public interface ICountDownLatch extends DistributedObject
ICountDownLatch is a cluster-wide synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes.
There are a few differences compared to the
trySetCount(int)after a countdown has finished but not during an active count. This allows the same latch instance to be reused.
ICountDownLatchimpls. Behaviour of
ICountDownLatchunder failure scenarios, including network partitions, depend on the impl. The first impl is the one accessed via
HazelcastInstance.getCountDownLatch(String). This impl works on top of Hazelcast's async replication algorithm and does not guarantee linearizability during failures. During a split, each partitioned cluster will either create a brand new and uninitialised (zero'd)
ICountDownLatchinstance, or it will continue to use the primary or backup replica. For example, it is possible for both the primary and backup replicas to be resident in one cluster partition, and for another one to be created as new in the other side of the network partition. In any of these cases, the counter value in the respective
ICountDownLatchinstance may diverge.
In this impl, when the split heals, Hazelcast performs a default largest
cluster wins resolution, or a random winner is chosen where clusters sizes
are equal. This can lead to situations where the
can fall into an unpredictable state, and a countdown to zero may never be
If required, when using
ICountDownLatch as an orchestration
mechanism, you should assess the state of the orchestration outcome and
the associated countdown actors after a split-brain heal has taken place,
and take steps to re-orchestrate if needed.
ICountDownLatch impl is a new one introduced with the
CPSubsystem in version 3.12. It is accessed via
CPSubsystem.getCountDownLatch(String). It has a major difference to
the old implementation, that is, it works on top of the Raft consensus
algorithm. It offers linearizability during crash failures and network
partitions. It is CP with respect to the CAP principle. If a network
partition occurs, it remains available on at most one side of the partition.
All of the API methods in the new CP
ICountDownLatch impl offer
the exactly-once execution semantics. For instance, even if
countDown() call is internally retried because of crashed
Hazelcast member, the counter value is decremented only once.
|Modifier and Type||Method and Description|
Causes the current thread to wait until the latch has counted down to zero, or an exception is thrown, or the specified waiting time elapses.
Decrements the count of the latch, releasing all waiting threads if the count reaches zero.
Returns the current count.
Sets the count to the given value if the current count is zero.
boolean await(long timeout, TimeUnit unit) throws InterruptedException
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 five things happen:
If the current thread:
InterruptedExceptionis thrown and the current thread's interrupted status is cleared.
If the specified waiting time elapses then the value
is returned. If the time is less than or equal to zero, the method
will not wait at all.
timeout- the maximum time to wait
unit- the time unit of the
trueif the count reached zero,
falseif the waiting time elapsed before the count reached zero
InterruptedException- if the current thread is interrupted
IllegalStateException- if the Hazelcast instance is shutdown while waiting
NullPointerException- if unit is null
If the current count is greater than zero, then it is decremented. If the new count is zero:
boolean trySetCount(int count)
If count is not zero, then this method does nothing and returns
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