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/* $Id: once.cpp $ */
/** @file
* IPRT - Execute Once.
*/
/*
* Copyright (C) 2007 Sun Microsystems, Inc.
*
* 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.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
* Clara, CA 95054 USA or visit http://www.sun.com if you need
* additional information or have any questions.
*/
/*******************************************************************************
* Header Files *
*******************************************************************************/
#include <iprt/once.h>
#include "internal/iprt.h"
#include <iprt/semaphore.h>
#include <iprt/thread.h>
#include <iprt/err.h>
#include <iprt/assert.h>
#include <iprt/asm.h>
RTDECL(int) RTOnce(PRTONCE pOnce, PFNRTONCE pfnOnce, void *pvUser1, void *pvUser2)
{
/*
* Validate input (strict builds only).
*/
AssertPtr(pOnce);
AssertPtr(pfnOnce);
/*
* Deal with the 'initialized' case first
*/
int32_t iState = ASMAtomicUoReadS32(&pOnce->iState);
if (RT_LIKELY(iState == 2))
return ASMAtomicUoReadS32(&pOnce->rc);
AssertReturn(iState == -1 || iState == 1, VERR_INTERNAL_ERROR);
/*
* Do we initialize it?
*/
if (iState == -1)
{
RTSEMEVENTMULTI hEventMulti;
int rc = RTSemEventMultiCreate(&hEventMulti);
if (RT_FAILURE(rc))
hEventMulti = NIL_RTSEMEVENTMULTI;
if (ASMAtomicCmpXchgS32(&pOnce->iState, 1, -1))
{
ASMAtomicWriteHandle(&pOnce->hEventMulti, hEventMulti);
ASMAtomicIncS32(&pOnce->cEventRefs);
/* do the execute once stuff. */
int32_t rcOnce = pfnOnce(pvUser1, pvUser2);
/* set the return code, change the state and signal any waiters. */
ASMAtomicWriteS32(&pOnce->rc, rcOnce);
ASMAtomicWriteS32(&pOnce->iState, 2);
if (hEventMulti != NIL_RTSEMEVENTMULTI)
RTSemEventMultiSignal(hEventMulti);
/* last guy destroys the semaphore. */
if (ASMAtomicDecS32(&pOnce->cEventRefs) == 0)
ASMAtomicWriteSize(&pOnce->hEventMulti, NIL_RTSEMEVENTMULTI);
else
hEventMulti = NIL_RTSEMEVENTMULTI;
}
if (hEventMulti != NIL_RTSEMEVENTMULTI)
RTSemEventMultiDestroy(hEventMulti);
}
/*
* Wait for it to finish initializing.
*/
if (ASMAtomicReadS32(&pOnce->iState) == 1)
{
int i = 0;
while (ASMAtomicReadS32(&pOnce->iState) == 1)
{
bool fYieldSleep = true;
/*
* Take care not to increment the counter if it's 0, that indicates
* that RTONCE::hEventMulti isn't valid either because it's not set
* yet, or because it's being destroyed.
*/
int32_t cEventRefs = ASMAtomicUoReadS32(&pOnce->cEventRefs);
while ( cEventRefs > 0
&& !ASMAtomicCmpXchgS32(&pOnce->cEventRefs, cEventRefs + 1, cEventRefs))
cEventRefs = ASMAtomicUoReadS32(&pOnce->cEventRefs);
if (cEventRefs > 1)
{
/*
* The hEventMulti might be NIL for two reasons, see above in
* the init code, if it isn't valid just do the yield/sleep thing.
*/
RTSEMEVENTMULTI hEventMulti;
ASMAtomicUoReadSize(&pOnce->hEventMulti, &hEventMulti);
if (hEventMulti != NIL_RTSEMEVENTMULTI)
{
fYieldSleep = false;
RTSemEventMultiWait(hEventMulti, RT_INDEFINITE_WAIT);
}
/*
* Last thread cleans up.
*/
if (ASMAtomicDecS32(&pOnce->cEventRefs) == 0)
{
ASMAtomicXchgHandle(&pOnce->hEventMulti, NIL_RTSEMEVENTMULTI, &hEventMulti);
if (hEventMulti != NIL_RTSEMEVENTMULTI)
RTSemEventMultiDestroy(hEventMulti);
}
}
/*
* If we didn't block, yield or sleep for a bit.
*
* The sleep is essential to prevent higher priority threads from spinning wildly
* and preventing a lower priority thread from completing the pfnOnce operation
* in a timely manner.
*/
if (fYieldSleep)
{
if (ASMAtomicReadS32(&pOnce->iState) != 1)
break;
if (!(++i % 8) )
RTThreadSleep(1);
else
RTThreadYield();
}
}
}
/*
* Finally, return the status code from the execute once function.
*/
return ASMAtomicUoReadS32(&pOnce->rc);
}
RT_EXPORT_SYMBOL(RTOnce);
RTDECL(void) RTOnceReset(PRTONCE pOnce)
{
/* Cannot be done while busy! */
AssertPtr(pOnce);
Assert(pOnce->hEventMulti == NIL_RTSEMEVENTMULTI);
Assert(pOnce->iState != 1);
/* Do the same as RTONCE_INITIALIZER does. */
ASMAtomicWriteS32(&pOnce->rc, VERR_INTERNAL_ERROR);
ASMAtomicWriteS32(&pOnce->iState, -1);
}
RT_EXPORT_SYMBOL(RTOnceReset);
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