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/** @file
* IPRT - Execute Once.
*/
/*
* Copyright (C) 2006-2007 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.
*/
#ifndef ___iprt_once_h
#define ___iprt_once_h
#include <iprt/cdefs.h>
#include <iprt/types.h>
#include <iprt/asm.h>
#include <iprt/err.h>
RT_C_DECLS_BEGIN
/** @defgroup grp_rt_once RTOnce - Execute Once
* @ingroup grp_rt
* @{
*/
/**
* Execute once structure.
*
* This is typically a global variable that is statically initialized
* by RTONCE_INITIALIZER.
*/
typedef struct RTONCE
{
/** Event semaphore that the other guys are blocking on. */
RTSEMEVENTMULTI volatile hEventMulti;
/** Reference counter for hEventMulti. */
int32_t volatile cEventRefs;
/** -1 when uninitialized, 1 when initializing (busy) and 2 when done. */
int32_t volatile iState;
/** The return code of pfnOnce. */
int32_t volatile rc;
} RTONCE;
/** Pointer to a execute once struct. */
typedef RTONCE *PRTONCE;
/**
* The execute once statemachine.
*/
typedef enum RTONCESTATE
{
/** RTOnce() has not been called.
* Next: NO_SEM */
RTONCESTATE_UNINITIALIZED = 1,
/** RTOnce() is busy, no race.
* Next: CREATING_SEM, DONE */
RTONCESTATE_BUSY_NO_SEM,
/** More than one RTOnce() caller is busy.
* Next: BUSY_HAVE_SEM, BUSY_SPIN, DONE_CREATING_SEM, DONE */
RTONCESTATE_BUSY_CREATING_SEM,
/** More than one RTOnce() caller, the first is busy, the others are
* waiting.
* Next: DONE */
RTONCESTATE_BUSY_HAVE_SEM,
/** More than one RTOnce() caller, the first is busy, the others failed to
* create a semaphore and are spinning.
* Next: DONE */
RTONCESTATE_BUSY_SPIN,
/** More than one RTOnce() caller, the first has completed, the others
* are busy creating the semaphore.
* Next: DONE_HAVE_SEM */
RTONCESTATE_DONE_CREATING_SEM,
/** More than one RTOnce() caller, the first is busy grabbing the
* semaphore, while the others are waiting.
* Next: DONE */
RTONCESTATE_DONE_HAVE_SEM,
/** The execute once stuff has completed. */
RTONCESTATE_DONE = 16
} RTONCESTATE;
/** Static initializer for RTONCE variables. */
#define RTONCE_INITIALIZER { NIL_RTSEMEVENTMULTI, 0, RTONCESTATE_UNINITIALIZED, VERR_INTERNAL_ERROR }
/**
* Callback that gets executed once.
*
* @returns IPRT style status code, RTOnce returns this.
*
* @param pvUser1 The first user parameter.
* @param pvUser2 The second user parameter.
*/
typedef DECLCALLBACK(int32_t) FNRTONCE(void *pvUser1, void *pvUser2);
/** Pointer to a FNRTONCE. */
typedef FNRTONCE *PFNRTONCE;
/**
* Serializes execution of the pfnOnce function, making sure it's
* executed exactly once and that nobody returns from RTOnce before
* it has executed successfully.
*
* @returns IPRT like status code returned by pfnOnce.
*
* @param pOnce Pointer to the execute once variable.
* @param pfnOnce The function to executed once.
* @param pvUser1 The first user parameter for pfnOnce.
* @param pvUser2 The second user parameter for pfnOnce.
*/
RTDECL(int) RTOnceSlow(PRTONCE pOnce, PFNRTONCE pfnOnce, void *pvUser1, void *pvUser2);
/**
* Serializes execution of the pfnOnce function, making sure it's
* executed exactly once and that nobody returns from RTOnce before
* it has executed successfully.
*
* @returns IPRT like status code returned by pfnOnce.
*
* @param pOnce Pointer to the execute once variable.
* @param pfnOnce The function to executed once.
* @param pvUser1 The first user parameter for pfnOnce.
* @param pvUser2 The second user parameter for pfnOnce.
*/
DECLINLINE(int) RTOnce(PRTONCE pOnce, PFNRTONCE pfnOnce, void *pvUser1, void *pvUser2)
{
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);
return RTOnceSlow(pOnce, pfnOnce, pvUser1, pvUser2);
}
/**
* Resets an execute once variable.
*
* The caller is responsible for making sure there are no concurrent accesses to
* the execute once variable.
*
* @param pOnce Pointer to the execute once variable.
*/
RTDECL(void) RTOnceReset(PRTONCE pOnce);
/** @} */
RT_C_DECLS_END
#endif
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