Public Member Functions | |
this (int count) | |
void | wait () |
bool | wait (long timeout, TimeUnit unit) |
void | countDown () |
long | count () |
char[] | toString () |
Private Attributes | |
Sync | sync |
Classes | |
class | Sync |
A CountDownLatch
is initialized with a given count. The wait methods block until the current count reaches zero due to invocations of the countDown method, after which all waiting threads are released and any subsequent invocations of wait return immediately. This is a one-shot phenomenon -- the count cannot be reset. If you need a version that resets the count, consider using a CyclicBarrier.
A CountDownLatch
is a versatile synchronization tool and can be used for a number of purposes. A CountDownLatch
initialized with a count of one serves as a simple on/off latch, or gate: all threads invoking wait wait at the gate until it is opened by a thread invoking countDown. A CountDownLatch
initialized to N can be used to make one thread wait until N threads have completed some action, or some action has been completed N times.
A useful property of a CountDownLatch
is that it doesn't require that threads calling countDown
wait for the count to reach zero before proceeding, it simply prevents any thread from proceeding past an wait until all threads could pass.
Sample usage: Here is a pair of classes in which a group of worker threads use two countdown latches:
class Driver { void main() { CountDownLatch startSignal; CountDownLatch doneSignal; this() { startSignal = new CountDownLatch(1); doneSignal = new CountDownLatch(N); } for (int i = 0; i < N; ++i) { // create and start threads Worker work = new Worker(startSignal, doneSignal); new Thread(&work.run).start(); doSomethingElse(); // don't let run yet startSignal.countDown(); // let all threads proceed doSomethingElse(); doneSignal.wait(); // wait for all to finish } } class Worker { private CountDownLatch startSignal; private CountDownLatch doneSignal; this(CountDownLatch startSignal, CountDownLatch doneSignal) { this.startSignal = startSignal; this.doneSignal = doneSignal; } int run() { startSignal.wait(); doWork(); doneSignal.countDown(); return 0; } void doWork() { ... } } *
Definition at line 99 of file Countdown.d.
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Constructs a
Definition at line 140 of file Countdown.d. References count(). |
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Causes the current thread to wait until the latch has counted down to zero. If the current count is zero then this method returns immediately. If the current count is greater than zero then the current thread becomes disabled for thread scheduling purposes and lies dormant until the count reaches zero due to invocations of the countDown method. Definition at line 156 of file Countdown.d. References AbstractLock::acquireShared(), and sync. |
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Causes the current thread to wait until the latch has counted down to zero.
If the current count is zero then this method returns immediately with the value If the current count is greater than zero then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of three things happen:
If the count reaches zero then the method returns with the value
If the specified waiting time elapses then the value
Definition at line 186 of file Countdown.d. References sync, toNanos(), and AbstractLock::tryAcquireSharedNanos(). |
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Decrements the count of the latch, releasing all waiting threads if the count reaches zero. If the current count is greater than zero then it is decremented. If the new count is zero then all waiting threads are re-enabled for thread scheduling purposes. If the current count equals zero then nothing happens. Definition at line 200 of file Countdown.d. References AbstractLock::releaseShared(), and sync. |
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Returns the current count. This method is typically used for debugging and testing purposes.
Definition at line 209 of file Countdown.d. References CountDownLatch::Sync::getCount(), and sync. Referenced by this(). |
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Returns a string identifying this latch, as well as its state. The state, in brackets, includes the String "Count =" followed by the current count.
Definition at line 219 of file Countdown.d. References CountDownLatch::Sync::getCount(), and sync. |
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Definition at line 131 of file Countdown.d. Referenced by count(), countDown(), toString(), and wait(). |