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.
By default, queues are created with
Anonymous Logon permissions to allow messages to be sent and received without additional configuration. If required, the appropriate permissions can be set on a queue after its creation.
- Administer Security for Message Queuing in Windows Server 2003.
- Message Queuing Security Overview in Windows Server 2008.
Often when debugging MSMQ using native tools it is helpful to have some custom text in the MSMQ Label. For example the message type or the message id. As of Version 6 the text used to apply to Message.Label can be controlled at configuration time using the
ApplyLabelToMessages extension method. This method takes a delegate which will be passed the header collection and should return a string to use for the label. It will be called for all standard messages as well as Audits, Errors and all control messages. The only exception to this rule is received messages with corrupted headers. In some cases it may be useful to use the
Headers.ControlMessageHeader key to determine if a message is a control message. These messages will be forwarded to the error queue with no label applied. The returned string can be
String.Empty for no label and must be at most 240 characters.
var transport = endpointConfiguration.UseTransport<MsmqTransport>(); // Set the msmq message label to the current Message Id transport.ApplyLabelToMessages(headers => headers[NServiceBus.Headers.MessageId]);
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. If all the logical data stores (transport, user data, saga data) use the same physical store there is no escalation to Distributed Transaction Coordinator (DTC).
In Versions 6.1 and above, the MSMQ transport uses native transactions to support the
SendsAtomicWithReceive levels. With
SendsAtomicWithReceive the native transaction for receiving messages is shared with sending operations. That means the message receive operation, and any send or publish operations, are committed atomically. When using
ReceiveOnly, the transaction is not shared with sending operations and dispatched messages may not be rolled back in case the receiving transaction needs to abort.
SendsAtomicWithReceiveand both levels behaving as
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.