Stateful Service Operations

To better understand how to manage state from the client side, let us take a quick look at how Services on TIBCO GridServer® manage it. Let’s consider our JavaCalculatorExample Service.

The state maintained by the Service is a field called memory. There are two methods that are responsible for updating the state:

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addToMemory

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setMemory

Although both methods update the state, TIBCO GridServer® has to handle them differently to ensure that the state is properly maintained. addToMemory refers to the previous value of memory, whereas setMemory does not. TIBCO GridServer® denotes the first type of method as an appendStateMethod, and the second type as setStateMethod.

When a Service instance is created on an Engine, the Engine replays all state-changing methods from the last setStateMethod, or from the beginning if there have been no setStateMethods. Depending on the duration of the request, it might be worthwhile to follow appendStateMethods with setStateMethods periodically, to save memory on the Manager.

These special state-changing methods have to be identified when the Service is registered in TIBCO GridServer®. Within the Service configuration of the JavaCalculatorExample, under the section ContainerBinding, these method names must be included in the fields titled appendStateMethods and setStateMethods.

Once the methods have been registered on the Service, a client can only access them through the updateState functions. These functions behave in a similar way to execute functions. They take three input arguments:

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methodName — the name of the method to invoke;

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data — the input data;

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append — a Boolean signifying whether it is an appendStateMethod and updates the state accordingly.

These functions do not return output arguments.

In the same manner as execute and submit, one of two updateState methods are more suitable depending on the number of input arguments that the Service function takes. These functions are: updateState and updateStateWithArray.

The following Visual Basic code updates the memory of the JavaCalculatorExample:

service.updateState "setToMemory", "25", False
service.updateState "addToMemory", "75", True

The resultant value of memory is 100.