Github user ddebrunner commented on a diff in the pull request:
https://github.com/apache/incubator-quarks/pull/93#discussion_r60314136
--- Diff:
analytics/sensors/src/main/java/quarks/analytics/sensors/Valve.java ---
@@ -0,0 +1,91 @@
+package quarks.analytics.sensors;
+
+import java.util.Objects;
+
+import quarks.function.Predicate;
+
+/**
+ * A generic "valve" {@link Predicate}.
+ * <p>
+ * A valve predicate accepts tuples when its state is {@link State#OPEN},
+ * otherwise it rejects tuples.
+ * </p><p>
+ * A valve is typically used to dynamically control whether or not
+ * some downstream tuple processing is enabled. A decision to change the
+ * state of the valve may be a result of local analytics or an external
+ * command.
+ * <br>
+ * E.g., a Valve might be used to control whether or not logging
+ * of tuples is enabled.
+ * <pre>{@code
+ * TStream<JsonObject> stream = ...;
+ *
+ * Valve<JsonObject> valve = new Valve<>(Valve.State.CLOSED);
+ * stream.filter(valve).sink(someTupleLoggingConsumer);
+ *
+ * // from some analytic or device command handler...
+ * valve.setState(Valve.State.OPEN);
+ * }</pre>
+ * </p>
+ *
+ * @param <T> tuple type
+ */
+public class Valve<T> implements Predicate<T> {
+ private static final long serialVersionUID = 1L;
+ private transient State state = State.OPEN;
+
+ /**
+ * The valve state.
+ */
+ public enum State {
--- End diff --
Is there value to an enum as opposed to just a boolean? It seems to be
extra (minimal) footprint for little benefit.
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