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/*
D-Bus Java Implementation
Copyright (c) 2005-2006 Matthew Johnson
This program is free software; you can redistribute it and/or modify it
under the terms of either the GNU Lesser General Public License Version 2 or the
Academic Free Licence Version 2.1.
Full licence texts are included in the COPYING file with this program.
*/
package org.freedesktop.dbus;
import cx.ath.matthew.debug.Debug;
/**
* Provides a Message queue which doesn't allocate objects
* on insertion/removal. */
class EfficientQueue
{
private Message[] mv;
private int start;
private int end;
private int init_size;
public EfficientQueue(int initial_size)
{
init_size = initial_size;
shrink();
}
private void grow()
{
if (Debug.debug) Debug.print(Debug.DEBUG, "Growing");
// create new vectors twice as long
Message[] oldmv = mv;
mv = new Message[oldmv.length*2];
// copy start->length to the start of the new vector
System.arraycopy(oldmv,start,mv,0,oldmv.length-start);
// copy 0->end to the next part of the new vector
if (end != (oldmv.length-1)) {
System.arraycopy(oldmv,0,mv,oldmv.length-start,end+1);
}
// reposition pointers
start = 0;
end = oldmv.length;
}
// create a new vector with just the valid keys in and return it
public Message[] getKeys()
{
if (start == end) return new Message[0];
Message[] lv;
if (start < end) {
int size = end-start;
lv = new Message[size];
System.arraycopy(mv, start, lv, 0, size);
} else {
int size = mv.length-start+end;
lv = new Message[size];
System.arraycopy(mv, start, lv, 0, mv.length-start);
System.arraycopy(mv, 0, lv, mv.length-start, end);
}
return lv;
}
private void shrink()
{
if (Debug.debug) Debug.print(Debug.DEBUG, "Shrinking");
if (null != mv && mv.length == init_size) return;
// reset to original size
mv = new Message[init_size];
start = 0;
end = 0;
}
public void add(Message m)
{
if (Debug.debug) Debug.print(Debug.DEBUG, "Enqueueing Message "+m);
// put this at the end
mv[end] = m;
// move the end
if (end == (mv.length-1)) end = 0; else end++;
// if we are out of space, grow.
if (end == start) grow();
}
public Message remove()
{
if (start == end) return null;
// find the item
int pos = start;
// get the value
Message m = mv[pos];
// set it as unused
mv[pos] = null;
if (start == (mv.length-1)) start = 0; else start++;
if (Debug.debug) Debug.print(Debug.DEBUG, "Dequeueing "+m);
return m;
}
public boolean isEmpty()
{
// check if find succeeds
return start == end;
}
public int size()
{
if (end >= start)
return end-start;
else
return mv.length-start+end;
}
}
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