Class RMsgQueueBase

class RMsgQueueBase : public RHandleBase;

Description

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

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

Members

Defined in RMsgQueueBase:
CancelDataAvailable(), CancelSpaceAvailable(), CreateGlobal(), CreateLocal(), KMaxLength, MessageSize(), NotifyDataAvailable(), NotifySpaceAvailable(), Open(), Open(), OpenGlobal(), Receive(), ReceiveBlocking(), Send(), SendBlocking(), anonymous

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

See also:

• RMsgQueue

IMPORT_C TInt CreateLocal(TInt aSize, TInt aMsgLength, TOwnerType aType=EOwnerProcess);

Description

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

The Kernel side object representing the message queue is unnamed. This means that it is not possible to search for the message queue, and this makes it local to the current process.

By default, any thread in the process can use this handle to access the message queue. However, specifying EOwnerThread as the third parameter to this function means that only the creating thread can use the handle to access the message queue; any other thread in this process that wants to access the message queue must duplicate this handle.

Parameters

TInt aSize The number of message 'slots' in the queue. This must be a positive value, i.e. greater than zero. TInt aMsgLength The size of each message for the queue, this cannot exceed KMaxLength. 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 aMsgLength is not a multiple of 4 bytes, is less than 4, or is greater than KMaxLength.

See also:

• KMaxLength

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

Description

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

The kernel side object representing the message queue is given the name contained in the specified descriptor, which makes it global, i.e. it is visible to all processes. This means that any thread in any process can search for the message queue, and open a handle to it. If the specified name is empty the kernel side object representing the message queue is unnamed and so cannot be opened by name or searched for. It can however be passed to another process as a process parameter or via IPC.

By default, any thread in the process can use this handle to access the message queue. However, specifying EOwnerThread as the fourth parameter to this function, means that only the creating thread can use this handle to access the message queue; any other thread in this process that wants to access the message queue must either duplicate this handle or use OpenGlobal().

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. TInt aMsgLength The size of each message for the queue, this cannot exceed KMaxLength. 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 aMsgLength is not a multiple of 4 bytes, is less than 4, or is greater than KMaxLength.

See also:

• KMaxLength

IMPORT_C TInt OpenGlobal(const TDesC &aName, TOwnerType aType=EOwnerProcess);

Description

Opens a global message queue.

Global message queues are identified by name.

By default, any thread in the process can use this handle to access the message queue. However, specifying EOwnerThread as the second parameter to this function, means that only the opening thread can use this handle to access the message queue; any other thread in this process that wants to access the message queue must either duplicate this handle or use OpenGlobal() again.

Parameters

const TDesC &aName The name of the message queue. TOwnerType aType The type of handle to be created. EOwnerProcess is the default value, if not explicitly specified.

Return value

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

IMPORT_C TInt Open(RMessagePtr2 aMessage, TInt aParam, TOwnerType aType=EOwnerProcess);

Description

Opens a global message queue using a handle passed in a server message.

By default, any thread in the process can use this handle to access the message queue. However, specifying EOwnerThread as the third parameter to this function, means that only the opening thread can use this handle to access the message queue.

Parameters

RMessagePtr2 aMessage The server message. TInt aParam The number of the message parameter which holds the handle. TOwnerType aType The type of handle to be created. EOwnerProcess is the default value, if not explicitly specified.

Return value

TInt

IMPORT_C TInt Open(TInt aArgumentIndex, TOwnerType aType=EOwnerProcess);

Description

Opens a message queue using the handle passed in during process creation.

Parameters

TInt aArgumentIndex The number on the parameter which holds the handle. TOwnerType aType The type of handle to be created. EOwnerProcess is the default value, if not explicitly specified.

Return value

TInt KErrNone, ifsuccessful; KErrArgument, if aArgumentIndex doesn't contain a message queue handle; KErrNotFound, if aArgumentIndex is empty.

IMPORT_C TInt Send(const TAny *aPtr, TInt aLength);

Description

Sends a message through this queue.

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

Note that, once on the queue, the content of the message cannot be accessed other than through a call to Receive() or ReceiveBlocking().

Parameters

const TAny *aPtr A pointer to the message data TInt aLength The length of the message data, this must not exceed the queue's message size.

Return value

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

Panic codes

KERN-EXEC 48 if aLength is greater than the message length specified when the queue was created, or if aLength is less than or equal to zero.

IMPORT_C void SendBlocking(const TAny *aPtr, TInt aLength);

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().

Parameters

const TAny *aPtr A pointer to the message data. TInt aLength The length of the message data, this must not exceed the queue's message size.

Panic codes

KERN-EXEC 48 if aLength is greater than the message length specified when the queue was created, or if aLength is less than or equal to zero.

IMPORT_C TInt Receive(TAny *aPtr, TInt aLength);

Description

Retrieves the first message in the queue.

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

Parameters

TAny *aPtr A pointer to a buffer to receive the message data. TInt aLength The length of the buffer for the message, this must match the queue's message size.

Return value

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

Panic codes

KERN-EXEC 48 if aLength is not equal to the message length specified when the queue was created.

IMPORT_C void ReceiveBlocking(TAny *aPtr, TInt aLength);

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().

Parameters

TAny *aPtr A pointer to a buffer to receive the message data. TInt aLength The length of the buffer for the message, this must match the queue's message size.

Panic codes

KERN-EXEC 48 if aLength is not equal to the message length specified when the queue was created.

IMPORT_C void NotifySpaceAvailable(TRequestStatus &aStatus);

Description

Requests notification when space becomes available in the queue.

This is an asynchronous request that completes when there is at least one 'slot'available in the queue.

A thread can have only one space available notification request outstanding on this message queue. If a second request is made before the first request completes, then the calling thread is panicked.

Parameters

TRequestStatus &aStatus The request status object to be completed when space becomes available.

Panic codes

KERN-EXEC 47 if a second request is made while the first request remains outstanding.

IMPORT_C void CancelSpaceAvailable();

Description

Cancels an outstanding space available notification request.

If the request is not already complete, then it now completes with KErrCancel.

Panic codes

KERN-EXEC 50 if attempting to cancel an outstanding request made by a thread in a different process.

IMPORT_C void NotifyDataAvailable(TRequestStatus &aStatus);

Description

Requests notification when there is at least one message in the queue.

A thread can have only one data available notification request outstanding on this message queue. If a second request is made before the first request completes, then the calling thread is panicked.

Parameters

TRequestStatus &aStatus The request status object to be completed when a message becomes available.

Panic codes

KERN-EXEC 47 if a second request is made while the first request remains outstanding.

IMPORT_C void CancelDataAvailable();

Description

Cancels an outstanding data available notification request.

If the request is not already complete, then it now completes with KErrCancel.

Panic codes

KERN-EXEC 50 if attempting to cancel an outstanding request made by a thread in a different process.

IMPORT_C TInt MessageSize();

Description

Gets the size of message slots in the queue.

Return value

TInt The size of a message slot in the queue.

n/a

Description

The limit for the size of an individual message.

KMaxLength