MSMQ transport is built into the core NServiceBus NuGet package.
Because of the way MSMQ API has been designed i.e. polling receive that throws an exception when timeout is reached the receive algorithm is more complex than for other polling-driven transports (such as SQLServer).
The main loop starts by subscribing to
PeekCompleted event and calling the
BeginPeek method. When a message arrives the event is raised by the MSMQ client API. The handler for this event starts a new receiving task and waits till this new task has completed its
Receive call. After that is calls
BeginPeek again to wait for more messages.
MSMQ Transport supports the following Transport Transaction Modes:
- Transaction scope (Distributed transaction)
- Transport transaction - Sends atomic with Receive
- Transport transaction - Receive Only
- Unreliable (Transactions Disabled)
See also Controlling Transaction Scope Options.
In this mode the ambient transaction is started before receiving the message. The transaction encompasses all stages of processing including user data access and saga data access.
In this mode, when a message is received, it is immediately removed from the input queue. If processing fails the message is lost because the operation cannot be rolled back. Any other operation that is performed, when processing the message, is executed without a transaction and cannot be rolled back. This can lead to undesired side effects when message processing fails part way through.