In one form, a method for managing message flow includes processing messages concurrently by processing nodes in a computer software application. The processing nodes include at least one set of lock acquisition, system resource access and lock release nodes interconnected in a flow path. In such a set, the nodes are interconnected in a flow path and process a respective one of the messages in a sequence defined by the flow path. The processing includes granting access to a system resource exclusively for the set's respective message responsive to the lock acquisition node processing its respective message. The system resource is accessed for the message responsive to the set's system resource node processing the message. The accessing of the resource for the message includes changing a certain system state. The exclusive accessing of the system resource is released responsive to the set's lock release node processing the message.