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/* $Id: once.cpp $ */
/** @file
* IPRT - Execute Once.
*/
/*
* Copyright (C) 2007 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/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>
/**
* The state loop of the other threads.
*
* @returns VINF_SUCCESS when everything went smoothly. IPRT status code if we
* encountered trouble.
* @param pOnce The execute once structure.
* @param phEvtM Where to store the semaphore handle so the caller
* can do the cleaning up for us.
*/
static int rtOnceOtherThread(PRTONCE pOnce, PRTSEMEVENTMULTI phEvtM)
{
uint32_t cYields = 0;
for (;;)
{
int32_t iState = ASMAtomicReadS32(&pOnce->iState);
switch (iState)
{
/*
* No semaphore, try create one.
*/
case RTONCESTATE_BUSY_NO_SEM:
if (ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_BUSY_CREATING_SEM, RTONCESTATE_BUSY_NO_SEM))
{
int rc = RTSemEventMultiCreate(phEvtM);
if (RT_SUCCESS(rc))
{
ASMAtomicWriteHandle(&pOnce->hEventMulti, *phEvtM);
int32_t cRefs = ASMAtomicIncS32(&pOnce->cEventRefs); Assert(cRefs == 1); NOREF(cRefs);
if (!ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_BUSY_HAVE_SEM, RTONCESTATE_BUSY_CREATING_SEM))
{
/* Too slow. */
AssertReturn(ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_DONE, RTONCESTATE_DONE_CREATING_SEM)
, VERR_INTERNAL_ERROR_5);
ASMAtomicWriteHandle(&pOnce->hEventMulti, NIL_RTSEMEVENTMULTI);
cRefs = ASMAtomicDecS32(&pOnce->cEventRefs); Assert(cRefs == 0);
RTSemEventMultiDestroy(*phEvtM);
*phEvtM = NIL_RTSEMEVENTMULTI;
}
}
else
{
AssertReturn( ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_BUSY_SPIN, RTONCESTATE_BUSY_CREATING_SEM)
|| ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_DONE, RTONCESTATE_DONE_CREATING_SEM)
, VERR_INTERNAL_ERROR_4);
*phEvtM = NIL_RTSEMEVENTMULTI;
}
}
break;
/*
* This isn't nice, but it's the easy way out.
*/
case RTONCESTATE_BUSY_CREATING_SEM:
case RTONCESTATE_BUSY_SPIN:
cYields++;
if (!(++cYields % 8))
RTThreadSleep(1);
else
RTThreadYield();
break;
/*
* There is a semaphore, try wait on it.
*
* We continue waiting after reaching DONE_HAVE_SEM if we
* already got the semaphore to avoid racing the first thread.
*/
case RTONCESTATE_DONE_HAVE_SEM:
if (*phEvtM == NIL_RTSEMEVENTMULTI)
return VINF_SUCCESS;
/* fall thru */
case RTONCESTATE_BUSY_HAVE_SEM:
{
/*
* Grab the semaphore if we haven't got it yet.
* We must take care not to increment the counter if it
* is 0. This may happen if we're racing a state change.
*/
if (*phEvtM == NIL_RTSEMEVENTMULTI)
{
int32_t cEventRefs = ASMAtomicUoReadS32(&pOnce->cEventRefs);
while ( cEventRefs > 0
&& ASMAtomicUoReadS32(&pOnce->iState) == RTONCESTATE_BUSY_HAVE_SEM)
{
if (ASMAtomicCmpXchgExS32(&pOnce->cEventRefs, cEventRefs + 1, cEventRefs, &cEventRefs))
break;
ASMNopPause();
}
if (cEventRefs <= 0)
break;
ASMAtomicReadHandle(&pOnce->hEventMulti, phEvtM);
AssertReturn(*phEvtM != NIL_RTSEMEVENTMULTI, VERR_INTERNAL_ERROR_2);
}
/*
* We've got a sempahore, do the actual waiting.
*/
do
RTSemEventMultiWaitNoResume(*phEvtM, RT_INDEFINITE_WAIT);
while (ASMAtomicReadS32(&pOnce->iState) == RTONCESTATE_BUSY_HAVE_SEM);
break;
}
case RTONCESTATE_DONE_CREATING_SEM:
case RTONCESTATE_DONE:
return VINF_SUCCESS;
default:
AssertMsgFailedReturn(("%d\n", iState), VERR_INTERNAL_ERROR_3);
}
}
}
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 == RTONCESTATE_DONE
|| iState == RTONCESTATE_DONE_CREATING_SEM
|| iState == RTONCESTATE_DONE_HAVE_SEM
))
return ASMAtomicUoReadS32(&pOnce->rc);
AssertReturn( iState == RTONCESTATE_UNINITIALIZED
|| iState == RTONCESTATE_BUSY_NO_SEM
|| iState == RTONCESTATE_BUSY_SPIN
|| iState == RTONCESTATE_BUSY_CREATING_SEM
|| iState == RTONCESTATE_BUSY_HAVE_SEM
, VERR_INTERNAL_ERROR);
/*
* Do we initialize it?
*/
int32_t rcOnce;
if ( iState == RTONCESTATE_UNINITIALIZED
&& ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_BUSY_NO_SEM, RTONCESTATE_UNINITIALIZED))
{
/*
* Yes, so do the execute once stuff.
*/
rcOnce = pfnOnce(pvUser1, pvUser2);
ASMAtomicWriteS32(&pOnce->rc, rcOnce);
/*
* If there is a sempahore to signal, we're in for some extra work here.
*/
if ( !ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_DONE, RTONCESTATE_BUSY_NO_SEM)
&& !ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_DONE, RTONCESTATE_BUSY_SPIN)
&& !ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_DONE_CREATING_SEM, RTONCESTATE_BUSY_CREATING_SEM)
)
{
/* Grab the sempahore by switching to 'DONE_HAVE_SEM' before reaching 'DONE'. */
AssertReturn(ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_DONE_HAVE_SEM, RTONCESTATE_BUSY_HAVE_SEM),
VERR_INTERNAL_ERROR_2);
int32_t cRefs = ASMAtomicIncS32(&pOnce->cEventRefs);
Assert(cRefs > 1);
RTSEMEVENTMULTI hEvtM;
ASMAtomicReadHandle(&pOnce->hEventMulti, &hEvtM);
Assert(hEvtM != NIL_RTSEMEVENTMULTI);
ASMAtomicWriteS32(&pOnce->iState, RTONCESTATE_DONE);
/* Signal it and return. */
RTSemEventMultiSignal(hEvtM);
}
}
else
{
/*
* Wait for the first thread to complete. Delegate this to a helper
* function to simplify cleanup and keep things a bit shorter.
*/
RTSEMEVENTMULTI hEvtM = NIL_RTSEMEVENTMULTI;
rcOnce = rtOnceOtherThread(pOnce, &hEvtM);
if (hEvtM != NIL_RTSEMEVENTMULTI)
{
if (ASMAtomicDecS32(&pOnce->cEventRefs) == 0)
{
bool fRc;
ASMAtomicCmpXchgHandle(&pOnce->hEventMulti, NIL_RTSEMEVENTMULTI, hEvtM, fRc); Assert(fRc);
fRc = ASMAtomicCmpXchgS32(&pOnce->iState, RTONCESTATE_DONE, RTONCESTATE_DONE_HAVE_SEM); Assert(fRc);
RTSemEventMultiDestroy(hEvtM);
}
}
if (RT_SUCCESS(rcOnce))
rcOnce = ASMAtomicUoReadS32(&pOnce->rc);
}
return rcOnce;
}
RT_EXPORT_SYMBOL(RTOnce);
RTDECL(void) RTOnceReset(PRTONCE pOnce)
{
/* Cannot be done while busy! */
AssertPtr(pOnce);
Assert(pOnce->hEventMulti == NIL_RTSEMEVENTMULTI);
int32_t iState = ASMAtomicUoReadS32(&pOnce->iState);
AssertMsg( iState == RTONCESTATE_DONE
&& iState == RTONCESTATE_UNINITIALIZED,
("%d\n", iState));
/* Do the same as RTONCE_INITIALIZER does. */
ASMAtomicWriteS32(&pOnce->rc, VERR_INTERNAL_ERROR);
ASMAtomicWriteS32(&pOnce->iState, RTONCESTATE_UNINITIALIZED);
}
RT_EXPORT_SYMBOL(RTOnceReset);
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