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+/** @file
+ * IPRT - Execute Once.
+ */
+
+/*
+ * Copyright (C) 2006-2022 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 */
+