IBM BPM, V8.0.1, All platforms > Programming IBM BPM > Service Component Architecture programming > SCA programming model fundamentals > Invocation styles
Asynchronous invocation
IBM BPM delivers a powerful programming model for developing asynchronous applications. With asynchronous invocation in SCA, there are three types of asynchronous interaction styles available: one way, deferred response, and request with callback. With all three types of asynchronous invocation, the client receives control back immediately from the SCA runtime upon an invokeAsync() call.
In addition to its published APIs and tools to develop asynchronous programs using Java™, IBM BPM also comes with a number of built-in asynchronous messaging bindings and built-in asynchronous components.
Asynchronous invocation is said to be one way if the client does not want to capture a response at all. This can only be selected on a one way operation.
There are two different ways that the client can capture the response at a later time. One is for the client to call invokeAsync() and then continue processing until some later time when the client makes a request to capture the response. This scenario is termed deferred response, and it can only be selected on a request-response operation. Alternatively the client also has the option of doing an asynchronous request with callback. To do this, the client must first implement the ServiceCallback interface. Then, after calling invokeAsyncWithCallback(), the SCA runtime provides a callback to the ServiceCallback handler to provide the response to the client. Asynchronous with callback can only be used on a request-response operation, and should only be used if the mediation flow component is invoked as asynchronous with callback.
Figure 1. Asynchronous invocation models
SCA interfaces are always defined in the synchronous form. For each synchronous interface, one or more asynchronous interfaces can be generated. When a callback mechanism is chosen by the client, the client component needs to implement a class: <interface name>.Callback.java. The interface of this class is derived from the interface of the actual component that the client wants to use.