sqlite: fix crash session extension callbacks with workers

src/node_sqlite.cc

@@ -1647,26 +1647,28 @@ void Backup(const FunctionCallbackInfo<Value>& args) {
   job->ScheduleBackup();
 }
 
+struct ConflictCallbackContext {
+  std::function<bool(std::string)> filterCallback;
+  std::function<int(int)> conflictCallback;
+};
+
 // the reason for using static functions here is that SQLite needs a
 // function pointer
-static std::function<int(int)> conflictCallback;
 
 static int xConflict(void* pCtx, int eConflict, sqlite3_changeset_iter* pIter) {
-  if (!conflictCallback) return SQLITE_CHANGESET_ABORT;
-  return conflictCallback(eConflict);
+  auto ctx = static_cast<ConflictCallbackContext*>(pCtx);
+  if (!ctx->conflictCallback) return SQLITE_CHANGESET_ABORT;
+  return ctx->conflictCallback(eConflict);
 }
 
-static std::function<bool(std::string)> filterCallback;
-
 static int xFilter(void* pCtx, const char* zTab) {
-  if (!filterCallback) return 1;
-
-  return filterCallback(zTab) ? 1 : 0;
+  auto ctx = static_cast<ConflictCallbackContext*>(pCtx);
+  if (!ctx->filterCallback) return 1;
+  return ctx->filterCallback(zTab) ? 1 : 0;
 }
 
 void DatabaseSync::ApplyChangeset(const FunctionCallbackInfo<Value>& args) {
-  conflictCallback = nullptr;
-  filterCallback = nullptr;
+  ConflictCallbackContext context;
 
   DatabaseSync* db;
   ASSIGN_OR_RETURN_UNWRAP(&db, args.This());
@@ -1702,7 +1704,7 @@ void DatabaseSync::ApplyChangeset(const FunctionCallbackInfo<Value>& args) {
         return;
       }
       Local<Function> conflictFunc = conflictValue.As<Function>();
-      conflictCallback = [env, conflictFunc](int conflictType) -> int {
+      context.conflictCallback = [env, conflictFunc](int conflictType) -> int {
         Local<Value> argv[] = {Integer::New(env->isolate(), conflictType)};
         TryCatch try_catch(env->isolate());
         Local<Value> result =
@@ -1740,7 +1742,7 @@ void DatabaseSync::ApplyChangeset(const FunctionCallbackInfo<Value>& args) {
 
       Local<Function> filterFunc = filterValue.As<Function>();
 
-      filterCallback = [env, filterFunc](std::string item) -> bool {
+      context.filterCallback = [env, filterFunc](std::string item) -> bool {
         // TODO(@jasnell): The use of ToLocalChecked here means that if
         // the filter function throws an error the process will crash.
         // The filterCallback should be updated to avoid the check and
@@ -1764,7 +1766,7 @@ void DatabaseSync::ApplyChangeset(const FunctionCallbackInfo<Value>& args) {
       const_cast<void*>(static_cast<const void*>(buf.data())),
       xFilter,
       xConflict,
-      nullptr);
+      static_cast<void*>(&context));
   if (r == SQLITE_OK) {
     args.GetReturnValue().Set(true);
     return;

test/parallel/test-sqlite-session.js

@@ -7,6 +7,9 @@ const {
   constants,
 } = require('node:sqlite');
 const { test, suite } = require('node:test');
+const { nextDb } = require('../sqlite/next-db.js');
+const { Worker } = require('worker_threads');
+const { once } = require('events');
 
 /**
  * Convenience wrapper around assert.deepStrictEqual that sets a null
@@ -555,3 +558,74 @@ test('session supports ERM', (t) => {
     message: /session is not open/,
   });
 });
+
+test('concurrent applyChangeset with workers', async (t) => {
+  // Before adding this test, the callbacks were stored in static variables
+  // this could result in a crash
+  // this test is a regression test for that scenario
+
+  function modeToString(mode) {
+    if (mode === constants.SQLITE_CHANGESET_ABORT) return 'SQLITE_CHANGESET_ABORT';
+    if (mode === constants.SQLITE_CHANGESET_OMIT) return 'SQLITE_CHANGESET_OMIT';
+  }
+
+  const dbPath = nextDb();
+  const db1 = new DatabaseSync(dbPath);
+  const db2 = new DatabaseSync(':memory:');
+  const createTable = `
+    CREATE TABLE data(
+      key INTEGER PRIMARY KEY,
+      value TEXT
+    ) STRICT`;
+  db1.exec(createTable);
+  db2.exec(createTable);
+  db1.prepare('INSERT INTO data (key, value) VALUES (?, ?)').run(1, 'hello');
+  db1.close();
+  const session = db2.createSession();
+  db2.prepare('INSERT INTO data (key, value) VALUES (?, ?)').run(1, 'world');
+  const changeset = session.changeset(); // Changeset with conflict (for db1)
+
+  const iterations = 10;
+  for (let i = 0; i < iterations; i++) {
+    const workers = [];
+    const expectedResults = new Map([
+      [constants.SQLITE_CHANGESET_ABORT, false],
+      [constants.SQLITE_CHANGESET_OMIT, true]]
+    );
+
+    // Launch two workers (abort and omit modes)
+    for (const mode of [constants.SQLITE_CHANGESET_ABORT, constants.SQLITE_CHANGESET_OMIT]) {
+      const worker = new Worker(`${__dirname}/../sqlite/worker.js`, {
+        workerData: {
+          dbPath,
+          changeset,
+          mode
+        },
+      });
+      workers.push(worker);
+    }
+
+    const results = await Promise.all(workers.map(async (worker) => {
+      const [message] = await once(worker, 'message');
+      return message;
+    }));
+
+    // Verify each result
+    for (const res of results) {
+      if (res.errorMessage) {
+        if (res.errcode === 5) {  // SQLITE_BUSY
+          break; // ignore
+        }
+        t.assert.fail(`Worker error: ${res.error.message}`);
+      }
+      const expected = expectedResults.get(res.mode);
+      t.assert.strictEqual(
+        res.result,
+        expected,
+        `Iteration ${i}: Worker (${modeToString(res.mode)}) expected ${expected} but got ${res.result}`
+      );
+    }
+
+    workers.forEach((worker) => worker.terminate()); // Cleanup
+  }
+});

test/parallel/test-sqlite.js

@@ -1,18 +1,10 @@
 'use strict';
 const { spawnPromisified, skipIfSQLiteMissing } = require('../common');
 skipIfSQLiteMissing();
-const tmpdir = require('../common/tmpdir');
-const { join } = require('node:path');
 const { DatabaseSync, constants } = require('node:sqlite');
 const { suite, test } = require('node:test');
 const { pathToFileURL } = require('node:url');
-let cnt = 0;
-
-tmpdir.refresh();
-
-function nextDb() {
-  return join(tmpdir.path, `database-${cnt++}.db`);
-}
+const { nextDb } = require('../sqlite/next-db.js');
 
 suite('accessing the node:sqlite module', () => {
   test('cannot be accessed without the node: scheme', (t) => {

test/sqlite/next-db.js

@@ -0,0 +1,14 @@
+'use strict';
+require('../common');
+const tmpdir = require('../common/tmpdir');
+const { join } = require('node:path');
+
+let cnt = 0;
+
+tmpdir.refresh();
+
+function nextDb() {
+  return join(tmpdir.path, `database-${cnt++}.db`);
+}
+
+module.exports = { nextDb };

test/sqlite/worker.js

@@ -0,0 +1,24 @@
+// This worker is used for one of the tests in test-sqlite-session.js
+
+'use strict';
+require('../common');
+const { parentPort, workerData } = require('worker_threads');
+const { DatabaseSync, constants } = require('node:sqlite');
+const { changeset, mode, dbPath } = workerData;
+
+const db = new DatabaseSync(dbPath);
+
+const options = {};
+if (mode !== constants.SQLITE_CHANGESET_ABORT && mode !== constants.SQLITE_CHANGESET_OMIT) {
+  throw new Error('Unexpected value for mode');
+}
+options.onConflict = () => mode;
+
+try {
+  const result = db.applyChangeset(changeset, options);
+  parentPort.postMessage({ mode, result, error: null });
+} catch (error) {
+  parentPort.postMessage({ mode, result: null, errorMessage: error.message, errcode: error.errcode });
+} finally {
+  db.close();  // Just to make sure it is closed ASAP
+}