Class RMsgQueue

class RMsgQueue : public RMsgQueueBase;

Description

A handle to a message queue.

The templated class provides the behaviour for managing an asynchronous queue of messages, where the template parameter defines the message type.

The class adds a type-checking interface to the basic message queue functionality provided by RMsgQueueBase.

Derivation

• RHandleBase - A handle to an object

• RMsgQueueBase - Provides implementation for managing an asynchronous message queue, and is a base class for the RMsgQueue templated class

• RMsgQueue - A handle to a message queue

Members

Defined in RMsgQueue:
CreateGlobal(), CreateLocal(), Receive(), ReceiveBlocking(), Send(), SendBlocking()

Inherited from RHandleBase:
Attributes(), Close(), Duplicate(), FullName(), Handle(), HandleInfo(), Name(), SetHandle(), SetHandleNC(), SetReturnedHandle(), iHandle

Inherited from RMsgQueueBase:
CancelDataAvailable(), CancelSpaceAvailable(), KMaxLength, MessageSize(), NotifyDataAvailable(), NotifySpaceAvailable(), Open(), OpenGlobal(), anonymous

inline TInt CreateLocal(TInt aSize, TOwnerType aType=EOwnerProcess);

Description

Creates a message queue that is private to the current process, and opens a handle to that message queue.

The size of each message in the queue is the size of the template parameter type. This must conform to the restrictions imposed on the aMsgLength parameter passed to the base class function RMsgQueueBase::CreateLocal().

Parameters

TInt aSize The number of message 'slots' in the queue. This must be a positive value, i.e. greater than zero. TOwnerType aType The type of handle to be created. EOwnerProcess is the default value, if not explicitly specified.

Return value

TInt KErrNone if the queue is created sucessfully, otherwise one of the other system wide error codes.

Panic codes

KERN-EXEC 49 if aSize is less than or equal to zero. KERN-EXEC 48 if the size of the template parameter type is not a multiple of 4 bytes, is less than 4, or is greater than KMaxLength.

inline TInt CreateGlobal(const TDesC &aName, TInt aSize, TOwnerType aType=EOwnerProcess);

Description

Creates a global message queue, and opens a handle to that message queue.

If the name is non-empty, the message queue is visible to all processes. If the name is empty it cannot be opened or searched for by name, but a handle to it can be passed to another process as a process parameter or via IPC.

The size of each message in the queue is the size of the template parameter type. This must conform to the restrictions imposed on the aMsgLength parameter passed to the base class function RMsgQueueBase::CreateGlobal().

Parameters

const TDesC &aName The name to be assigned to the message queue. TInt aSize The number of message 'slots' in the queue. This must be a positive value, i.e. greater than zero. TOwnerType aType The type of handle to be created. EOwnerProcess is the default value, if not explicitly specified.

Return value

TInt KErrNone if the queue is created sucessfully, otherwise one of the other system wide error codes.

Panic codes

KERN-EXEC 49 if aSize is less than or equal to zero. KERN-EXEC 48 if the size of the template parameter type is not a multiple of 4 bytes, is less than 4, or is greater than KMaxLength.

inline TInt Send(const T &aMsg);

Description

Sends a message through this queue.

The function does not wait (i.e. block), if the queue is full.

The function is implemented through a call to RMsgQueueBase::Send().

Parameters

const T &aMsg The message data to be sent.

Return value

TInt KErrNone, if successful; KErrOverflow, if queue is full,

inline void SendBlocking(const T &aMsg);

Description

Sends a message through this queue, and waits for space to become available if the queue is full.

The function uses NotifySpaceAvailable() to provide the blocking operation. Note that it is not possible to cancel a call to SendBlocking().

The function is implemented through a call to RMsgQueueBase::SendBlocking().

Parameters

const T &aMsg The message data to be sent.

inline TInt Receive(T &aMsg);

Description

Retrieves the first message in the queue.

The function does not wait (i.e. block), if the queue is empty.

The function is implemented through a call to RMsgQueueBase::Receive().

Parameters

T &aMsg The object into which the message is retrieved.

Return value

TInt KErrNone, ifsuccessful; KErrUnderflow, if the queue is empty.

inline void ReceiveBlocking(T &aMsg);

Description

Retrieves the first message in the queue, and waits if the queue is empty.

The function uses NotifyDataAvailable() to provide the blocking operation. Note it is not possible to cancel a call to ReceiveBlocking().

The function is implemented through a call to RMsgQueueBase::ReceiveBlocking().

Parameters

T &aMsg The object into which the message is retrieved.