CActive Class Reference

class CActive : public CBase

The core class of the active object abstraction.

It encapsulates both the issuing of a request to an asynchronous service provider and the handling of completed requests. An application can have one or more active objects whose processing is controlled by an active scheduler.

Inherits from

Constructor & Destructor Documentation



Constructs the active object with the specified priority.

Derived classes must define and implement a constructor through which the priority can be specified. A typical implementation calls this active object constructor through a constructor initialization list.


TInt aPriorityAn integer specifying the priority of this active object. CActive::TPriority defines a standard set of priorities.



Frees resources prior to destruction.

Specifically, it removes this active object from the active scheduler's list of active objects.

Typically, a derived class calls Cancel() in its destructor.

E32USER-CBase 40 if the active object has an outstanding request when the destructor is called,

Member Functions Documentation


IMPORT_C voidCancel()

Cancels the wait for completion of an outstanding request.

If there is no request outstanding, then the function does nothing.

If there is an outstanding request, the function:

1. calls the active object's DoCancel() function, provided by the derived class to implement cancellation of the request.

2. waits for the cancelled request to complete; this must complete as fast as possible.

3. marks the active object's request as complete (i.e. the request is no longer outstanding).

CActive::DoCancel CActive::IsActive CActive::~CActive User::WaitForRequest


IMPORT_C voidDeque()

Removes the active object from the active scheduler's list of active objects.

Before being removed from the active scheduler's list, the function cancels any outstanding request.



voidDoCancel()[protected, pure virtual]

Implements cancellation of an outstanding request.

This function is called as part of the active object's Cancel().

It must call the appropriate cancel function offered by the active object's asynchronous service provider. The asynchronous service provider's cancel is expected to act immediately.

DoCancel() must not wait for event completion; this is handled by Cancel().


Extension_(TUint, TAny *&, TAny *)

IMPORT_C TIntExtension_(TUintaExtensionId,
TAny *&a0,
TAny *a1
)[protected, virtual]

Extension function


TUint aExtensionId
TAny *& a0
TAny * a1


TBool IsActive()const [inline]

Determines whether the active object has a request outstanding.

A request is outstanding when:

1. it has been issued

2. it has not been cancelled

3. it servicing has not yet begun.


TBool IsAdded()const [inline]

Determines whether the active object has been added to the active scheduler's list of active objects.

If the active object has not been added to a scheduler, it cannot handle the completion of any request. No request should be issued until the active object has been added to a scheduler because completion of that request generates what appears to be a stray signal.

Use the active object function Deque() to remove the active object from the scheduler.



TInt Priority()const [inline]

Gets the priority of the active object.


IMPORT_C TIntRunError(TIntaError)[protected, virtual]

Handles a leave occurring in the request completion event handler RunL().

The active scheduler calls this function if this active object's RunL() function leaves. This gives this active object the opportunity to perform any necessary cleanup.

A derived class implementation should handle the leave and return KErrNone. Returning any other value results in the active scheduler function CActiveScheduler::Error() being called.

The default implementation simply returns the leave code.

Note that if the active scheduler is to handle the error, a suitably derived CActiveScheduler::Error() function must be supplied.



TInt aErrorThe leave code


voidRunL()[protected, pure virtual]

Handles an active object's request completion event.

A derived class must provide an implementation to handle the completed request. If appropriate, it may issue another request.

The function is called by the active scheduler when a request completion event occurs, i.e. after the active scheduler's WaitForAnyRequest() function completes.

Before calling this active object's RunL() function, the active scheduler has:

1. decided that this is the highest priority active object with a completed request

2. marked this active object's request as complete (i.e. the request is no longer outstanding)

RunL() runs under a trap harness in the active scheduler. If it leaves, then the active scheduler calls RunError() to handle the leave.

Note that once the active scheduler's Start() function has been called, all user code is run under one of the program's active object's RunL() or RunError() functions.

CActiveScheduler::Start CActiveScheduler::Error CActiveScheduler::WaitForAnyRequest TRAPD


IMPORT_C voidSetActive()[protected]

Indicates that the active object has issued a request and that it is now outstanding.

Derived classes must call this function after issuing a request.

A request is automatically marked as complete (i.e. it is no longer outstanding) by:

1. the active scheduler, immediately before it calls the active object's RunL() function.


2. the active object within the implementation of the Cancel() function.

E32USER-CBase 46 panics may occur if an active object is set active but no request is made on its TRequestStatus, or vice-versa. This panic happens no earlier than the next time that the active scheduler assesses which objects are ready to run, and may happen much later. This panic is termed a 'stray event' because it indicates that some entity has sent an event to the active scheduler thread, but this thread is not in a state ready to handle it.

CActive::IsActive CActive::RunL CActive::Cancel
E32USER-CBase 42 if this active object is already active
E32USER-CBase 49 if this active object has not been added to the active scheduler.


IMPORT_C voidSetPriority(TIntaPriority)

Sets the priority of the active object.

E32USER-CBase 50 if this function is called while a request is outstanding.


TInt aPriorityAn integer specifying the new priority of this active object. CActive::TPriority defines a standard set of priorities.

Member Enumerations Documentation

Enum TPriority

Defines standard priorities for active objects.


EPriorityIdle = -100

A low priority, useful for active objects representing background processing.

EPriorityLow = -20

A priority higher than EPriorityIdle but lower than EPriorityStandard.

EPriorityStandard = 0

Most active objects will have this priority.

EPriorityUserInput = 10

A priority higher than EPriorityStandard; useful for active objects handling user input.

EPriorityHigh = 20

A priority higher than EPriorityUserInput.

Member Data Documentation

TPriQueLink iLink

TPriQueLink iLink[private]

TAny * iSpare

TAny *iSpare[private]

TRequestStatus iStatus

TRequestStatus iStatus

The request status associated with an asynchronous request.

This is passed as a parameter to all asynchronous service providers.

The active scheduler uses this to check whether the active object's request has completed.

The function can use the completion code to judge the success or otherwise of the request.