haiku/src/kits/app/MessageQueue.cpp

/*
 * Copyright 2001-2014 Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Authors:
 *		Unknown? Eric?
 *		Axel Dörfler, axeld@pinc-software.de
 */


// Queue for holding BMessages


#include <MessageQueue.h>
#include <Autolock.h>
#include <Message.h>


BMessageQueue::BMessageQueue()
	:
	fHead(NULL),
	fTail(NULL),
	fMessageCount(0),
	fLock("BMessageQueue Lock")
{
}


BMessageQueue::~BMessageQueue()
{
	if (!Lock())
		return;

	BMessage* message = fHead;
	while (message != NULL) {
		BMessage* next = message->fQueueLink;

		delete message;
		message = next;
	}
}


void
BMessageQueue::AddMessage(BMessage* message)
{
	if (message == NULL)
		return;

	BAutolock _(fLock);
	if (!IsLocked())
		return;

	// The message passed in will be the last message on the queue so its
	// link member should be set to null.
	message->fQueueLink = NULL;

	fMessageCount++;

	if (fTail == NULL) {
		// there are no messages in the queue yet
		fHead = fTail = message;
	} else {
		// just add it after the tail
		fTail->fQueueLink = message;
		fTail = message;
	}
}


void
BMessageQueue::RemoveMessage(BMessage* message)
{
	if (message == NULL)
		return;

	BAutolock _(fLock);
	if (!IsLocked())
		return;

	BMessage* last = NULL;
	for (BMessage* entry = fHead; entry != NULL; entry = entry->fQueueLink) {
		if (entry == message) {
			// remove this one
			if (entry == fHead)
				fHead = entry->fQueueLink;
			else
				last->fQueueLink = entry->fQueueLink;

			if (entry == fTail)
				fTail = last;

			fMessageCount--;
			return;
		}
		last = entry;
	}
}


int32
BMessageQueue::CountMessages() const
{
    return fMessageCount;
}


bool
BMessageQueue::IsEmpty() const
{
    return fMessageCount == 0;
}


BMessage*
BMessageQueue::FindMessage(int32 index) const
{
	BAutolock _(fLock);
	if (!IsLocked())
		return NULL;

	if (index < 0 || index >= fMessageCount)
		return NULL;

	for (BMessage* message = fHead; message != NULL; message = message->fQueueLink) {
		// If the index reaches zero, then we have found a match.
		if (index == 0)
			return message;

		index--;
	}

    return NULL;
}


BMessage*
BMessageQueue::FindMessage(uint32 what, int32 index) const
{
	BAutolock _(fLock);
	if (!IsLocked())
		return NULL;

	if (index < 0 || index >= fMessageCount)
		return NULL;

	for (BMessage* message = fHead; message != NULL; message = message->fQueueLink) {
		if (message->what == what) {
			// If the index reaches zero, then we have found a match.
			if (index == 0)
				return message;

			index--;
		}
	}

    return NULL;
}


bool
BMessageQueue::Lock()
{
    return fLock.Lock();
}


void
BMessageQueue::Unlock()
{
	fLock.Unlock();
}


bool
BMessageQueue::IsLocked() const
{
	return fLock.IsLocked();
}


BMessage*
BMessageQueue::NextMessage()
{
	BAutolock _(fLock);
	if (!IsLocked())
		return NULL;

	// remove the head of the queue, if any, and return it

	BMessage* head = fHead;
	if (head == NULL)
		return NULL;

	fMessageCount--;
	fHead = head->fQueueLink;

	if (fHead == NULL) {
		// If the queue is empty after removing the front element,
		// we need to set the tail of the queue to NULL since the queue
		// is now empty.
		fTail = NULL;
	}

	return head;
}


bool
BMessageQueue::IsNextMessage(const BMessage* message) const
{
	BAutolock _(fLock);
	return fHead == message;
}


// This method is only here for R5 binary compatibility!
// It should be dropped as soon as possible (it misses the const qualifier).
bool
BMessageQueue::IsLocked()
{
	return fLock.IsLocked();
}


void BMessageQueue::_ReservedMessageQueue1() {}
void BMessageQueue::_ReservedMessageQueue2() {}
void BMessageQueue::_ReservedMessageQueue3() {}