Class CountDown
- java.lang.Object
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- EDU.oswego.cs.dl.util.concurrent.CountDown
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- All Implemented Interfaces:
Sync
public class CountDown extends java.lang.Object implements Sync
A CountDown can serve as a simple one-shot barrier. A Countdown is initialized with a given count value. Each release decrements the count. All acquires block until the count reaches zero. Upon reaching zero all current acquires are unblocked and all subsequent acquires pass without blocking. This is a one-shot phenomenon -- the count cannot be reset. If you need a version that resets the count, consider using a Barrier.Sample usage. Here are a set of classes in which a group of worker threads use a countdown to notify a driver when all threads are complete.
class Worker implements Runnable { private final CountDown done; Worker(CountDown d) { done = d; } public void run() { doWork(); done.release(); } } class Driver { // ... void main() { CountDown done = new CountDown(N); for (int i = 0; i < N; ++i) new Thread(new Worker(done)).start(); doSomethingElse(); done.acquire(); // wait for all to finish } }
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Field Summary
Fields Modifier and Type Field Description protected int
count_
protected int
initialCount_
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Fields inherited from interface EDU.oswego.cs.dl.util.concurrent.Sync
ONE_CENTURY, ONE_DAY, ONE_HOUR, ONE_MINUTE, ONE_SECOND, ONE_WEEK, ONE_YEAR
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Constructor Summary
Constructors Constructor Description CountDown(int count)
Create a new CountDown with given count value
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
acquire()
Wait (possibly forever) until successful passage.boolean
attempt(long msecs)
Wait at most msecs to pass; report whether passed.int
currentCount()
Return the current count value.int
initialCount()
Return the initial count valuevoid
release()
Decrement the count.
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Method Detail
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acquire
public void acquire() throws java.lang.InterruptedException
Description copied from interface:Sync
Wait (possibly forever) until successful passage. Fail only upon interuption. Interruptions always result in `clean' failures. On failure, you can be sure that it has not been acquired, and that no corresponding release should be performed. Conversely, a normal return guarantees that the acquire was successful.
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attempt
public boolean attempt(long msecs) throws java.lang.InterruptedException
Description copied from interface:Sync
Wait at most msecs to pass; report whether passed.The method has best-effort semantics: The msecs bound cannot be guaranteed to be a precise upper bound on wait time in Java. Implementations generally can only attempt to return as soon as possible after the specified bound. Also, timers in Java do not stop during garbage collection, so timeouts can occur just because a GC intervened. So, msecs arguments should be used in a coarse-grained manner. Further, implementations cannot always guarantee that this method will return at all without blocking indefinitely when used in unintended ways. For example, deadlocks may be encountered when called in an unintended context.
- Specified by:
attempt
in interfaceSync
- Parameters:
msecs
- the number of milleseconds to wait. An argument less than or equal to zero means not to wait at all. However, this may still require access to a synchronization lock, which can impose unbounded delay if there is a lot of contention among threads.- Returns:
- true if acquired
- Throws:
java.lang.InterruptedException
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release
public void release()
Decrement the count. After the initialCount'th release, all current and future acquires will pass
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initialCount
public int initialCount()
Return the initial count value
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currentCount
public int currentCount()
Return the current count value. This is just a snapshot value, that may change immediately after returning.
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