feat(#3840): Fix Concurrency Issue Related to TrStepped

eo-parser/src/main/java/org/eolang/parser/TrStepped.java

@@ -31,13 +31,15 @@
 import com.yegor256.xsline.TrEnvelope;
 import com.yegor256.xsline.TrLambda;
 import com.yegor256.xsline.Train;
+import java.util.concurrent.CountDownLatch;
 import org.cactoos.Scalar;
 import org.cactoos.io.ResourceOf;
 import org.cactoos.scalar.Sticky;
+import org.cactoos.scalar.Synced;
 import org.cactoos.text.TextOf;
 
 /**
- * Trains that adds sheet names that were processed.
+ * Train that adds sheet names that were processed.
  *
  * @since 0.1
  */
@@ -47,26 +49,39 @@ final class TrStepped extends TrEnvelope {
      * Apply changes to each XML after processing.
      */
     private static final Scalar<XSL> STEPPED = new Sticky<>(
-        () -> new XSLDocument(
-            new TextOf(
-                new ResourceOf("org/eolang/parser/_stepped.xsl")
-            ).asString()
+        new Once<XSL>(
+            () -> new XSLDocument(
+                new TextOf(
+                    new ResourceOf("org/eolang/parser/_stepped.xsl")
+                ).asString()
+            )
         )
     );
 
     /**
      * Ctor.
+     *
      * @param train Original train
      */
     TrStepped(final Train<Shift> train) {
+        this(train, TrStepped.STEPPED);
+    }
+
+    /**
+     * Ctor.
+     *
+     * @param train Original train
+     * @param stepped XSL to apply
+     */
+    TrStepped(final Train<Shift> train, final Scalar<XSL> stepped) {
         super(
             new TrLambda(
                 train,
                 shift -> new StAfter(
                     shift,
                     new StLambda(
                         shift::uid,
-                        (pos, xml) -> TrStepped.STEPPED.value()
+                        (pos, xml) -> new Synced<>(stepped).value()
                             .with("step", pos)
                             .with("sheet", shift.uid())
                             .transform(xml)
@@ -75,4 +90,54 @@ final class TrStepped extends TrEnvelope {
             )
         );
     }
+
+    /**
+     * Scalar that loads the value only once.
+     *
+     * @param <T> Type of the value
+     * @since 0.51
+     */
+    static final class Once<T> implements Scalar<T> {
+
+        /**
+         * Origin scalar.
+         */
+        private final Scalar<T> origin;
+
+        /**
+         * Latch to count down.
+         */
+        private final CountDownLatch latch;
+
+        /**
+         * Ctor.
+         *
+         * @param origin Origin scalar
+         */
+        Once(final Scalar<T> origin) {
+            this(origin, new CountDownLatch(1));
+        }
+
+        /**
+         * Ctor.
+         *
+         * @param origin Origin scalar
+         * @param latch Latch to count down
+         */
+        private Once(final Scalar<T> origin, final CountDownLatch latch) {
+            this.origin = origin;
+            this.latch = latch;
+        }
+
+        @Override
+        public T value() throws Exception {
+            if (this.latch.getCount() < 1) {
+                throw new IllegalStateException(
+                    String.format("Resource '%s' should be loaded only once", this.origin)
+                );
+            }
+            this.latch.countDown();
+            return this.origin.value();
+        }
+    }
 }

eo-parser/src/test/java/org/eolang/parser/TrSteppedTest.java

@@ -0,0 +1,92 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016-2025 Objectionary.com
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package org.eolang.parser;
+
+import com.jcabi.matchers.XhtmlMatchers;
+import com.jcabi.xml.XML;
+import com.jcabi.xml.XMLDocument;
+import com.jcabi.xml.XSL;
+import com.jcabi.xml.XSLDocument;
+import com.yegor256.Together;
+import com.yegor256.xsline.Shift;
+import com.yegor256.xsline.StClasspath;
+import com.yegor256.xsline.TrDefault;
+import com.yegor256.xsline.Xsline;
+import org.cactoos.io.ResourceOf;
+import org.cactoos.scalar.Sticky;
+import org.cactoos.text.TextOf;
+import org.hamcrest.MatcherAssert;
+import org.junit.jupiter.api.RepeatedTest;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test cases for {@link TrStepped}.
+ *
+ * @since 0.51
+ */
+final class TrSteppedTest {
+
+    @Test
+    void addsSheetName() {
+        MatcherAssert.assertThat(
+            "We expect the sheet name to be added",
+            new Xsline(
+                new TrStepped(
+                    new TrDefault<Shift>().with(
+                        new StClasspath("/org/eolang/parser/print/wrap-data.xsl")
+                    )
+                )
+            ).pass(new XMLDocument("<program><concurrency>no</concurrency></program>")).toString(),
+            XhtmlMatchers.hasXPath("/program/sheets/sheet[text()='wrap-data']")
+        );
+    }
+
+    @RepeatedTest(10)
+    void addsSheetNameConcurrently() {
+        final XML doc = new XMLDocument("<program><concurrency>yes</concurrency></program>");
+        final Sticky<XSL> loading = new Sticky<>(
+            new TrStepped.Once<XSL>(
+                () -> new XSLDocument(
+                    new TextOf(
+                        () -> new ResourceOf("org/eolang/parser/_stepped.xsl").stream()
+                    ).asString()
+                )
+            )
+        );
+        MatcherAssert.assertThat(
+            "We expect the sheet name to be added successfully in concurrent environment",
+            new Together<>(
+                i -> new Xsline(
+                    new TrStepped(
+                        new TrDefault<Shift>().with(
+                            new StClasspath("/org/eolang/parser/print/wrap-data.xsl")
+                        ),
+                        loading
+                    )
+                ).pass(doc).toString()
+            ).iterator().next(),
+            XhtmlMatchers.hasXPath("/program/sheets/sheet[text()='wrap-data']")
+        );
+    }
+}