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/** @file
* IPRT - Execute Once.
*/
/*
* Copyright (C) 2006-2025 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_once_h
#define IPRT_INCLUDED_once_h
#ifndef RT_WITHOUT_PRAGMA_ONCE
# pragma once
#endif
#include <iprt/cdefs.h>
#include <iprt/types.h>
#include <iprt/asm.h>
#include <iprt/errcore.h>
#include <iprt/list.h>
RT_C_DECLS_BEGIN
/** @defgroup grp_rt_once RTOnce - Execute Once
* @ingroup grp_rt
* @{
*/
/**
* Callback that gets executed once.
*
* @returns IPRT style status code, RTOnce returns this.
*
* @param pvUser The user parameter.
*/
typedef DECLCALLBACKTYPE(int32_t, FNRTONCE,(void *pvUser));
/** Pointer to a FNRTONCE. */
typedef FNRTONCE *PFNRTONCE;
/**
* Callback that gets executed on IPRT/process termination.
*
* @param pvUser The user parameter.
* @param fLazyCleanUpOk Indicates whether lazy clean-up is OK (see
* initterm.h).
*/
typedef DECLCALLBACKTYPE(void, FNRTONCECLEANUP,(void *pvUser, bool fLazyCleanUpOk));
/** Pointer to a FNRTONCE. */
typedef FNRTONCECLEANUP *PFNRTONCECLEANUP;
/**
* 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;
/** See RTONCESTATE. */
int32_t volatile iState;
/** The return code of pfnOnce. */
int32_t volatile rc;
/** Pointer to the clean-up function. */
PFNRTONCECLEANUP pfnCleanUp;
/** Argument to hand to the clean-up function. */
void *pvUser;
/** Clean-up list entry. */
RTLISTNODE CleanUpNode;
} 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, NULL, NULL, { NULL, NULL } }
/**
* 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 pfnCleanUp The function that will be doing the cleaning up.
* Optional.
* @param pvUser The user parameter for pfnOnce.
*/
RTDECL(int) RTOnceSlow(PRTONCE pOnce, PFNRTONCE pfnOnce, FNRTONCECLEANUP pfnCleanUp, void *pvUser);
/**
* 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 pvUser The user parameter for pfnOnce.
*/
DECLINLINE(int) RTOnce(PRTONCE pOnce, PFNRTONCE pfnOnce, void *pvUser)
{
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, NULL, pvUser);
}
/**
* Execute pfnOnce once and register a termination clean-up callback.
*
* 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 pfnCleanUp The function that will be doing the cleaning up.
* @param pvUser The user parameter for pfnOnce.
*/
DECLINLINE(int) RTOnceEx(PRTONCE pOnce, PFNRTONCE pfnOnce, PFNRTONCECLEANUP pfnCleanUp, void *pvUser)
{
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, pfnCleanUp, pvUser);
}
/**
* 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);
/**
* Check whether the execute once variable was successfullly initialized.
*/
DECLINLINE(bool) RTOnceWasInitialized(PRTONCE pOnce)
{
int32_t const iState = ASMAtomicUoReadS32(&pOnce->iState);
int32_t const rc = ASMAtomicUoReadS32(&pOnce->rc);
return RT_SUCCESS(rc)
&& ( iState == RTONCESTATE_DONE
|| iState == RTONCESTATE_DONE_CREATING_SEM
|| iState == RTONCESTATE_DONE_HAVE_SEM);
}
/** @} */
RT_C_DECLS_END
#endif /* !IPRT_INCLUDED_once_h */
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