element at the end of the queue
*/
void enqueue(QT *e)
{
e->Fifo::Element::_next = 0;
e->Fifo::Element::_is_enqueued = true;
if (empty()) {
_tail = _head = e;
return;
}
_tail->Fifo::Element::_next = e;
_tail = e;
}
/**
* Obtain head element of the queue and remove element from queue
*
* \return head element or 0 if queue is empty
*/
QT *dequeue()
{
QT *result = _head;
/* check if queue has only one last element */
if (_head == _tail) {
_head = 0;
_tail = 0;
} else
_head = _head->Fifo::Element::_next;
/* mark fifo queue element as free */
if (result) {
result->Fifo::Element::_next = 0;
result->Fifo::Element::_is_enqueued = false;
}
return result;
}
};
}
#endif /* _INCLUDE__UTIL__FIFO_H_ */