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https://issues.apache.org/jira/browse/FLINK-10470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16639833#comment-16639833
]
ASF GitHub Bot commented on FLINK-10470:
----------------------------------------
dawidwys closed pull request #6781: [FLINK-10470] Add method to check if
pattern can produce empty matches
URL: https://github.com/apache/flink/pull/6781
This is a PR merged from a forked repository.
As GitHub hides the original diff on merge, it is displayed below for
the sake of provenance:
As this is a foreign pull request (from a fork), the diff is supplied
below (as it won't show otherwise due to GitHub magic):
diff --git
a/flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
b/flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
index 8f49f68fe41..ed2ff2e7e59 100644
---
a/flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
+++
b/flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
@@ -40,8 +40,13 @@
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
+import java.util.HashSet;
import java.util.List;
import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+import static org.apache.flink.util.Preconditions.checkNotNull;
/**
* Compiler class containing methods to compile a {@link Pattern} into a
{@link NFA} or a
@@ -74,6 +79,44 @@
}
}
+ /**
+ * Verifies if the provided pattern can possibly generate empty match.
Example of patterns that can possibly
+ * generate empty matches are: A*, A?, A* B? etc.
+ *
+ * @param pattern pattern to check
+ * @return true if empty match could potentially match the pattern,
false otherwise
+ */
+ public static boolean canProduceEmptyMatches(final Pattern<?, ?>
pattern) {
+ NFAFactoryCompiler<?> compiler = new
NFAFactoryCompiler<>(checkNotNull(pattern));
+ compiler.compileFactory();
+ State<?> startState =
compiler.getStates().stream().filter(State::isStart).findFirst().orElseThrow(
+ () -> new IllegalStateException("Compiler produced no
start state. It is a bug. File a jira."));
+
+ Set<State<?>> visitedStates = new HashSet<>();
+ final Stack<State<?>> statesToCheck = new Stack<>();
+ statesToCheck.push(startState);
+ while (!statesToCheck.isEmpty()) {
+ final State<?> currentState = statesToCheck.pop();
+ if (visitedStates.contains(currentState)) {
+ continue;
+ } else {
+ visitedStates.add(currentState);
+ }
+
+ for (StateTransition<?> transition :
currentState.getStateTransitions()) {
+ if (transition.getAction() ==
StateTransitionAction.PROCEED) {
+ if
(transition.getTargetState().isFinal()) {
+ return true;
+ } else {
+
statesToCheck.push(transition.getTargetState());
+ }
+ }
+ }
+ }
+
+ return false;
+ }
+
/**
* Converts a {@link Pattern} into graph of {@link State}. It enables
sharing of
* compilation state across methods.
diff --git
a/flink-libraries/flink-cep/src/test/java/org/apache/flink/cep/nfa/compiler/NFACompilerTest.java
b/flink-libraries/flink-cep/src/test/java/org/apache/flink/cep/nfa/compiler/NFACompilerTest.java
index f39b17483cd..821da031c6d 100644
---
a/flink-libraries/flink-cep/src/test/java/org/apache/flink/cep/nfa/compiler/NFACompilerTest.java
+++
b/flink-libraries/flink-cep/src/test/java/org/apache/flink/cep/nfa/compiler/NFACompilerTest.java
@@ -44,7 +44,9 @@
import java.util.Set;
import static org.apache.flink.cep.utils.NFAUtils.compile;
+import static org.hamcrest.Matchers.is;
import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertTrue;
/**
@@ -226,4 +228,14 @@ public boolean filter(Event value) throws Exception {
return transitions;
}
+ @Test
+ public void testCheckingEmptyMatches() {
+
assertThat(NFACompiler.canProduceEmptyMatches(Pattern.begin("a").optional()),
is(true));
+
assertThat(NFACompiler.canProduceEmptyMatches(Pattern.begin("a").oneOrMore().optional()),
is(true));
+
assertThat(NFACompiler.canProduceEmptyMatches(Pattern.begin("a").oneOrMore().optional().next("b").optional()),
is(true));
+
+
assertThat(NFACompiler.canProduceEmptyMatches(Pattern.begin("a")), is(false));
+
assertThat(NFACompiler.canProduceEmptyMatches(Pattern.begin("a").oneOrMore()),
is(false));
+
assertThat(NFACompiler.canProduceEmptyMatches(Pattern.begin("a").oneOrMore().next("b").optional()),
is(false));
+ }
}
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> Add method to check if pattern can produce empty matches
> --------------------------------------------------------
>
> Key: FLINK-10470
> URL: https://issues.apache.org/jira/browse/FLINK-10470
> Project: Flink
> Issue Type: Sub-task
> Components: CEP
> Reporter: Dawid Wysakowicz
> Assignee: Dawid Wysakowicz
> Priority: Major
> Labels: pull-request-available
>
> There is couple of inconsistencies how CEP library handles greedy and
> reluctant operators at the beginning at end of pattern. This results in
> subtle problems how empty matches should be generated for patterns like e.g.
> A? or A*?, where one is greedy and the other one is reluctant. In order to
> provide first version of MATCH_RECOGNIZE function we should have a
> possibility to disable patterns which can produce empty matches.
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