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// package NexusII.util ;
// The minimun functionality to be associated with a queue
interface Queue
{
public void nq(Object item);
public Object dq();
public boolean is_full();
public boolean is_empty();
public static final int DEF_SIZE = 1;
};
// Specific Conditions associated with MT_Bounded_Queue
// Is true if there is space in the queue
class Not_Full_Condition extends Timed_Wait
{
public Not_Full_Condition(MT_Bounded_Queue q)
{
super(q);
}
public synchronized boolean condition()
{
MT_Bounded_Queue mq_ = (MT_Bounded_Queue) object_;
return !mq_.is_full ();
}
}
// Is true if there's something in the queue
class Not_Empty_Condition extends Timed_Wait
{
public Not_Empty_Condition(MT_Bounded_Queue q)
{
super(q);
}
public synchronized boolean condition()
{
// Delegate to the appropriate conditional
// check on the MessageQueue.
MT_Bounded_Queue mq_ = (MT_Bounded_Queue) object_;
return !mq_.is_empty ();
}
private MT_Bounded_Queue mq_ ;
}
// Encapsulates a bounded - synchronized queue
public class MT_Bounded_Queue implements Queue
{
private Object[] queue_ ;
private int front_ ;
private int back_ ;
private int max_size_ ;
private int size_ ;
private Not_Empty_Condition not_empty_condition_ ;
private Not_Full_Condition not_full_condition_ ;
private int nq_count_ ;
private int dq_count_ ;
// The counters counts the number of nq's and dq's operations made on this
// instance of the queue
public int dq_count()
{
return dq_count_ ;
}
public int nq_count()
{
return nq_count_ ;
}
public MT_Bounded_Queue()
{
// call the other constructor with DEF_SIZE
this(DEF_SIZE);
}
public MT_Bounded_Queue(int max_size)
{
this.front_ = 0 ;
this.back_ = 0 ;
this.max_size_ = max_size ;
this.size_ = 0 ;
// these are included for STATISTICS
this.nq_count_ = 0 ;
this.dq_count_ = 0 ;
this.queue_ = new Object[this.max_size_];
not_full_condition_ = new Not_Full_Condition(this);
not_empty_condition_ = new Not_Empty_Condition(this);
}
// Blocking nq
public synchronized void nq(Object item)
{
// Wait till the queue has space
while(is_full())
{
try {
wait();
} catch (InterruptedException e) {}
}
// enqueue here
queue_[back_] = item ;
back_ = (back_ + 1) % max_size_ ;
size_++ ;
// One more enqueue operation has occured
nq_count_ ++ ;
// wakeup the sleeping guys
notifyAll();
}
// Timed nq
// returns -1 if timed_out
public synchronized int nq(Object item,long msec_timeout)
{
// Wait till the queue has space
try {
not_full_condition_.timed_wait(msec_timeout);
} catch (InterruptedException e) {}
catch (TimeoutException t)
{
return -1 ;
}
// enqueue here
queue_[back_] = item ;
back_ = (back_ + 1) % max_size_ ;
size_++ ;
// One more enqueue operation has occured
nq_count_ ++ ;
// wakeup the sleeping consumers
not_empty_condition_.broadcast ();
return 0 ;
}
// Blockin dq
public synchronized Object dq()
{
// wait till the queue has something in it
while(is_empty())
{
try {
wait();
} catch (InterruptedException e) {}
}
// dequeue here
Object return_object = queue_[front_] ;
front_ = (front_ + 1) % max_size_ ;
size_ -- ;
// One more enqueue operation has occured
dq_count_ ++ ;
//wake up the sleeping producers
notifyAll();
return return_object ;
}
// Timed dq
public synchronized Object dq(long msec_timeout)
{
// wait till the queue has something in it
try {
not_empty_condition_.timed_wait(msec_timeout);
} catch (InterruptedException e) {}
catch (TimeoutException t)
{
return null;
}
// dequeue here
Object return_object = queue_[front_] ;
front_ = (front_ + 1) % max_size_ ;
size_ -- ;
// One more enqueue operation has occured
dq_count_ ++ ;
//wake up the sleeping guys
not_full_condition_.broadcast();
return return_object ;
}
public boolean is_empty()
{
if (size_ == 0)
return true ;
else
return false ;
}
public boolean is_full()
{
if (size_ == max_size_)
return true ;
else
return false ;
}
}
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