TYPE - The concrete type of the data that can be read using the
the DataReader that created this ReadCondition.public interface ReadCondition<TYPE> extends Closeable, Condition
DataReader.
ReadCondition objects allow an application to specify the data samples it
is interested in by specifying the desired sample states, view states,
and instance states. (See Subscriber.DataState.)
This allows the middleware to enable the condition only when suitable
information is available. They are to be used in conjunction with a
WaitSet as normal conditions. More than one ReadCondition may be
attached to the same DataReader.
Similar to the StatusCondition, a ReadCondition also has a
triggerValue that determines whether the attached WaitSet is
BLOCKED or UNBLOCKED. However, unlike the StatusCondition, the
triggerValue of the ReadCondition is tied to the presence of at least a
sample managed by the Service with SampleState, ViewState,
and InstanceState matching those of the ReadCondition.
The fact that the triggerValue of a ReadCondition is dependent on the
presence of samples on the associated DataReader implies that a single
DataReader.take() operation can potentially change the
triggerValue of several ReadCondition or QueryCondition
conditions. For example, if all samples are taken, any ReadCondition and
QueryCondition conditions associated with the DataReader that had their
triggerValue == true before will see the triggerValue change to false.
Note that this does not guarantee that WaitSet objects that were
separately attached to those conditions will not be woken up. Once we have
triggerValue == true on a condition it may wake up the attached WaitSet,
the condition transitioning to triggerValue == false does not necessarily
'unwakeup' the WaitSet as 'unwakening' may not be possible in general. The
consequence is that an application blocked on a WaitSet may return from
the wait with a list of conditions. some of which are no longer "active."
This is unavoidable if multiple threads are concurrently waiting on
separate WaitSet objects and taking data associated with the same
DataReader entity.
To elaborate further, consider the following example: A ReadCondition that
has a sample state collection of {NOT_READ} will have triggerValue of true
whenever a new sample arrives and will transition to false as soon as all
the newly-arrived samples are either read (so their status changes to
SampleState.READ) or taken (so they are no longer managed by the
Service). However if the same ReadCondition had a sample_statesample state
collection of {READ, NOT_READ}, then the triggerValue would only become
false once all the newly-arrived samples are taken (it is not sufficient
to read them as that would only change the SampleState to READ, which
overlaps the collection on the ReadCondition.| Modifier and Type | Method and Description |
|---|---|
void |
close()
Reclaim any resources associated with this condition.
|
Set<InstanceState> |
getInstanceStates()
This operation returns the set of instance states that are taken into
account to determine the triggerValue of the ReadCondition.
|
DataReader<TYPE> |
getParent() |
Set<SampleState> |
getSampleStates()
This operation returns the set of sample states that are taken into
account to determine the triggerValue of the ReadCondition.
|
Set<ViewState> |
getViewStates()
This operation returns the set of view states that are taken into
account to determine the triggerValue of the ReadCondition.
|
getTriggerValuegetEnvironmentSet<SampleState> getSampleStates()
Set<ViewState> getViewStates()
Set<InstanceState> getInstanceStates()
DataReader<TYPE> getParent()
void close()
close in interface AutoCloseableclose in interface CloseableCopyright © 2014. All rights reserved.