Chapter 1

This encapsulation is important, as it ensures we cannot inadvertently change state at an
inappropriate time.
An initial state change occurs every time the task represented by the state machine is
invoked. This may be through an external request (a 'send packet' request, for example) or
just by opening the state machine. This can then cause a whole sequence of successive
asynchronous requests, each with a corresponding state change. While these asynchronous
operations are taking place, the task is 'active', meaning that no further external requests
can be serviced until we're finished with this one. Finally, when no more asynchronous
requests are required, the task returns to 'inactive' and the state machine is able to accept
further client requests.
For every state change, there are two phases, as shown in Figure 20.2. First, we issue a
request to enter the new state – which in turn will issue an asynchronous request – and
second, we complete the entry to the state, when the asynchronous request completes. At
this point, there may be another state change – and further asynchronous request(s) – or the
task may just complete. The latter case signifies the completion of the external request, and
the machine moves back to its inactive mode waiting for another request.
Figure 20.2
The actual code to change state is as follows:
void CGdpStateMachine::ChangeState(CGdpStateMachine::TState*
aNextState)
{
// Enter aNextState, and make it our current state.
__ASSERT_ALWAYS(!IsActive(),
GdpUtil::Panic(GdpUtil::EStateMachineStateError));
TInt err;
while(aNextState)
{
// State change required.
iState = aNextState;