| java.lang.Object
 EDU.oswego.cs.dl.util.concurrent.CondVar
| CondVar | | public class CondVar (Code) | | 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;
}
}
See Also: Mutex
See Also: [ Introduction to this package. ] |
| Constructor Summary | |
| public | CondVar(Sync mutex)
Create a new CondVar that relies on the given mutual
exclusion lock. |
| Method Summary | |
| public void | await()
Wait for notification. | | public synchronized void | broadcast()
| | public synchronized void | signal()
Notify a waiting thread. | | public boolean | timedwait(long msecs)
Wait for at most msecs for notification. |
| mutex_ | | final protected Sync mutex_(Code) | | The mutex *
|
| CondVar | | public CondVar(Sync mutex)(Code) | | Create a new CondVar that relies on the given mutual
exclusion lock.
Parameters:
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 notwork here, so some care is required to supply a sensible synchronization object.In normal use, the mutex should be one that is used for allsynchronization of the object using the CondVar. Generally, to prevent nested monitor lockouts, thisobject should not use any native Java synchronized blocks. |
| await | | public void await() throws InterruptedException(Code) | | Wait for notification. This operation at least momentarily
releases the mutex. The mutex is always held upon return,
even if interrupted.
exception:
InterruptedException - if the thread was interruptedbefore or during the wait. However, if the thread is interruptedafter the wait but during mutex re-acquisition, the interruption is ignored, while still ensuringthat the currentThread's interruption state stays true, so canbe probed by callers. |
| broadcast | | public synchronized void broadcast()(Code) | | Notify all waiting threads *
|
| signal | | public synchronized void signal()(Code) | | 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(Code) | | 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.
Parameters:
msecs - The time to wait. A value less than or equal to zero causes a momentarily releaseand re-acquire of the mutex, and always returns false. false if at least msecs have elapsedupon resumption; else true. A false return does NOT necessarily imply that the thread wasnot notified. For example, it might have been notified after the time elapsed but just before resuming.
exception:
InterruptedException - if the thread was interruptedbefore or during the wait. |
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