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/** @file
* IPRT - Generic Work Queue with concurrent atomic access.
*/
/*
* Copyright (C) 2013-2025 Oracle and/or its affiliates.
*
* This file is part of VirtualBox base platform packages, as
* available from https://www.virtualbox.org.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, in version 3 of the
* License.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <https://www.gnu.org/licenses>.
*
* The contents of this file may alternatively be used under the terms
* of the Common Development and Distribution License Version 1.0
* (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
* in the VirtualBox distribution, in which case the provisions of the
* CDDL are applicable instead of those of the GPL.
*
* You may elect to license modified versions of this file under the
* terms and conditions of either the GPL or the CDDL or both.
*
* SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
*/
#ifndef IPRT_INCLUDED_queueatomic_h
#define IPRT_INCLUDED_queueatomic_h
#ifndef RT_WITHOUT_PRAGMA_ONCE
# pragma once
#endif
#include <iprt/types.h>
#include <iprt/asm.h>
/** @defgroup grp_rt_queueatomic RTQueueAtomic - Generic Work Queue
* @ingroup grp_rt
*
* Implementation of a lockless work queue for threaded environments.
* @{
*/
RT_C_DECLS_BEGIN
/**
* A work item
*/
typedef struct RTQUEUEATOMICITEM
{
/** Pointer to the next work item in the list. */
struct RTQUEUEATOMICITEM * volatile pNext;
} RTQUEUEATOMICITEM;
/** Pointer to a work item. */
typedef RTQUEUEATOMICITEM *PRTQUEUEATOMICITEM;
/** Pointer to a work item pointer. */
typedef PRTQUEUEATOMICITEM *PPRTQUEUEATOMICITEM;
/**
* Work queue.
*/
typedef struct RTQUEUEATOMIC
{
/* Head of the work queue. */
volatile PRTQUEUEATOMICITEM pHead;
} RTQUEUEATOMIC;
/** Pointer to a work queue. */
typedef RTQUEUEATOMIC *PRTQUEUEATOMIC;
/**
* Initialize a work queue.
*
* @param pWorkQueue Pointer to an unitialised work queue.
*/
DECLINLINE(void) RTQueueAtomicInit(PRTQUEUEATOMIC pWorkQueue)
{
ASMAtomicWriteNullPtr(&pWorkQueue->pHead);
}
/**
* Insert a new item into the work queue.
*
* @param pWorkQueue The work queue to insert into.
* @param pItem The item to insert.
*/
DECLINLINE(void) RTQueueAtomicInsert(PRTQUEUEATOMIC pWorkQueue, PRTQUEUEATOMICITEM pItem)
{
PRTQUEUEATOMICITEM pNext = ASMAtomicUoReadPtrT(&pWorkQueue->pHead, PRTQUEUEATOMICITEM);
PRTQUEUEATOMICITEM pHeadOld;
pItem->pNext = pNext;
while (!ASMAtomicCmpXchgExPtr(&pWorkQueue->pHead, pItem, pNext, &pHeadOld))
{
pNext = pHeadOld;
Assert(pNext != pItem);
pItem->pNext = pNext;
ASMNopPause();
}
}
/**
* Remove all items from the given work queue and return them in the inserted order.
*
* @returns Pointer to the first item.
* @param pWorkQueue The work queue.
*/
DECLINLINE(PRTQUEUEATOMICITEM) RTQueueAtomicRemoveAll(PRTQUEUEATOMIC pWorkQueue)
{
PRTQUEUEATOMICITEM pHead = ASMAtomicXchgPtrT(&pWorkQueue->pHead, NULL, PRTQUEUEATOMICITEM);
/* Reverse it. */
PRTQUEUEATOMICITEM pCur = pHead;
pHead = NULL;
while (pCur)
{
PRTQUEUEATOMICITEM pInsert = pCur;
pCur = pCur->pNext;
pInsert->pNext = pHead;
pHead = pInsert;
}
return pHead;
}
RT_C_DECLS_END
/** @} */
#endif /* !IPRT_INCLUDED_queueatomic_h */
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