EDU.oswego.cs.dl.util.concurrent
public class CondVar extends Object
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; } }
Field Summary | |
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protected Sync | mutex_ The mutex * |
Constructor Summary | |
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CondVar(Sync mutex)
Create a new CondVar that relies on the given mutual
exclusion lock. |
Method Summary | |
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void | await()
Wait for notification. |
void | broadcast() Notify all waiting threads * |
void | signal()
Notify a waiting thread.
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boolean | timedwait(long msecs)
Wait for at most msecs for notification.
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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 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.
Throws: InterruptedException if the thread was interrupted before or during the wait. However, if the thread is interrupted after the wait but during mutex re-acquisition, the interruption is ignored, while still ensuring that the currentThread's interruption state stays true, so can be probed by callers.
Parameters: 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.
Returns: 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.
Throws: InterruptedException if the thread was interrupted before or during the wait.