Fix lock not working for multiple transactions started at the same time

Author: pbbadenhorst

example/src/tests/rawQueries.spec.ts

@@ -391,6 +391,46 @@ export function registerBaseTests() {
       }, 1000);
     });
 
+    it('Async transaction, upsert and select', done => {
+      // ARRANGE: Setup for multiple transactions
+      const iterations = 10;
+      const actual = new Set();
+
+      // ARRANGE: Generate expected data
+      const id = chance.integer();
+      const name = chance.name();
+      const age = chance.integer();
+
+      // ACT: Start multiple async transactions to upsert and select the same record
+      for (let iteration = 1; iteration <= iterations; iteration++) {
+        db.transactionAsync(async (tx) => {
+          // ACT: Upsert statement to create record / increment the value
+          await tx.executeAsync(`
+            INSERT OR REPLACE INTO [User] ([id], [name], [age], [networth])
+            SELECT ?, ?, ?,
+              IFNULL((
+                SELECT [networth] + 1000
+                FROM [User]
+                WHERE [id] = ?
+              ), 1000)
+          `, [id, name, age, id]);
+
+          // ACT: Select statement to get incremented value and store it for checking later
+          const results = await tx.executeAsync('SELECT [networth] FROM [User] WHERE [id] = ?', [id]);
+
+          actual.add(results.rows._array[0].networth);
+        })
+      }
+
+      // ACT: Wait for all transactions to complete
+      setTimeout(() => {
+        // ASSERT: That the expected values where returned
+        expect(actual.size).to.equal(iterations, 'Each transaction should read a different value');
+
+        done();
+      }, 1000);
+    });
+
     it('Batch execute', () => {
       const id1 = chance.integer();
       const name1 = chance.name();

src/index.ts

@@ -354,21 +354,22 @@ QuickSQLite.transactionAsync = (
 };
 
 const startNextTransaction = (dbName: string) => {
+  if (!locks[dbName]) {
+    throw Error(`Lock not found for db: ${dbName}`);
+  }
+
   if (locks[dbName].inProgress) {
     // Transaction is already in process bail out
     return;
   }
 
-  setImmediate(() => {
-    if (!locks[dbName]) {
-      throw Error(`Lock not found for db: ${dbName}`);
-    }
-
     if (locks[dbName].queue.length) {
       locks[dbName].inProgress = true;
-      locks[dbName].queue.shift().start();
-    }
+    const tx = locks[dbName].queue.shift();
+    setImmediate(() => {
+      tx.start();
   });
+  }
 };
 
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