Fix deadlock between concurrent query worker and main thread

common/changes/@itwin/core-backend/affank-os-deadlock_2026-06-23-14-54.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@itwin/core-backend",
+      "comment": "Add performance test for concurrent query",
+      "type": "none"
+    }
+  ],
+  "packageName": "@itwin/core-backend"
+}

core/backend/src/test/ecdb/ConcurrentQuery.test.ts

@@ -72,7 +72,7 @@ describe("ConcurrentQuery", () => {
     expect(resp.stats.cpuTime).to.be.closeTo(1000970, 500000);
     expect(resp.stats.totalTime).to.be.closeTo(1001, 100);
     expect(resp.stats.memUsed).to.be.closeTo(2, 3);
-    expect(resp.stats.prepareTime).to.be.closeTo(0, 2);
+    expect(resp.stats.prepareTime).to.be.closeTo(0, 4);
     db.close();
   });
 

core/backend/src/test/ecdb/ECDb.test.ts

@@ -164,7 +164,7 @@ describe("ECDb", () => {
         alias: "source",
         fileName: path.join(outDir, "source_file.ecdb"),
         profile: "SQLite"
-      }
+      },
     ]);
     testECDb1.detachDb("source");
     expect(await runDbListPragmaCCQ(testECDb1)).deep.equals([

core/backend/src/test/ecdb/ECSqlStatement.test.ts

@@ -3431,8 +3431,14 @@ describe("ECSqlStatement", () => {
       parentHasChildrenClassId = reader.current.ECInstanceId;
       assert.isTrue(Id64.isValidId64(parentHasChildrenClassId));
 
-      // When the ECSql insert validation is set to true, the invalid relClassId is detected and an error is thrown.
-      assert.isTrue(await (ecdb.createQueryReader("PRAGMA validate_ecsql_writes=true")).step());
+      // Enable ECSql write-value validation so invalid relClassIds are detected and an error is thrown.
+      // This must be set synchronously on the primary connection (the connection on which the write
+      // statements below are prepared and validated). It cannot be set via `createQueryReader`, whose
+      // concurrent-query path executes the pragma on a separate worker connection that does not affect
+      // the primary connection's write validation.
+      ecdb.withWriteStatement("PRAGMA validate_ecsql_writes=true", (stmt: ECSqlWriteStatement) => {
+        assert.equal(stmt.step(), DbResult.BE_SQLITE_ROW);
+      });
 
       reader = ecdb.createQueryReader("SELECT ECInstanceId FROM meta.ECClassDef WHERE Name='ParentHasChildren'");
       assert.isTrue(await reader.step());

full-stack-tests/backend/package.json

@@ -27,6 +27,7 @@
     "perftest:schemaloader": "npm run -s perftest:pre && mocha --timeout=999999999 \"./lib/cjs/perftest/SchemaLoader.test.js\"",
     "perftest:ecSqlRowPerformance": "npm run -s perftest:pre && mocha --timeout=999999999 \"./lib/cjs/perftest/ECSqlRow.test.js\"",
     "perftest:readQueryPerformance": "npm run -s perftest:pre && mocha --timeout=999999999 \"./lib/cjs/perftest/ReadQueryPerf.test.js\"",
+    "perftest:ecSqlReaderConcurrent": "npm run -s perftest:pre && mocha --timeout=999999999 \"./lib/cjs/perftest/ECSqlReaderConcurrentPerf.test.js\"",
     "perftest:metadataPerformance": "npm run -s perftest:pre && mocha --timeout=999999999 --grep PerformanceElementGetMetadata \"./lib/cjs/perftest/ElementCRUD.test.js\"",
     "perftest:schemaContextPerformance": "npm run -s perftest:pre && mocha --timeout=999999999 \"./lib/cjs/perftest/SchemaContextIModelDb.test.js\"",
     "perftest:sqliteChangesetReaderAndChangesetECAdaptorPerformance": "npm run -s perftest:pre && mocha --timeout=999999999 --grep SqliteChangesetReaderAndChangesetECAdaptorAPI \"./lib/cjs/perftest/SQliteChangesetReaderAndChangesetECAdaptor.test.js\"",