Core/DBLayer: Implement async transaction completion callbacks

src/server/database/Database/Transaction.cpp

@@ -65,7 +65,7 @@ void TransactionBase::Cleanup()
 
 bool TransactionTask::Execute()
 {
-    int errorCode = m_conn->ExecuteTransaction(m_trans);
+    int errorCode = TryExecute();
     if (!errorCode)
         return true;
 
@@ -75,12 +75,64 @@ bool TransactionTask::Execute()
         std::lock_guard<std::mutex> lock(_deadlockLock);
         uint8 loopBreaker = 5;  // Handle MySQL Errno 1213 without extending deadlock to the core itself
         for (uint8 i = 0; i < loopBreaker; ++i)
-            if (!m_conn->ExecuteTransaction(m_trans))
+            if (!TryExecute())
                 return true;
     }
 
     // Clean up now.
-    m_trans->Cleanup();
+    CleanupOnFailure();
+
+    return false;
+}
+
+int TransactionTask::TryExecute()
+{
+    return m_conn->ExecuteTransaction(m_trans);
+}
+
+void TransactionTask::CleanupOnFailure()
+{
+    m_trans->Cleanup();
+}
+
+bool TransactionWithResultTask::Execute()
+{
+    int errorCode = TryExecute();
+    if (!errorCode)
+    {
+        m_result.set_value(true);
+        return true;
+    }
+
+    if (errorCode == ER_LOCK_DEADLOCK)
+    {
+        // Make sure only 1 async thread retries a transaction so they don't keep dead-locking each other
+        std::lock_guard<std::mutex> lock(_deadlockLock);
+        uint8 loopBreaker = 5;  // Handle MySQL Errno 1213 without extending deadlock to the core itself
+        for (uint8 i = 0; i < loopBreaker; ++i)
+        {
+            if (!TryExecute())
+            {
+                m_result.set_value(true);
+                return true;
+            }
+        }
+    }
+
+    // Clean up now.
+    CleanupOnFailure();
+    m_result.set_value(false);
+
+    return false;
+}
+
+bool TransactionCallback::InvokeIfReady()
+{
+    if (m_future.valid() && m_future.wait_for(std::chrono::seconds(0)) == std::future_status::ready)
+    {
+        m_callback(m_future.get());
+        return true;
+    }
 
     return false;
 }