Symbian
Symbian OS Library

SYMBIAN OS V9.3

[Index] [Spacer] [Previous] [Next]



Location: e32base.h
Link against: euser.lib

Class CActiveScheduler

class CActiveScheduler : public CBase;

Description

Controls the handling of asynchronous requests as represented by active objects.

An active scheduler is used to schedule the sequence in which active object request completion events are handled by a single event-handling thread.

An active scheduler can be instantiated and used directly if either:

If any of the active scheduler's active objects does not provide a RunError() function, then a CActiveScheduler derived class must be defined and an implementation of the Error() function provided to perform the cleanup required.

There is one active scheduler per thread and the static functions provided by the class always refer to the current active scheduler.

Derivation

Members

Defined in CActiveScheduler:
Add(), CActiveScheduler(), Current(), Error(), Extension_(), Halt(), Install(), Level(), OnStarting(), OnStopping(), Replace(), RunIfReady(), StackDepth(), Start(), Stop(), TLoopOwner, WaitForAnyRequest(), ~CActiveScheduler()

Inherited from CBase:
Delete(), operator new()

See also:


Construction and destruction


CActiveScheduler()

IMPORT_C CActiveScheduler();

Description

Constructs an active scheduler.

After construction, the scheduler should be installed.


~CActiveScheduler()

IMPORT_C ~CActiveScheduler();

Description

Frees resources prior to destruction.

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

An active scheduler should only be destroyed when the top-level call to Start() has returned.

[Top]


Member functions


Install()

static IMPORT_C void Install(CActiveScheduler *aScheduler);

Description

Installs the specified active scheduler as the current active scheduler.

The installed active scheduler now handles events for this thread.

The current active scheduler can be uninstalled by passing a NULL pointer.

Parameters

CActiveScheduler *aScheduler

A pointer to the active scheduler to be installed. If this is NULL, the current active scheduler is uninstalled.

Panic codes

E32USER-CBase

43 if If there is already an installed active scheduler.


Current()

static IMPORT_C CActiveScheduler *Current();

Description

Gets a pointer to the currently installed active scheduler.

Return value

CActiveScheduler *

A pointer to the active scheduler which is currently installed.


Add()

static IMPORT_C void Add(CActive *aActive);

Description

Adds the specified active object to the current active scheduler.

An active object can be removed from an active scheduler either by destroying the active object or by using its Deque() member function.

Parameters

CActive *aActive

Pointer to the active object to be added.

Panic codes

E32USER-CBase

41 if the active object aRequest has already been added to the current active scheduler.

E32USER-CBase

48 if aRequest is NULL.

E32USER-CBase

44 if the thread does not have an installed active scheduler.


Start()

static IMPORT_C void Start();

Description

Starts a new wait loop under the control of the current active scheduler.

At least one active object, with an outstanding request, must be added to the scheduler before the wait loop is started, otherwise no events will occur and the thread will hang, or any events that do occur will be counted as stray signals, raising a panic.

While Start() is executing, user code runs only:

1. in the RunL() function of active objects known to the current active scheduler

2. in the RunError() function of an active object that leaves from its RunL()

3. in the current active scheduler’s Error() function, if an active object’s RunError() returns an error code.

Start() returns only when a corresponding Stop() or Halt() is issued.

Although this can be used to start a nested wait loop, this API is deprecated for that specific functionality, and a CActiveSchedulerWait object should be used instead.

(Note that a nested wait loop is used when the handling of a completed event in an active object requires the processing of further events from the other active objects before it can complete. This is a form of modal processing.)

Panic codes

E32USER-CBase

44 if the thread does not have an active scheduler installed.

See also:


Stop()

static IMPORT_C void Stop();

Description

Stops the wait loop started by the most recent call to Start().

Typically, this is called by the RunL() of one of the scheduler’s active objects. When this RunL() finishes, the scheduler’s wait loop terminates, i.e. it does not wait for the completion of the next request.

It will not stop a wait loop started by a call to CActiveSchedulerWait::Start().

Stop() may also be called from Error().

Note that stopping a nested wait loop is deprecated using this functionality, use a CActiveSchedulerWait object instead.


RunIfReady()

static IMPORT_C TBool RunIfReady(TInt &aError, TInt aMinimumPriority);

Description

Causes the RunL() function of at most one pending active object of priority aMinimumPriority or greater to be run.

Parameters

TInt &aError

Error returned by called active object.

TInt aMinimumPriority

Minimum priority of active object to run.

Return value

TBool

EFalse if no active object's RunL() function was run, i.e. if there were no active objects of priority aMinimumPriority or greater pending.


Replace()

static IMPORT_C CActiveScheduler *Replace(CActiveScheduler *aNewActiveScheduler);

Description

Allows the current active scheduler to be replaced, while retaining its active objects.

Parameters

CActiveScheduler *aNewActiveScheduler

The new active scheduler.

Return value

CActiveScheduler *

Previous active scheduler.


WaitForAnyRequest()

virtual IMPORT_C void WaitForAnyRequest();

Description

Wait for an asynchronous request to complete.

The default implementation just calls User::WaitForAnyRequest().

Derived classes can replace this. Typically, this would be done to implement code for maintaining an outstanding request; this would be followed by a call to User::WaitForAnyRequest().


Error()

virtual IMPORT_C void Error(TInt aError) const;

Description

Handles the result of a leave occurring in an active object’s RunL() function.

An active scheduler always invokes an active object’s RunL() function under a trap harness.

The default implementation must be replaced.

Any cleanup relevant to the possible causes of leaving should be performed. If Stop() or Halt() is called from within this function, the current wait loop terminates. This may be an appropriate response to catastrophic error conditions.

Parameters

TInt aError

The leave code propagated from the active object’s RunL() function

Panic codes

E32USER-CBase

47 if the default implementation is invoked.


Halt()

IMPORT_C void Halt(TInt aExitCode) const;

Description

Unilaterally terminates the current scheduler loop.

This causes the current scheduler loop to stop, whether it was started using CActiveSchedulerWait::Start() or CActiveScheduler::Start(). It can also trigger a leave from Start() if an exit code is provided. If the current level has already been stopped, then this still records the exit code.

Parameters

TInt aExitCode

If non-zero, the reason code reported by Start().


StackDepth()

IMPORT_C TInt StackDepth() const;

Description

Gets the current number of nested wait loops.

Return value

TInt

The number of nested calls to Start().


OnStarting()

private: virtual IMPORT_C void OnStarting();

Description

Dummy EXPORT for Binary Compatibility reasons. This method is never called.


OnStopping()

private: virtual IMPORT_C void OnStopping();

Description

Dummy EXPORT for Binary Compatibility reasons. This method is never called.


Extension_()

protected: virtual IMPORT_C TInt Extension_(TUint aExtensionId, TAny *&a0, TAny *a1);

Description

Extension function

Parameters

TUint aExtensionId

TAny *&a0

TAny *a1

Return value

TInt


Level()

protected: inline TInt Level() const;

Description

Gets the scheduler's level of nestedness.

Return value

TInt

The level of nestedness.

See also:

[Top]


Member type definitions


Typedef TLoopOwner

typedef TLoop* CActiveScheduler::TLoopOwner;

Description