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# BMessageQueue

Derived from: none

Declared in: be/app/MessageQueue.h

Library: libbe.so

###### Summary

The BMessageQueue class completes the implementation of BLooper by providing a first-in/first-out stack in which the looper can place in-coming BMessages. In general, the message dispatching mechanism of BLooper should suffice. However, if you ever need to manipulate a BMessage queue directly, you can do so.

## Constructor and Destructor

### BMessageQueue()

`BMessageQueue(`void`)`

Creates an empty BMessageQueue object.

### ~BMessageQueue()

virtual `~BMessageQueue()`

Deletes all the objects in the queue and all the data structures used to manage the queue.

## Member Functions

### AddMessage() , RemoveMessage()

void `AddMessage(`BMessage *message`)`
void `RemoveMessage(`BMessage *message`)`

`AddMessage()` adds message to the far end of the queue. `RemoveMessage()` removes a particular message from the queue and deletes it.

### CountMessages() , IsEmpty()

int32 `CountMessages(`void`)` const
bool `IsEmpty(`void`)` const

`CountMessages()` returns the number of messages currently in the queue.

`IsEmpty()` returns `true` if the object doesn't contain any messages, and `false` otherwise.

### FindMessage()

BMessage *`FindMessage(`int32 index`)` const
BMessage *`FindMessage(`uint32 what, int32 index = 0`)` const

`FindMessage()` returns a pointer to the index'th BMessage in the queue, where index 0 signifies the message that's been in the queue the longest. The second version lets you specify a what field value; in this case, only messages that match the what argument are counted. If no message matches the criteria, the functions return `NULL`.

The message is not removed from the message queue.

### IsEmpty() see CountMessages()

### Lock() , Unlock()

bool `Lock(`void`)`
void `Unlock(`void`)`

These functions lock and unlock the BMessageQueue, so that another thread won't alter the contents of the queue while it's being read. `Lock()` doesn't return until it has the queue locked; it always returns `true`. `Unlock()` releases the lock so that someone else can lock it. Calls to these functions can be nested.

See also: `BLooper::Lock()`

### NextMessage()

BMessage *`NextMessage(`void`)`

Removes and returns the oldest message from the queue. If the queue is empty, the function returns `NULL`.

See also: `FindMessage()`

### RemoveMessage() see AddMessage()

### Unlock() see Lock()

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