tillrohrmann commented on a change in pull request #15251:
URL: https://github.com/apache/flink/pull/15251#discussion_r597597099
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/scheduler/adaptive/allocator/SlotAllocator.java
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@@ -45,27 +42,26 @@
* <p>If a {@link VertexParallelism} is returned then it covers all
vertices contained in the
* given job information.
*
- * <p>A returned {@link VertexParallelism} should be directly consumed
afterwards (by either
- * discarding it or calling {@link #reserveResources(VertexParallelism)},
as there is no
- * guarantee that the assignment remains valid over time (because slots
can be lost).
- *
* <p>Implementations of this method must be side-effect free. There is no
guarantee that the
- * result of this method is ever passed to {@link
#reserveResources(VertexParallelism)}.
+ * result of this method is ever passed to {@link
#tryReserveResources(VertexParallelism)}.
*
* @param jobInformation information about the job graph
* @param slots slots to consider for determining the parallelism
* @return potential parallelism for all vertices and
implementation-specific information for
* how the vertices could be assigned to slots, if all vertices could
be run with the given
* slots
*/
- Optional<T> determineParallelism(
+ Optional<? extends VertexParallelism> determineParallelism(
JobInformation jobInformation, Collection<? extends SlotInfo>
slots);
/**
- * Reserves slots according to the given assignment.
+ * Reserves slots according to the given assignment if possible. If the
underlying set of
+ * resources has changed and the reservation with respect to
vertexParallelism is no longer
+ * possible, then this method returns {@link Optional#empty()}.
*
* @param vertexParallelism information on how slots should be assigned to
the slots
- * @return mapping of vertices to slots
+ * @return Set of reserved slots if the reservation was successful;
otherwise {@link
+ * Optional#empty()}
*/
- Map<ExecutionVertexID, LogicalSlot> reserveResources(T vertexParallelism);
+ Optional<? extends ReservedSlots> tryReserveResources(VertexParallelism
vertexParallelism);
Review comment:
The idea is to have a way to tell the caller that the `SlotAllocator`
could not reserve the required slots for the given `VertexParallelism`. The
alternative would be to return an empty `ReservedSlots` instance but this would
be a bit less expressive but also possible.
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