Fix error when converting multiple units parallel with the same UnitConverter instance

common/changes/@itwin/ecschema-metadata/fix-parallel-unit-conversion_2025-01-28-16-04.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@itwin/ecschema-metadata",
+      "comment": "Fix for error occuring when converting multiple units with the same UnitConverter instance",
+      "type": "none"
+    }
+  ],
+  "packageName": "@itwin/ecschema-metadata"
+}

core/ecschema-metadata/src/UnitConversion/UnitTree.ts

@@ -52,6 +52,7 @@ export class GraphUtils {
 /** @internal */
 export class UnitGraph {
   private _graph = new Graph<Unit | Constant>();
+  private _unitsInProgress = new Map<string, Promise<void>>();
 
   constructor(private _context: SchemaContext) {
     this._graph.setGraph("Unit tree processor");
@@ -120,13 +121,24 @@ export class UnitGraph {
    * @param unit Current unit to be added to graph
    */
   public async addUnit(unit: Unit | Constant): Promise<void> {
+    if(this._unitsInProgress.has(unit.key.fullName))
+      return this._unitsInProgress.get(unit.key.fullName);
+
     if (this._graph.hasNode(unit.key.fullName))
       return;
 
     this._graph.setNode(unit.key.fullName, unit);
     if (this.isIdentity(unit))
       return;
 
+    const promise = this.addUnitToGraph(unit);
+    this._unitsInProgress.set(unit.key.fullName, promise);
+
+    await promise
+      .finally(() => this._unitsInProgress.delete(unit.key.fullName));
+  }
+
+  private async addUnitToGraph(unit: Unit | Constant) {
     const umap = parseDefinition(unit.definition);
 
     const promiseArray: Promise<[Unit | Constant, DefinitionFragment]>[] = [];

core/ecschema-metadata/src/test/UnitConversion/Convert.test.ts

@@ -30,18 +30,31 @@ describe("Unit Conversion tests", () => {
     deserializeXmlSync(schemaXml, context);
   });
 
+  async function convertAndVerifyTestData(test: TestData, converter: UnitConverter) {
+    const fromFullName = `Units:${test.from}`;
+    const toFullName = `Units:${test.to}`;
+    const map = await converter.calculateConversion(fromFullName, toFullName);
+    const actual = map.evaluate(test.input);
+    expect(
+      almostEqual(test.expect, actual, tolerance),
+      `${test.input} ${test.from} in ${test.to} should be ${test.expect}
+       and not ${actual} error = ${Math.abs(test.expect - actual)} > ${tolerance}`,
+    ).to.be.true;
+  }
+
   testData.forEach((test: TestData) => {
     it(`should convert ${test.from} to ${test.to}`, async () => {
       const converter = new UnitConverter(context);
-      const fromFullName = `Units:${test.from}`;
-      const toFullName = `Units:${test.to}`;
-      const map = await converter.calculateConversion(fromFullName, toFullName);
-      const actual = map.evaluate(test.input);
-      expect(
-        almostEqual(test.expect, actual, tolerance),
-        `${test.input} ${test.from} in ${test.to} should be ${test.expect}
-         and not ${actual} error = ${Math.abs(test.expect - actual)} > ${tolerance}`,
-      ).to.be.true;
+      await convertAndVerifyTestData(test, converter);
     });
   });
+
+  it(`should convert units parallel`, async () => {
+    const converter = new UnitConverter(context);
+    const conversionPromises = testData.map(async (test: TestData) => {
+      await convertAndVerifyTestData(test, converter);
+    });
+
+    await Promise.all(conversionPromises);
+  });
 });