EDU.oswego.cs.dl.util.concurrent
Class CondVar
java.lang.Object
EDU.oswego.cs.dl.util.concurrent.CondVar
public class CondVar
extends java.lang.Object
This class is designed for fans of POSIX pthreads programming.
If you restrict yourself to Mutexes and CondVars, you can
use most of your favorite constructions. Don't randomly mix them
with synchronized methods or blocks though.
Method names and behavior are as close as is reasonable to
those in POSIX.
Sample Usage. Here is a full version of a bounded buffer
that implements the BoundedChannel interface, written in
a style reminscent of that in POSIX programming books.
class CVBuffer implements BoundedChannel {
private final Mutex mutex;
private final CondVar notFull;
private final CondVar notEmpty;
private int count = 0;
private int takePtr = 0;
private int putPtr = 0;
private final Object[] array;
public CVBuffer(int capacity) {
array = new Object[capacity];
mutex = new Mutex();
notFull = new CondVar(mutex);
notEmpty = new CondVar(mutex);
}
public int capacity() { return array.length; }
public void put(Object x) throws InterruptedException {
mutex.acquire();
try {
while (count == array.length) {
notFull.await();
}
array[putPtr] = x;
putPtr = (putPtr + 1) % array.length;
++count;
notEmpty.signal();
}
finally {
mutex.release();
}
}
public Object take() throws InterruptedException {
Object x = null;
mutex.acquire();
try {
while (count == 0) {
notEmpty.await();
}
x = array[takePtr];
array[takePtr] = null;
takePtr = (takePtr + 1) % array.length;
--count;
notFull.signal();
}
finally {
mutex.release();
}
return x;
}
public boolean offer(Object x, long msecs) throws InterruptedException {
mutex.acquire();
try {
if (count == array.length) {
notFull.timedwait(msecs);
if (count == array.length)
return false;
}
array[putPtr] = x;
putPtr = (putPtr + 1) % array.length;
++count;
notEmpty.signal();
return true;
}
finally {
mutex.release();
}
}
public Object poll(long msecs) throws InterruptedException {
Object x = null;
mutex.acquire();
try {
if (count == 0) {
notEmpty.timedwait(msecs);
if (count == 0)
return null;
}
x = array[takePtr];
array[takePtr] = null;
takePtr = (takePtr + 1) % array.length;
--count;
notFull.signal();
}
finally {
mutex.release();
}
return x;
}
}
CondVar(Sync mutex) - Create a new CondVar that relies on the given mutual
exclusion lock.
|
void | await() - Wait for notification.
|
void | broadcast() - Notify all waiting threads *
|
void | signal() - Notify a waiting thread.
|
boolean | timedwait(long msecs) - Wait for at most msecs for notification.
|
mutex_
protected final Sync mutex_
The mutex *
CondVar
public CondVar(Sync mutex)
Create a new CondVar that relies on the given mutual
exclusion lock.
mutex
- A non-reentrant mutual exclusion lock.
Standard usage is to supply an instance of Mutex
,
but, for example, a Semaphore initialized to 1 also works.
On the other hand, many other Sync implementations would not
work here, so some care is required to supply a sensible
synchronization object.
In normal use, the mutex should be one that is used for all
synchronization of the object using the CondVar. Generally,
to prevent nested monitor lockouts, this
object should not use any native Java synchronized blocks.
await
public void await()
throws InterruptedException
Wait for notification. This operation at least momentarily
releases the mutex. The mutex is always held upon return,
even if interrupted.
broadcast
public void broadcast()
Notify all waiting threads *
signal
public void signal()
Notify a waiting thread.
If one exists, a non-interrupted thread will return
normally (i.e., not via InterruptedException) from await or timedwait.
timedwait
public boolean timedwait(long msecs)
throws InterruptedException
Wait for at most msecs for notification.
This operation at least momentarily
releases the mutex. The mutex is always held upon return,
even if interrupted.
msecs
- The time to wait. A value less than or equal to zero
causes a momentarily release
and re-acquire of the mutex, and always returns false.
- false if at least msecs have elapsed
upon resumption; else true. A
false return does NOT necessarily imply that the thread was
not notified. For example, it might have been notified
after the time elapsed but just before resuming.