NIFI-5867 - add thread() EL function to get thread name

moved thread name evaluation in evaluate method

Signed-off-by: Matthew Burgess <mattyb149@apache.org>

This closes #3198

nifi-commons/nifi-expression-language/src/main/antlr3/org/apache/nifi/attribute/expression/language/antlr/AttributeExpressionLexer.g

@@ -107,6 +107,7 @@ IP	: 'ip';
 UUID : 'UUID';
 HOSTNAME : 'hostname';	// requires boolean arg: prefer FQDN
 NOW	: 'now';
+THREAD : 'thread';
 
 
 // 0 arg functions

nifi-commons/nifi-expression-language/src/main/antlr3/org/apache/nifi/attribute/expression/language/antlr/AttributeExpressionParser.g

@@ -128,7 +128,7 @@ functionCall : functionRef ->
 	^(FUNCTION_CALL functionRef);
 
 booleanLiteral : TRUE | FALSE;
-zeroArgStandaloneFunction : (IP | UUID | NOW | NEXT_INT | HOSTNAME | RANDOM) LPAREN! RPAREN!;
+zeroArgStandaloneFunction : (IP | UUID | NOW | NEXT_INT | HOSTNAME | THREAD | RANDOM) LPAREN! RPAREN!;
 oneArgStandaloneFunction : ((TO_LITERAL | MATH | GET_STATE_VALUE)^ LPAREN! anyArg RPAREN!) |
                            (HOSTNAME^ LPAREN! booleanLiteral RPAREN!);
 standaloneFunction : zeroArgStandaloneFunction | oneArgStandaloneFunction;

nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/compile/ExpressionCompiler.java

@@ -91,6 +91,7 @@ import org.apache.nifi.attribute.expression.language.evaluation.functions.Substr
 import org.apache.nifi.attribute.expression.language.evaluation.functions.SubstringBeforeEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.functions.SubstringBeforeLastEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.functions.SubstringEvaluator;
+import org.apache.nifi.attribute.expression.language.evaluation.functions.ThreadEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.functions.ToLowerEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.functions.ToRadixEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.functions.ToStringEvaluator;
@@ -199,6 +200,7 @@ import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpre
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.SUBSTRING_AFTER_LAST;
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.SUBSTRING_BEFORE;
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.SUBSTRING_BEFORE_LAST;
+import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.THREAD;
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.TO_DATE;
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.TO_DECIMAL;
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.TO_LITERAL;
@@ -1009,6 +1011,8 @@ public class ExpressionCompiler {
                     throw new AttributeExpressionLanguageException(e);
                 }
             }
+            case THREAD:
+                return addToken(new ThreadEvaluator(), "thread");
             case HOSTNAME: {
                 if (tree.getChildCount() == 0) {
                     try {

nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/evaluation/functions/ThreadEvaluator.java

@@ -0,0 +1,39 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.nifi.attribute.expression.language.evaluation.functions;
+
+import java.util.Map;
+
+import org.apache.nifi.attribute.expression.language.evaluation.Evaluator;
+import org.apache.nifi.attribute.expression.language.evaluation.QueryResult;
+import org.apache.nifi.attribute.expression.language.evaluation.StringEvaluator;
+import org.apache.nifi.attribute.expression.language.evaluation.StringQueryResult;
+
+public class ThreadEvaluator extends StringEvaluator {
+
+    @Override
+    public QueryResult<String> evaluate(final Map<String, String> attributes) {
+        // See org.apache.nifi.engine.FlowEngine
+        return new StringQueryResult(Thread.currentThread().getName());
+    }
+
+    @Override
+    public Evaluator<?> getSubjectEvaluator() {
+        return null;
+    }
+
+}

nifi-commons/nifi-expression-language/src/test/java/org/apache/nifi/attribute/expression/language/TestQuery.java

@@ -1810,6 +1810,11 @@ public class TestQuery {
         verifyEquals("${literal(true):ifElse(false, 'b')}", attributes, "false");
     }
 
+    @Test
+    public void testThread() {
+        final Map<String, String> attributes = new HashMap<>();
+        verifyEquals("${thread()}", attributes, "main");
+    }
 
     private void verifyEquals(final String expression, final Map<String, String> attributes, final Object expectedResult) {
         verifyEquals(expression,attributes, null, expectedResult);

nifi-docs/src/main/asciidoc/expression-language-guide.adoc

@@ -2062,6 +2062,24 @@ names begin with the letter `a`.
 
 *Examples*: UpdateAttribute processor has stored the key "count" with value "20" in state. '${getStateValue("count")}` returns `20`.
 
+
+
+[.function]
+=== thread
+
+*Description*: [.description]#Returns the name of the thread used by the processor when evaluating the Expression. This can be useful
+ when using a processor with multiple concurrent tasks and where some data uniqueness is required.#
+
+*Subject Type*: [.subjectless]#No Subject#
+
+*Arguments*: No arguments
+
+*Return Type*: [.returnType]#String#
+
+*Examples*: `${thread()}` could return something like `Timer-Driven Process Thread-4`.
+
+
+
 [[multi]]
 == Evaluating Multiple Attributes