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/* $Id: circbuf.cpp $ */
/** @file
* IPRT - Lock Free Circular Buffer
*/
/*
* Copyright (C) 2011-2019 Oracle Corporation
*
* This file is part of VirtualBox Open Source Edition (OSE), as
* available from http://www.virtualbox.org. This file is free software;
* you can redistribute it and/or modify it under the terms of the GNU
* General Public License (GPL) as published by the Free Software
* Foundation, in version 2 as it comes in the "COPYING" file of the
* VirtualBox OSE distribution. VirtualBox OSE is distributed in the
* hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
*
* The contents of this file may alternatively be used under the terms
* of the Common Development and Distribution License Version 1.0
* (CDDL) only, as it comes in the "COPYING.CDDL" file of the
* VirtualBox OSE 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.
*/
/*********************************************************************************************************************************
* Header Files *
*********************************************************************************************************************************/
#include <iprt/circbuf.h>
#include <iprt/mem.h>
#include <iprt/assert.h>
#include <iprt/asm.h>
#include <iprt/errcore.h>
/*********************************************************************************************************************************
* Structures and Typedefs *
*********************************************************************************************************************************/
/** @todo r=bird: this is missing docs and magic. */
typedef struct RTCIRCBUF
{
/** The current read position in the buffer. */
size_t offRead;
/** Is a read block acquired currently? */
bool fReading;
/** Is a write block acquired currently? */
bool fWriting;
/** The current write position in the buffer. */
size_t offWrite;
/** How much space of the buffer is currently in use. */
volatile size_t cbUsed;
/** How big is the buffer. */
size_t cbBuf;
/** The buffer itself. */
void *pvBuf;
} RTCIRCBUF, *PRTCIRCBUF;
RTDECL(int) RTCircBufCreate(PRTCIRCBUF *ppBuf, size_t cbSize)
{
/* Validate input. */
AssertPtrReturn(ppBuf, VERR_INVALID_POINTER);
AssertReturn(cbSize > 0, VERR_INVALID_PARAMETER);
PRTCIRCBUF pTmpBuf;
pTmpBuf = (PRTCIRCBUF)RTMemAllocZ(sizeof(RTCIRCBUF));
if (!pTmpBuf)
return VERR_NO_MEMORY;
pTmpBuf->pvBuf = RTMemAlloc(cbSize);
if (pTmpBuf->pvBuf)
{
pTmpBuf->cbBuf = cbSize;
*ppBuf = pTmpBuf;
return VINF_SUCCESS;
}
RTMemFree(pTmpBuf);
return VERR_NO_MEMORY;
}
RTDECL(void) RTCircBufDestroy(PRTCIRCBUF pBuf)
{
/* Validate input. */
if (!pBuf)
return;
AssertPtr(pBuf);
RTMemFree(pBuf->pvBuf);
RTMemFree(pBuf);
}
RTDECL(void) RTCircBufReset(PRTCIRCBUF pBuf)
{
/* Validate input. */
AssertPtr(pBuf);
pBuf->offRead = 0;
pBuf->offWrite = 0;
pBuf->cbUsed = 0;
pBuf->fReading = false;
pBuf->fWriting = false;
}
RTDECL(size_t) RTCircBufFree(PRTCIRCBUF pBuf)
{
/* Validate input. */
AssertPtrReturn(pBuf, 0);
return pBuf->cbBuf - ASMAtomicReadZ(&pBuf->cbUsed);
}
RTDECL(size_t) RTCircBufUsed(PRTCIRCBUF pBuf)
{
/* Validate input. */
AssertPtrReturn(pBuf, 0);
return ASMAtomicReadZ(&pBuf->cbUsed);
}
RTDECL(size_t) RTCircBufSize(PRTCIRCBUF pBuf)
{
/* Validate input. */
AssertPtrReturn(pBuf, 0);
return pBuf->cbBuf;
}
RTDECL(bool) RTCircBufIsReading(PRTCIRCBUF pBuf)
{
/* Validate input. */
AssertPtrReturn(pBuf, 0);
return ASMAtomicReadBool(&pBuf->fReading);
}
RTDECL(bool) RTCircBufIsWriting(PRTCIRCBUF pBuf)
{
/* Validate input. */
AssertPtrReturn(pBuf, 0);
return ASMAtomicReadBool(&pBuf->fWriting);
}
RTDECL(size_t) RTCircBufOffsetRead(PRTCIRCBUF pBuf)
{
/* Validate input. */
AssertPtrReturn(pBuf, 0);
return ASMAtomicReadZ(&pBuf->offRead);
}
RTDECL(size_t) RTCircBufOffsetWrite(PRTCIRCBUF pBuf)
{
/* Validate input. */
AssertPtrReturn(pBuf, 0);
return ASMAtomicReadZ(&pBuf->offWrite);
}
RTDECL(void) RTCircBufAcquireReadBlock(PRTCIRCBUF pBuf, size_t cbReqSize, void **ppvStart, size_t *pcbSize)
{
/* Validate input. */
AssertPtr(pBuf);
Assert(cbReqSize > 0);
AssertPtr(ppvStart);
AssertPtr(pcbSize);
*ppvStart = 0;
*pcbSize = 0;
/* How much is in use? */
size_t cbUsed = ASMAtomicReadZ(&pBuf->cbUsed);
if (cbUsed > 0)
{
/* Get the size out of the requested size, the read block till the end
* of the buffer & the currently used size. */
size_t cbSize = RT_MIN(cbReqSize, RT_MIN(pBuf->cbBuf - pBuf->offRead, cbUsed));
if (cbSize > 0)
{
/* Return the pointer address which point to the current read
* position. */
*ppvStart = (char *)pBuf->pvBuf + pBuf->offRead;
*pcbSize = cbSize;
ASMAtomicWriteBool(&pBuf->fReading, true);
}
}
}
RTDECL(void) RTCircBufReleaseReadBlock(PRTCIRCBUF pBuf, size_t cbSize)
{
/* Validate input. */
AssertPtr(pBuf);
/* Split at the end of the buffer. */
pBuf->offRead = (pBuf->offRead + cbSize) % pBuf->cbBuf;
ASMAtomicSubZ(&pBuf->cbUsed, cbSize);
ASMAtomicWriteBool(&pBuf->fReading, false);
}
RTDECL(void) RTCircBufAcquireWriteBlock(PRTCIRCBUF pBuf, size_t cbReqSize, void **ppvStart, size_t *pcbSize)
{
/* Validate input. */
AssertPtr(pBuf);
Assert(cbReqSize > 0);
AssertPtr(ppvStart);
AssertPtr(pcbSize);
*ppvStart = 0;
*pcbSize = 0;
/* How much is free? */
size_t cbFree = pBuf->cbBuf - ASMAtomicReadZ(&pBuf->cbUsed);
if (cbFree > 0)
{
/* Get the size out of the requested size, then write block till the end
* of the buffer & the currently free size. */
size_t cbSize = RT_MIN(cbReqSize, RT_MIN(pBuf->cbBuf - pBuf->offWrite, cbFree));
if (cbSize > 0)
{
/* Return the pointer address which point to the current write
* position. */
*ppvStart = (char*)pBuf->pvBuf + pBuf->offWrite;
*pcbSize = cbSize;
ASMAtomicWriteBool(&pBuf->fWriting, true);
}
}
}
RTDECL(void) RTCircBufReleaseWriteBlock(PRTCIRCBUF pBuf, size_t cbSize)
{
/* Validate input. */
AssertPtr(pBuf);
/* Split at the end of the buffer. */
pBuf->offWrite = (pBuf->offWrite + cbSize) % pBuf->cbBuf;
ASMAtomicAddZ(&pBuf->cbUsed, cbSize);
ASMAtomicWriteBool(&pBuf->fWriting, false);
}
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