Chapter 1

};
Figure 17.9
Member functions here are as follows:
Function Description
~CActive() Virtual destructor. Calls Deque() to de-queue the object from the
active scheduler.
Cancel() Cancels a request. If a request is active, calls
DoCancel(), waits synchronously for completion on iStatus and sets the request
as no longer active.
SetPriority() Changes the priority after construction.
Priority() Returns the active object's priority.
IsActive() Indicates whether a request is outstanding.
Deque() Removes this object from the active scheduler.
IsAdded() Indicates whether the object has been added to the active scheduler.
CActive() C++ constructor: you must specify the active object's priority as a
constructor parameter.
SetActive() Call this function after you have issued a request function to indicate
that a request is outstanding.
DoCancel() Implement this in a derived class to cancel a request issued to an
asynchronous service provider. This function can only be called if a
request is active. You must provide a way to cancel requests.
RunL() Implement this in a derived class to handle the completion of a
request that was issued.
RunError() This should be overridden if the RunL()implementation calls a leaving
function. The TInt parameter is the leave code from RunL().
I've not yet met a case in which Deque() or SetPriority() are necessary or couldn't be
handled by a different design approach. Bizarrely, although Deque() is a member of
CActive, which enables you to remove an active object from the scheduler, you can only
add an active object to the scheduler using a member function of
CActiveScheduler(which is a friend class).