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+/** @file
+ * IPRT - Semaphore.
+ */
+
+/*
+ * 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_semaphore_h
+#define IPRT_INCLUDED_semaphore_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#include <iprt/cdefs.h>
+#include <iprt/types.h>
+#if defined(RT_LOCK_STRICT_ORDER) && defined(IN_RING3)
+# include <iprt/lockvalidator.h>
+#endif
+
+
+RT_C_DECLS_BEGIN
+
+/** @defgroup grp_rt_sems RTSem - Semaphores
+ *
+ * This module implements all kinds of event and mutex semaphores; in addition
+ * to these, IPRT implements "critical sections", which are fast recursive
+ * mutexes (see @ref grp_rt_critsect ). C++ users may find @ref grp_rt_cpp_lock
+ * interesting.
+ *
+ * @ingroup grp_rt
+ * @{
+ */
+
+
+/** @name Generic Semaphore Wait Flags.
+ *
+ * @remarks Exactly one of RTSEMWAIT_FLAGS_RELATIVE and
+ * RTSEMWAIT_FLAGS_ABSOLUTE must be set, unless
+ * RTSEMWAIT_FLAGS_INDEFINITE is used.
+ *
+ * Exactly one of RTSEMWAIT_FLAGS_NANOSECS and
+ * RTSEMWAIT_FLAGS_MILLISECS must be set, unless
+ * RTSEMWAIT_FLAGS_INDEFINITE is used.
+ *
+ * Exactly one of RTSEMWAIT_FLAGS_RESUME and RTSEMWAIT_FLAGS_NORESUME
+ * must be set.
+ *
+ * The interruptible vs resume stuff is ring-0 vs ring-3 semantics.
+ *
+ * @{ */
+/** The timeout is relative. */
+#define RTSEMWAIT_FLAGS_RELATIVE RT_BIT_32(0)
+/** The timeout is absolute. */
+#define RTSEMWAIT_FLAGS_ABSOLUTE RT_BIT_32(1)
+/** The timeout is specified in nanoseconds. */
+#define RTSEMWAIT_FLAGS_NANOSECS RT_BIT_32(2)
+/** The timeout is specified in milliseconds. */
+#define RTSEMWAIT_FLAGS_MILLISECS RT_BIT_32(3)
+/** Indefinite wait.
+ * The relative/absolute and nano-/millisecond flags are ignored. */
+#define RTSEMWAIT_FLAGS_INDEFINITE RT_BIT_32(4)
+/** Mask covering the time related bits. */
+#define RTSEMWAIT_FLAGS_TIME_MASK UINT32_C(0x0000001f)
+
+/** Interruptible wait. */
+#define RTSEMWAIT_FLAGS_INTERRUPTIBLE RT_BIT_32(5)
+/** No automatic resume, same as interruptible. */
+#define RTSEMWAIT_FLAGS_NORESUME RTSEMWAIT_FLAGS_INTERRUPTIBLE
+/** Uninterruptible wait. */
+#define RTSEMWAIT_FLAGS_UNINTERRUPTIBLE RT_BIT_32(6)
+/** Resume on interrupt, same as uninterruptible. */
+#define RTSEMWAIT_FLAGS_RESUME RTSEMWAIT_FLAGS_UNINTERRUPTIBLE
+
+/** Macro for validate the flags. */
+#define RTSEMWAIT_FLAGS_ARE_VALID(fFlags) \
+ ( !((fFlags) & UINT32_C(0xffffff80)) \
+ && ( ((fFlags) & RTSEMWAIT_FLAGS_INDEFINITE) \
+ ? ( (((fFlags) & UINT32_C(0x20))) ^ (((fFlags) >> 1) & UINT32_C(0x20)) ) == UINT32_C(0x20) \
+ : ( (((fFlags) & UINT32_C(0x25))) ^ (((fFlags) >> 1) & UINT32_C(0x25)) ) == UINT32_C(0x25) ))
+/** @} */
+
+
+
+/** @defgroup grp_rt_sems_event RTSemEvent - Single Release Event Semaphores
+ *
+ * Event semaphores can be used for inter-thread communication when one thread
+ * wants to notify another thread that something happened. A thread can block
+ * ("wait") on an event semaphore until it is signalled by another thread; see
+ * RTSemEventCreate, RTSemEventSignal and RTSemEventWait.
+ *
+ * @{ */
+
+/**
+ * Create an event semaphore.
+ *
+ * @returns iprt status code.
+ * @param phEventSem Where to store the handle to the newly created
+ * event semaphore.
+ */
+RTDECL(int) RTSemEventCreate(PRTSEMEVENT phEventSem);
+
+/**
+ * Create an event semaphore.
+ *
+ * @returns iprt status code.
+ * @param phEventSem Where to store the handle to the newly created
+ * event semaphore.
+ * @param fFlags Flags, any combination of the
+ * RTSEMEVENT_FLAGS_XXX \#defines.
+ * @param hClass The class (no reference consumed). Since we
+ * don't do order checks on event semaphores, the
+ * use of the class is limited to controlling the
+ * timeout threshold for deadlock detection.
+ * @param pszNameFmt Name format string for the lock validator,
+ * optional (NULL). Max length is 32 bytes.
+ * @param ... Format string arguments.
+ */
+RTDECL(int) RTSemEventCreateEx(PRTSEMEVENT phEventSem, uint32_t fFlags, RTLOCKVALCLASS hClass,
+ const char *pszNameFmt, ...) RT_IPRT_FORMAT_ATTR_MAYBE_NULL(4, 5);
+
+/** @name RTSemMutexCreateEx flags
+ * @{ */
+/** Disables lock validation. */
+#define RTSEMEVENT_FLAGS_NO_LOCK_VAL UINT32_C(0x00000001)
+/** Bootstrap hack for use with certain memory allocator locks only! */
+#define RTSEMEVENT_FLAGS_BOOTSTRAP_HACK UINT32_C(0x00000004)
+/** @} */
+
+/**
+ * Destroy an event semaphore.
+ *
+ * @returns iprt status code.
+ * @param hEventSem Handle of the event semaphore. NIL_RTSEMEVENT
+ * is quietly ignored (VINF_SUCCESS).
+ */
+RTDECL(int) RTSemEventDestroy(RTSEMEVENT hEventSem);
+
+/**
+ * Signal an event semaphore.
+ *
+ * The event semaphore will be signaled and automatically reset after exactly
+ * one thread have successfully returned from RTSemEventWait() after
+ * waiting/polling on that semaphore.
+ *
+ * @returns iprt status code.
+ * @param hEventSem The event semaphore to signal.
+ *
+ * @remarks ring-0: This works when preemption is disabled. However it is
+ * system specific whether it works in interrupt context or with
+ * interrupts disabled.
+ *
+ * ring-0/Darwin: This works when interrupts are disabled and thereby
+ * in interrupt context, except it cannot race semaphore destruction as
+ * the allocator does not work under these circumstances.
+ */
+RTDECL(int) RTSemEventSignal(RTSEMEVENT hEventSem);
+
+/**
+ * Whether RTSemEventSignal can be safely called w/o risk of preemption.
+ *
+ * Checks whether the caller can safely signal a single release semaphore
+ * without any risk of getting preempted on locks or similar while doing so.
+ * This also checks whether the context is suitable in general.
+ *
+ * @returns true if safe, false if not.
+ * @remarks Only ring-0.
+ */
+RTR0DECL(bool) RTSemEventIsSignalSafe(void);
+
+/**
+ * Wait for the event semaphore to be signaled, resume on interruption.
+ *
+ * This function will resume if the wait is interrupted by an async system event
+ * (like a unix signal) or similar.
+ *
+ * @returns iprt status code.
+ * Will not return VERR_INTERRUPTED.
+ * @param hEventSem The event semaphore to wait on.
+ * @param cMillies Number of milliseconds to wait.
+ */
+RTDECL(int) RTSemEventWait(RTSEMEVENT hEventSem, RTMSINTERVAL cMillies);
+
+/**
+ * Wait for the event semaphore to be signaled, return on interruption.
+ *
+ * This function will not resume the wait if interrupted.
+ *
+ * @returns iprt status code.
+ * @param hEventSem The event semaphore to wait on.
+ * @param cMillies Number of milliseconds to wait.
+ */
+RTDECL(int) RTSemEventWaitNoResume(RTSEMEVENT hEventSem, RTMSINTERVAL cMillies);
+
+/**
+ * Extended API for waiting on an event semaphore to be signaled.
+ *
+ * @returns IPRT status code.
+ * @param hEventSem The event semaphore to wait on.
+ * @param fFlags Combination of RTSEMWAIT_FLAGS_XXX.
+ * @param uTimeout The timeout, ignored if
+ * RTSEMWAIT_FLAGS_INDEFINITE is set in @a flags.
+ * Whether this is absolute or relative,
+ * milliseconds or nanoseconds depends on the @a
+ * fFlags value. Do not pass RT_INDEFINITE_WAIT
+ * here, use RTSEMWAIT_FLAGS_INDEFINITE instead.
+ */
+RTDECL(int) RTSemEventWaitEx(RTSEMEVENT hEventSem, uint32_t fFlags, uint64_t uTimeout);
+
+/**
+ * Debug version of RTSemEventWaitEx that tracks the location.
+ *
+ * @returns IPRT status code, see RTSemEventWaitEx.
+ * @param hEventSem The event semaphore to wait on.
+ * @param fFlags See RTSemEventWaitEx.
+ * @param uTimeout See RTSemEventWaitEx.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemEventWaitExDebug(RTSEMEVENT hEventSem, uint32_t fFlags, uint64_t uTimeout,
+ RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Gets the best timeout resolution that RTSemEventWaitEx can do.
+ *
+ * @returns The resolution in nanoseconds.
+ */
+RTDECL(uint32_t) RTSemEventGetResolution(void);
+
+/**
+ * Sets the signaller thread to one specific thread.
+ *
+ * This is only used for validating usage and deadlock detection. When used
+ * after calls to RTSemEventAddSignaller, the specified thread will be the only
+ * signalling thread.
+ *
+ * @param hEventSem The event semaphore.
+ * @param hThread The thread that will signal it. Pass
+ * NIL_RTTHREAD to indicate that there is no
+ * special signalling thread.
+ */
+RTDECL(void) RTSemEventSetSignaller(RTSEMEVENT hEventSem, RTTHREAD hThread);
+
+/**
+ * To add more signalling threads.
+ *
+ * First call RTSemEventSetSignaller then add further threads with this.
+ *
+ * @param hEventSem The event semaphore.
+ * @param hThread The thread that will signal it. NIL_RTTHREAD is
+ * not accepted.
+ */
+RTDECL(void) RTSemEventAddSignaller(RTSEMEVENT hEventSem, RTTHREAD hThread);
+
+/**
+ * To remove a signalling thread.
+ *
+ * Reverts work done by RTSemEventAddSignaller and RTSemEventSetSignaller.
+ *
+ * @param hEventSem The event semaphore.
+ * @param hThread A previously added thread.
+ */
+RTDECL(void) RTSemEventRemoveSignaller(RTSEMEVENT hEventSem, RTTHREAD hThread);
+
+/** @} */
+
+
+/** @defgroup grp_rt_sems_event_multi RTSemEventMulti - Multiple Release Event Semaphores
+ *
+ * A variant of @ref grp_rt_sems_event where all threads will be unblocked when
+ * signalling the semaphore.
+ *
+ * @{ */
+
+/**
+ * Creates a multiple release event semaphore.
+ *
+ * @returns iprt status code.
+ * @param phEventMultiSem Where to store the handle to the newly created
+ * multiple release event semaphore.
+ */
+RTDECL(int) RTSemEventMultiCreate(PRTSEMEVENTMULTI phEventMultiSem);
+
+/**
+ * Creates a multiple release event semaphore.
+ *
+ * @returns iprt status code.
+ * @param phEventMultiSem Where to store the handle to the newly created
+ * multiple release event semaphore.
+ * @param fFlags Flags, any combination of the
+ * RTSEMEVENTMULTI_FLAGS_XXX \#defines.
+ * @param hClass The class (no reference consumed). Since we
+ * don't do order checks on event semaphores, the
+ * use of the class is limited to controlling the
+ * timeout threshold for deadlock detection.
+ * @param pszNameFmt Name format string for the lock validator,
+ * optional (NULL). Max length is 32 bytes.
+ * @param ... Format string arguments.
+ */
+RTDECL(int) RTSemEventMultiCreateEx(PRTSEMEVENTMULTI phEventMultiSem, uint32_t fFlags, RTLOCKVALCLASS hClass,
+ const char *pszNameFmt, ...) RT_IPRT_FORMAT_ATTR_MAYBE_NULL(4, 5);
+
+/** @name RTSemMutexCreateEx flags
+ * @{ */
+/** Disables lock validation. */
+#define RTSEMEVENTMULTI_FLAGS_NO_LOCK_VAL UINT32_C(0x00000001)
+/** @} */
+
+/**
+ * Destroy an event multi semaphore.
+ *
+ * @returns iprt status code.
+ * @param hEventMultiSem The multiple release event semaphore. NIL is
+ * quietly ignored (VINF_SUCCESS).
+ */
+RTDECL(int) RTSemEventMultiDestroy(RTSEMEVENTMULTI hEventMultiSem);
+
+/**
+ * Signal an event multi semaphore.
+ *
+ * @returns iprt status code.
+ * @param hEventMultiSem The multiple release event semaphore.
+ *
+ * @remarks ring-0: This works when preemption is disabled. However it is
+ * system specific whether it works in interrupt context or with
+ * interrupts disabled.
+ *
+ * ring-0/Darwin: This works when interrupts are disabled and thereby
+ * in interrupt context, except it cannot race semaphore destruction as
+ * the allocator does not work under these circumstances.
+ */
+RTDECL(int) RTSemEventMultiSignal(RTSEMEVENTMULTI hEventMultiSem);
+
+/**
+ * Whether RTSemEventMultiSignal can be safely called w/o risk of preemption.
+ *
+ * Checks whether the caller can safely signal a multiple release semaphore
+ * without any risk of getting preempted on locks or similar while doing so.
+ * This also checks whether the context is suitable in general.
+ *
+ * @returns true if safe, false if not.
+ * @remarks Only ring-0.
+ */
+RTR0DECL(bool) RTSemEventMultiIsSignalSafe(void);
+
+/**
+ * Resets an event multi semaphore to non-signaled state.
+ *
+ * @returns iprt status code.
+ * @param hEventMultiSem The multiple release event semaphore.
+ */
+RTDECL(int) RTSemEventMultiReset(RTSEMEVENTMULTI hEventMultiSem);
+
+/**
+ * Wait for the event multi semaphore to be signaled, resume on interruption.
+ *
+ * This function will resume if the wait is interrupted by an async
+ * system event (like a unix signal) or similar.
+ *
+ * @returns iprt status code.
+ * Will not return VERR_INTERRUPTED.
+ * @param hEventMultiSem The multiple release event semaphore.
+ * @param cMillies Number of milliseconds to wait.
+ */
+RTDECL(int) RTSemEventMultiWait(RTSEMEVENTMULTI hEventMultiSem, RTMSINTERVAL cMillies);
+
+/**
+ * Wait for the event multi semaphore to be signaled, return on interruption.
+ *
+ * This function will not resume the wait if interrupted.
+ *
+ * @returns iprt status code.
+ * @param hEventMultiSem The multiple release event semaphore.
+ * @param cMillies Number of milliseconds to wait.
+ * @todo Rename to RTSemEventMultiWaitIntr since it is mainly for
+ * ring-0 consumption.
+ */
+RTDECL(int) RTSemEventMultiWaitNoResume(RTSEMEVENTMULTI hEventMultiSem, RTMSINTERVAL cMillies);
+
+/**
+ * Extended API for waiting on an event semaphore to be signaled.
+ *
+ * @returns IPRT status code.
+ * @param hEventMultiSem The multiple release event semaphore to wait
+ * on.
+ * @param fFlags Combination of the RTSEMWAIT_FLAGS_XXX.
+ * @param uTimeout The timeout, ignored if
+ * RTSEMWAIT_FLAGS_INDEFINITE is set in @a flags.
+ * Whether this is absolute or relative,
+ * milliseconds or nanoseconds depends on the @a
+ * fFlags value. Do not pass RT_INDEFINITE_WAIT
+ * here, use RTSEMWAIT_FLAGS_INDEFINITE instead.
+ */
+RTDECL(int) RTSemEventMultiWaitEx(RTSEMEVENTMULTI hEventMultiSem, uint32_t fFlags, uint64_t uTimeout);
+
+/**
+ * Debug version of RTSemEventMultiWaitEx that tracks the location.
+
+ * @returns IPRT status code, see RTSemEventMultiWaitEx.
+ * @param hEventMultiSem The multiple release event semaphore handle.
+ * @param fFlags See RTSemEventMultiWaitEx.
+ * @param uTimeout See RTSemEventMultiWaitEx.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemEventMultiWaitExDebug(RTSEMEVENTMULTI hEventMultiSem, uint32_t fFlags, uint64_t uTimeout,
+ RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Gets the best timeout resolution that RTSemEventMultiWaitEx can do.
+ *
+ * @returns The resolution in nanoseconds.
+ */
+RTDECL(uint32_t) RTSemEventMultiGetResolution(void);
+
+/**
+ * Sets the signaller thread to one specific thread.
+ *
+ * This is only used for validating usage and deadlock detection. When used
+ * after calls to RTSemEventAddSignaller, the specified thread will be the only
+ * signalling thread.
+ *
+ * @param hEventMultiSem The multiple release event semaphore.
+ * @param hThread The thread that will signal it. Pass
+ * NIL_RTTHREAD to indicate that there is no
+ * special signalling thread.
+ */
+RTDECL(void) RTSemEventMultiSetSignaller(RTSEMEVENTMULTI hEventMultiSem, RTTHREAD hThread);
+
+/**
+ * To add more signalling threads.
+ *
+ * First call RTSemEventSetSignaller then add further threads with this.
+ *
+ * @param hEventMultiSem The multiple release event semaphore.
+ * @param hThread The thread that will signal it. NIL_RTTHREAD is
+ * not accepted.
+ */
+RTDECL(void) RTSemEventMultiAddSignaller(RTSEMEVENTMULTI hEventMultiSem, RTTHREAD hThread);
+
+/**
+ * To remove a signalling thread.
+ *
+ * Reverts work done by RTSemEventAddSignaller and RTSemEventSetSignaller.
+ *
+ * @param hEventMultiSem The multiple release event semaphore.
+ * @param hThread A previously added thread.
+ */
+RTDECL(void) RTSemEventMultiRemoveSignaller(RTSEMEVENTMULTI hEventMultiSem, RTTHREAD hThread);
+
+/** @} */
+
+
+/** @defgroup grp_rt_sems_mutex RTSemMutex - Mutex semaphores.
+ *
+ * Mutex semaphores protect a section of code or data to which access must be
+ * exclusive. Only one thread can hold access to a critical section at one
+ * time. See RTSemMutexCreate, RTSemMutexRequest and RTSemMutexRelease.
+ *
+ * @remarks These are less efficient than "fast mutexes" and "critical
+ * sections", which IPRT implements as well; see @ref
+ * grp_rt_sems_fast_mutex and @ref grp_rt_critsect .
+ *
+ * @{ */
+
+/**
+ * Create a mutex semaphore.
+ *
+ * @returns iprt status code.
+ * @param phMutexSem Where to store the mutex semaphore handle.
+ */
+RTDECL(int) RTSemMutexCreate(PRTSEMMUTEX phMutexSem);
+
+/**
+ * Creates a read/write semaphore.
+ *
+ * @returns iprt status code.
+ * @param phMutexSem Where to store the handle to the newly created
+ * mutex semaphore.
+ * @param fFlags Flags, any combination of the
+ * RTSEMMUTEX_FLAGS_XXX \#defines.
+ * @param hClass The class (no reference consumed). If NIL, no
+ * lock order validation will be performed on this
+ * lock.
+ * @param uSubClass The sub-class. This is used to define lock
+ * order within a class. RTLOCKVAL_SUB_CLASS_NONE
+ * is the recommended value here.
+ * @param pszNameFmt Name format string for the lock validator,
+ * optional (NULL). Max length is 32 bytes.
+ * @param ... Format string arguments.
+ */
+RTDECL(int) RTSemMutexCreateEx(PRTSEMMUTEX phMutexSem, uint32_t fFlags, RTLOCKVALCLASS hClass, uint32_t uSubClass,
+ const char *pszNameFmt, ...) RT_IPRT_FORMAT_ATTR_MAYBE_NULL(5, 6);
+
+/** @name RTSemMutexCreateEx flags
+ * @{ */
+/** Disables lock validation. */
+#define RTSEMMUTEX_FLAGS_NO_LOCK_VAL UINT32_C(0x00000001)
+/** @} */
+
+
+/**
+ * Destroy a mutex semaphore.
+ *
+ * @returns iprt status code.
+ * @param hMutexSem The mutex semaphore to destroy. NIL is quietly
+ * ignored (VINF_SUCCESS).
+ */
+RTDECL(int) RTSemMutexDestroy(RTSEMMUTEX hMutexSem);
+
+/**
+ * Changes the lock validator sub-class of the mutex semaphore.
+ *
+ * It is recommended to try make sure that nobody is using this semaphore while
+ * changing the value.
+ *
+ * @returns The old sub-class. RTLOCKVAL_SUB_CLASS_INVALID is returns if the
+ * lock validator isn't compiled in or either of the parameters are
+ * invalid.
+ * @param hMutexSem The handle to the mutex semaphore.
+ * @param uSubClass The new sub-class value.
+ */
+RTDECL(uint32_t) RTSemMutexSetSubClass(RTSEMMUTEX hMutexSem, uint32_t uSubClass);
+
+/**
+ * Request ownership of a mutex semaphore, resume on interruption.
+ *
+ * This function will resume if the wait is interrupted by an async
+ * system event (like a unix signal) or similar.
+ *
+ * The same thread may request a mutex semaphore multiple times,
+ * a nested counter is kept to make sure it's released on the right
+ * RTSemMutexRelease() call.
+ *
+ * @returns iprt status code.
+ * Will not return VERR_INTERRUPTED.
+ * @param hMutexSem The mutex semaphore to request ownership over.
+ * @param cMillies The number of milliseconds to wait.
+ */
+RTDECL(int) RTSemMutexRequest(RTSEMMUTEX hMutexSem, RTMSINTERVAL cMillies);
+
+/**
+ * Request ownership of a mutex semaphore, return on interruption.
+ *
+ * This function will not resume the wait if interrupted.
+ *
+ * The same thread may request a mutex semaphore multiple times,
+ * a nested counter is kept to make sure it's released on the right
+ * RTSemMutexRelease() call.
+ *
+ * @returns iprt status code.
+ * @param hMutexSem The mutex semaphore to request ownership over.
+ * @param cMillies The number of milliseconds to wait.
+ */
+RTDECL(int) RTSemMutexRequestNoResume(RTSEMMUTEX hMutexSem, RTMSINTERVAL cMillies);
+
+/**
+ * Debug version of RTSemMutexRequest that tracks the location.
+ *
+ * @returns iprt status code.
+ * Will not return VERR_INTERRUPTED.
+ * @param hMutexSem The mutex semaphore to request ownership over.
+ * @param cMillies The number of milliseconds to wait.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemMutexRequestDebug(RTSEMMUTEX hMutexSem, RTMSINTERVAL cMillies, RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Debug version of RTSemMutexRequestNoResume that tracks the location.
+ *
+ * @returns iprt status code.
+ * @param hMutexSem The mutex semaphore to request ownership over.
+ * @param cMillies The number of milliseconds to wait.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemMutexRequestNoResumeDebug(RTSEMMUTEX hMutexSem, RTMSINTERVAL cMillies, RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Request ownership of a mutex semaphore, extended edition.
+ *
+ * The same thread may request a mutex semaphore multiple times,
+ * a nested counter is kept to make sure it's released on the right
+ * RTSemMutexRelease() call.
+ *
+ * @returns iprt status code.
+ * @param hMutexSem The mutex semaphore to request ownership over.
+ * @param fFlags Combination of the RTSEMWAIT_FLAGS_XXX.
+ * @param uTimeout The timeout, ignored if
+ * RTSEMWAIT_FLAGS_INDEFINITE is set in @a flags.
+ * Whether this is absolute or relative,
+ * milliseconds or nanoseconds depends on the @a
+ * fFlags value. Do not pass RT_INDEFINITE_WAIT
+ * here, use RTSEMWAIT_FLAGS_INDEFINITE instead.
+ */
+RTDECL(int) RTSemMutexRequestEx(RTSEMMUTEX hMutexSem, uint32_t fFlags, uint64_t uTimeout);
+
+/**
+ * Debug version of RTSemMutexRequestEx that tracks the location.
+ *
+ * @returns iprt status code.
+ * @param hMutexSem The mutex semaphore to request ownership over.
+ * @param fFlags See RTSemMutexRequestEx.
+ * @param uTimeout See RTSemMutexRequestEx.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemMutexRequestExDebug(RTSEMMUTEX hMutexSem, uint32_t fFlags, uint64_t uTimeout,
+ RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Release the ownership of a mutex semaphore.
+ *
+ * @returns iprt status code.
+ * @param hMutexSem The mutex to release the ownership of. It goes
+ * without saying the the calling thread must own
+ * it.
+ */
+RTDECL(int) RTSemMutexRelease(RTSEMMUTEX hMutexSem);
+
+/**
+ * Checks if the mutex semaphore is owned or not.
+ *
+ * @returns true if owned, false if not.
+ * @param hMutexSem The mutex semaphore.
+ */
+RTDECL(bool) RTSemMutexIsOwned(RTSEMMUTEX hMutexSem);
+
+/* Strict build: Remap the two request calls to the debug versions. */
+#if defined(RT_STRICT) && !defined(RTSEMMUTEX_WITHOUT_REMAPPING) && !defined(RT_WITH_MANGLING)
+# ifdef IPRT_INCLUDED_asm_h
+# define RTSemMutexRequest(hMutexSem, cMillies) RTSemMutexRequestDebug((hMutexSem), (cMillies), (uintptr_t)ASMReturnAddress(), RT_SRC_POS)
+# define RTSemMutexRequestNoResume(hMutexSem, cMillies) RTSemMutexRequestNoResumeDebug((hMutexSem), (cMillies), (uintptr_t)ASMReturnAddress(), RT_SRC_POS)
+# define RTSemMutexRequestEx(hMutexSem, fFlags, uTimeout) RTSemMutexRequestExDebug((hMutexSem), (fFlags), (uTimeout), (uintptr_t)ASMReturnAddress(), RT_SRC_POS)
+# else
+# define RTSemMutexRequest(hMutexSem, cMillies) RTSemMutexRequestDebug((hMutexSem), (cMillies), 0, RT_SRC_POS)
+# define RTSemMutexRequestNoResume(hMutexSem, cMillies) RTSemMutexRequestNoResumeDebug((hMutexSem), (cMillies), 0, RT_SRC_POS)
+# define RTSemMutexRequestEx(hMutexSem, fFlags, uTimeout) RTSemMutexRequestExDebug((hMutexSem), (fFlags), (uTimeout), 0, RT_SRC_POS)
+# endif
+#endif
+
+/* Strict lock order: Automatically classify locks by init location. */
+#if defined(RT_LOCK_STRICT_ORDER) && defined(IN_RING3) && !defined(RTSEMMUTEX_WITHOUT_REMAPPING) && !defined(RT_WITH_MANGLING)
+# define RTSemMutexCreate(phMutexSem) \
+ RTSemMutexCreateEx((phMutexSem), 0 /*fFlags*/, \
+ RTLockValidatorClassForSrcPos(RT_SRC_POS, NULL), \
+ RTLOCKVAL_SUB_CLASS_NONE, NULL)
+#endif
+
+/** @} */
+
+
+/** @defgroup grp_rt_sems_fast_mutex RTSemFastMutex - Fast Mutex Semaphores
+ *
+ * Fast mutexes work like regular mutexes in that they allow only a single
+ * thread access to a critical piece of code or data. As opposed to mutexes,
+ * they require no syscall if the fast mutex is not held (like critical
+ * sections). Unlike critical sections however, they are *not* recursive.
+ *
+ * @remarks The fast mutexes has sideeffects on IRQL on Windows hosts. So use
+ * with care and test on windows with the driver verifier enabled.
+ *
+ * @{ */
+
+/**
+ * Create a fast mutex semaphore.
+ *
+ * @returns iprt status code.
+ * @param phFastMtx Where to store the handle to the newly created
+ * fast mutex semaphore.
+ *
+ * @remarks Fast mutex semaphores are not recursive.
+ */
+RTDECL(int) RTSemFastMutexCreate(PRTSEMFASTMUTEX phFastMtx);
+
+/**
+ * Destroy a fast mutex semaphore.
+ *
+ * @returns iprt status code.
+ * @param hFastMtx Handle to the fast mutex semaphore. NIL is
+ * quietly ignored (VINF_SUCCESS).
+ */
+RTDECL(int) RTSemFastMutexDestroy(RTSEMFASTMUTEX hFastMtx);
+
+/**
+ * Request ownership of a fast mutex semaphore.
+ *
+ * @returns iprt status code.
+ * @param hFastMtx Handle to the fast mutex semaphore.
+ */
+RTDECL(int) RTSemFastMutexRequest(RTSEMFASTMUTEX hFastMtx);
+
+/**
+ * Release the ownership of a fast mutex semaphore.
+ *
+ * @returns iprt status code.
+ * @param hFastMtx Handle to the fast mutex semaphore. It goes
+ * without saying the the calling thread must own
+ * it.
+ */
+RTDECL(int) RTSemFastMutexRelease(RTSEMFASTMUTEX hFastMtx);
+
+/** @} */
+
+
+/** @defgroup grp_rt_sems_spin_mutex RTSemSpinMutex - Spinning Mutex Semaphores
+ *
+ * A very adaptive variant of mutex semaphore that is tailored for the ring-0
+ * logger.
+ *
+ * @{ */
+
+/**
+ * Creates a spinning mutex semaphore.
+ *
+ * @returns iprt status code.
+ * @retval VERR_INVALID_PARAMETER on invalid flags.
+ * @retval VERR_NO_MEMORY if out of memory for the semaphore structure and
+ * handle.
+ *
+ * @param phSpinMtx Where to return the handle to the create semaphore.
+ * @param fFlags Flags, see RTSEMSPINMUTEX_FLAGS_XXX.
+ */
+RTDECL(int) RTSemSpinMutexCreate(PRTSEMSPINMUTEX phSpinMtx, uint32_t fFlags);
+
+/** @name RTSemSpinMutexCreate flags.
+ * @{ */
+/** Always take the semaphore in a IRQ safe way.
+ * (In plain words: always disable interrupts.) */
+#define RTSEMSPINMUTEX_FLAGS_IRQ_SAFE RT_BIT_32(0)
+/** Mask of valid flags. */
+#define RTSEMSPINMUTEX_FLAGS_VALID_MASK UINT32_C(0x00000001)
+/** @} */
+
+/**
+ * Destroys a spinning mutex semaphore.
+ *
+ * @returns iprt status code.
+ * @retval VERR_INVALID_HANDLE (or crash) if the handle is invalid. (NIL will
+ * not cause this status.)
+ *
+ * @param hSpinMtx The semaphore handle. NIL_RTSEMSPINMUTEX is ignored
+ * quietly (VINF_SUCCESS).
+ */
+RTDECL(int) RTSemSpinMutexDestroy(RTSEMSPINMUTEX hSpinMtx);
+
+/**
+ * Request the spinning mutex semaphore.
+ *
+ * This may block if the context we're called in allows this. If not it will
+ * spin. If called in an interrupt context, we will only spin if the current
+ * owner isn't interrupted. Also, on some systems it is not always possible to
+ * wake up blocking threads in all contexts, so, which will either be indicated
+ * by returning VERR_SEM_BAD_CONTEXT or by temporarily switching the semaphore
+ * into pure spinlock state.
+ *
+ * Preemption will be disabled upon return. IRQs may also be disabled.
+ *
+ * @returns iprt status code.
+ * @retval VERR_SEM_BAD_CONTEXT if the context it's called in isn't suitable
+ * for releasing it if someone is sleeping on it.
+ * @retval VERR_SEM_DESTROYED if destroyed.
+ * @retval VERR_SEM_NESTED if held by the caller. Asserted.
+ * @retval VERR_INVALID_HANDLE if the handle is invalid. Asserted
+ *
+ * @param hSpinMtx The semaphore handle.
+ */
+RTDECL(int) RTSemSpinMutexRequest(RTSEMSPINMUTEX hSpinMtx);
+
+/**
+ * Like RTSemSpinMutexRequest but it won't block or spin if the semaphore is
+ * held by someone else.
+ *
+ * @returns iprt status code.
+ * @retval VERR_SEM_BUSY if held by someone else.
+ * @retval VERR_SEM_DESTROYED if destroyed.
+ * @retval VERR_SEM_NESTED if held by the caller. Asserted.
+ * @retval VERR_INVALID_HANDLE if the handle is invalid. Asserted
+ *
+ * @param hSpinMtx The semaphore handle.
+ */
+RTDECL(int) RTSemSpinMutexTryRequest(RTSEMSPINMUTEX hSpinMtx);
+
+/**
+ * Releases the semaphore previously acquired by RTSemSpinMutexRequest or
+ * RTSemSpinMutexTryRequest.
+ *
+ * @returns iprt status code.
+ * @retval VERR_SEM_DESTROYED if destroyed.
+ * @retval VERR_NOT_OWNER if not owner. Asserted.
+ * @retval VERR_INVALID_HANDLE if the handle is invalid. Asserted.
+ *
+ * @param hSpinMtx The semaphore handle.
+ */
+RTDECL(int) RTSemSpinMutexRelease(RTSEMSPINMUTEX hSpinMtx);
+
+/** @} */
+
+
+/** @defgroup grp_rt_sem_rw RTSemRW - Read / Write Semaphores
+ *
+ * Read/write semaphores are a fancier version of mutexes in that they grant
+ * read access to the protected data to several threads at the same time but
+ * allow only one writer at a time. This can make code scale better at the
+ * expense of slightly more overhead in mutex management.
+ *
+ * @{ */
+
+/**
+ * Creates a read/write semaphore.
+ *
+ * @returns iprt status code.
+ * @param phRWSem Where to store the handle to the newly created
+ * RW semaphore.
+ */
+RTDECL(int) RTSemRWCreate(PRTSEMRW phRWSem);
+
+/**
+ * Creates a read/write semaphore.
+ *
+ * @returns iprt status code.
+ * @param phRWSem Where to store the handle to the newly created
+ * RW semaphore.
+ * @param fFlags Flags, any combination of the RTSEMRW_FLAGS_XXX
+ * \#defines.
+ * @param hClass The class (no reference consumed). If NIL, no
+ * lock order validation will be performed on this
+ * lock.
+ * @param uSubClass The sub-class. This is used to define lock
+ * order within a class. RTLOCKVAL_SUB_CLASS_NONE
+ * is the recommended value here.
+ * @param pszNameFmt Name format string for the lock validator,
+ * optional (NULL). Max length is 32 bytes.
+ * @param ... Format string arguments.
+ */
+RTDECL(int) RTSemRWCreateEx(PRTSEMRW phRWSem, uint32_t fFlags, RTLOCKVALCLASS hClass, uint32_t uSubClass,
+ const char *pszNameFmt, ...) RT_IPRT_FORMAT_ATTR_MAYBE_NULL(5, 6);
+
+/** @name RTSemRWCreateEx flags
+ * @{ */
+/** Disables lock validation. */
+#define RTSEMRW_FLAGS_NO_LOCK_VAL UINT32_C(0x00000001)
+/** @} */
+
+/**
+ * Destroys a read/write semaphore.
+ *
+ * @returns iprt status code.
+ * @param hRWSem Handle to the read/write semaphore. NIL is
+ * quietly ignored (VINF_SUCCESS).
+ */
+RTDECL(int) RTSemRWDestroy(RTSEMRW hRWSem);
+
+/**
+ * Changes the lock validator sub-class of the read/write semaphore.
+ *
+ * It is recommended to try make sure that nobody is using this semaphore while
+ * changing the value.
+ *
+ * @returns The old sub-class. RTLOCKVAL_SUB_CLASS_INVALID is returns if the
+ * lock validator isn't compiled in or either of the parameters are
+ * invalid.
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param uSubClass The new sub-class value.
+ */
+RTDECL(uint32_t) RTSemRWSetSubClass(RTSEMRW hRWSem, uint32_t uSubClass);
+
+/**
+ * Request read access to a read/write semaphore, resume on interruption
+ *
+ * @returns iprt status code.
+ * @retval VINF_SUCCESS on success.
+ * @retval VERR_INTERRUPT if the wait was interrupted.
+ * @retval VERR_INVALID_HANDLE if hRWSem is invalid.
+ *
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param cMillies The number of milliseconds to wait.
+ */
+RTDECL(int) RTSemRWRequestRead(RTSEMRW hRWSem, RTMSINTERVAL cMillies);
+
+/**
+ * Request read access to a read/write semaphore, return on interruption
+ *
+ * @returns iprt status code.
+ * @retval VINF_SUCCESS on success.
+ * @retval VERR_INTERRUPT if the wait was interrupted.
+ * @retval VERR_INVALID_HANDLE if hRWSem is invalid.
+ *
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param cMillies The number of milliseconds to wait.
+ */
+RTDECL(int) RTSemRWRequestReadNoResume(RTSEMRW hRWSem, RTMSINTERVAL cMillies);
+
+/**
+ * Debug version of RTSemRWRequestRead that tracks the location.
+ *
+ * @returns iprt status code.
+ * @retval VINF_SUCCESS on success.
+ * @retval VERR_INTERRUPT if the wait was interrupted.
+ * @retval VERR_INVALID_HANDLE if hRWSem is invalid.
+ *
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param cMillies The number of milliseconds to wait.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemRWRequestReadDebug(RTSEMRW hRWSem, RTMSINTERVAL cMillies, RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Debug version of RTSemRWRequestWriteNoResume that tracks the location.
+ *
+ * @returns iprt status code.
+ * @retval VINF_SUCCESS on success.
+ * @retval VERR_INTERRUPT if the wait was interrupted.
+ * @retval VERR_INVALID_HANDLE if hRWSem is invalid.
+ *
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param cMillies The number of milliseconds to wait.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemRWRequestReadNoResumeDebug(RTSEMRW hRWSem, RTMSINTERVAL cMillies, RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Request read access to a read/write semaphore, extended edition.
+ *
+ * @returns iprt status code.
+ * @retval VINF_SUCCESS on success.
+ * @retval VERR_INTERRUPT if the wait was interrupted.
+ * @retval VERR_TIMEOUT if the wait timed out.
+ * @retval VERR_INVALID_HANDLE if hRWSem is invalid.
+ *
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param fFlags Combination of the RTSEMWAIT_FLAGS_XXX.
+ * @param uTimeout The timeout, ignored if
+ * RTSEMWAIT_FLAGS_INDEFINITE is set in @a flags.
+ * Whether this is absolute or relative,
+ * milliseconds or nanoseconds depends on the @a
+ * fFlags value. Do not pass RT_INDEFINITE_WAIT
+ * here, use RTSEMWAIT_FLAGS_INDEFINITE instead.
+ */
+RTDECL(int) RTSemRWRequestReadEx(RTSEMRW hRWSem, uint32_t fFlags, uint64_t uTimeout);
+
+
+/**
+ * Debug version of RTSemRWRequestReadEx that tracks the location.
+ *
+ * @returns iprt status code.
+ * @retval VINF_SUCCESS on success.
+ * @retval VERR_INTERRUPT if the wait was interrupted.
+ * @retval VERR_TIMEOUT if the wait timed out.
+ * @retval VERR_INVALID_HANDLE if hRWSem is invalid.
+ *
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param fFlags See RTSemRWRequestReadEx.
+ * @param uTimeout See RTSemRWRequestReadEx.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemRWRequestReadExDebug(RTSEMRW hRWSem, uint32_t fFlags, uint64_t uTimeout,
+ RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Release read access to a read/write semaphore.
+ *
+ * @returns iprt status code.
+ * @param hRWSem Handle to the read/write semaphore. It goes
+ * without saying that caller must own read
+ * privileges to the semaphore.
+ */
+RTDECL(int) RTSemRWReleaseRead(RTSEMRW hRWSem);
+
+/**
+ * Request write access to a read/write semaphore, resume on interruption.
+ *
+ * @returns iprt status code.
+ * @retval VINF_SUCCESS on success.
+ * @retval VERR_DEADLOCK if the caller owned the read lock.
+ * @retval VERR_INVALID_HANDLE if hRWSem is invalid.
+ *
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param cMillies The number of milliseconds to wait.
+ */
+RTDECL(int) RTSemRWRequestWrite(RTSEMRW hRWSem, RTMSINTERVAL cMillies);
+
+/**
+ * Request write access to a read/write semaphore, return on interruption.
+ *
+ * @returns iprt status code.
+ * @retval VINF_SUCCESS on success.
+ * @retval VERR_INTERRUPT if the wait was interrupted.
+ * @retval VERR_DEADLOCK if the caller owned the read lock.
+ * @retval VERR_INVALID_HANDLE if hRWSem is invalid.
+ *
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param cMillies The number of milliseconds to wait.
+ */
+RTDECL(int) RTSemRWRequestWriteNoResume(RTSEMRW hRWSem, RTMSINTERVAL cMillies);
+
+/**
+ * Debug version of RTSemRWRequestWrite that tracks the location.
+ *
+ * @returns IPRT status code, see RTSemRWRequestWrite.
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param cMillies The number of milliseconds to wait.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemRWRequestWriteDebug(RTSEMRW hRWSem, RTMSINTERVAL cMillies, RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Debug version of RTSemRWRequestWriteNoResume that tracks the location.
+ *
+ * @returns IPRT status code, see RTSemRWRequestWriteNoResume.
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param cMillies The number of milliseconds to wait.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemRWRequestWriteNoResumeDebug(RTSEMRW hRWSem, RTMSINTERVAL cMillies, RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Request write access to a read/write semaphore, extended edition.
+ *
+ * @returns iprt status code.
+ * @retval VINF_SUCCESS on success.
+ * @retval VERR_INTERRUPTED if the wait was interrupted.
+ * @retval VERR_TIMEOUT if the wait timed out.
+ * @retval VERR_DEADLOCK if the caller owned the read lock. Do not depend on
+ * this as it is implementation specific.
+ * @retval VERR_INVALID_HANDLE if hRWSem is invalid.
+ *
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param fFlags Combination of the RTSEMWAIT_FLAGS_XXX.
+ * @param uTimeout The timeout, ignored if
+ * RTSEMWAIT_FLAGS_INDEFINITE is set in @a flags.
+ * Whether this is absolute or relative,
+ * milliseconds or nanoseconds depends on the @a
+ * fFlags value. Do not pass RT_INDEFINITE_WAIT
+ * here, use RTSEMWAIT_FLAGS_INDEFINITE instead.
+ */
+RTDECL(int) RTSemRWRequestWriteEx(RTSEMRW hRWSem, uint32_t fFlags, uint64_t uTimeout);
+
+/**
+ * Debug version of RTSemRWRequestWriteEx that tracks the location.
+ *
+ * @returns IPRT status code, see RTSemRWRequestWriteEx.
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param fFlags See RTSemRWRequestWriteEx.
+ * @param uTimeout See RTSemRWRequestWriteEx.
+ * @param uId Some kind of locking location ID. Typically a
+ * return address up the stack. Optional (0).
+ * @param SRC_POS The source position where call is being made
+ * from. Use RT_SRC_POS when possible. Optional.
+ */
+RTDECL(int) RTSemRWRequestWriteExDebug(RTSEMRW hRWSem, uint32_t fFlags, uint64_t uTimeout,
+ RTHCUINTPTR uId, RT_SRC_POS_DECL);
+
+/**
+ * Release write access to a read/write semaphore.
+ *
+ * @returns iprt status code.
+ * @param hRWSem Handle to the read/write semaphore. Goes
+ * without saying that caller must have write
+ * access to the semaphore.
+ */
+RTDECL(int) RTSemRWReleaseWrite(RTSEMRW hRWSem);
+
+/**
+ * Checks if the caller is the exclusive semaphore owner.
+ *
+ * @returns true / false accoringly.
+ * @param hRWSem Handle to the read/write semaphore.
+ */
+RTDECL(bool) RTSemRWIsWriteOwner(RTSEMRW hRWSem);
+
+/**
+ * Checks if the caller is one of the read owners of the semaphore.
+ *
+ * @note !CAUTION! This API doesn't work reliably if lock validation isn't
+ * enabled. Meaning, the answer is not trustworhty unless
+ * RT_LOCK_STRICT or RTSEMRW_STRICT was defined at build time. Also,
+ * make sure you do not use RTSEMRW_FLAGS_NO_LOCK_VAL when creating
+ * the semaphore. And finally, if you used a locking class, don't
+ * disable deadlock detection by setting cMsMinDeadlock to
+ * RT_INDEFINITE_WAIT.
+ *
+ * In short, only use this for assertions.
+ *
+ * @returns true if reader, false if not.
+ * @param hRWSem Handle to the read/write semaphore.
+ * @param fWannaHear What you'd like to hear when lock validation is
+ * not available. (For avoiding asserting all over
+ * the place.)
+ */
+RTDECL(bool) RTSemRWIsReadOwner(RTSEMRW hRWSem, bool fWannaHear);
+
+/**
+ * Gets the write recursion count.
+ *
+ * @returns The write recursion count (0 if bad semaphore handle).
+ * @param hRWSem Handle to the read/write semaphore.
+ */
+RTDECL(uint32_t) RTSemRWGetWriteRecursion(RTSEMRW hRWSem);
+
+/**
+ * Gets the read recursion count of the current writer.
+ *
+ * @returns The read recursion count (0 if bad semaphore handle).
+ * @param hRWSem Handle to the read/write semaphore.
+ */
+RTDECL(uint32_t) RTSemRWGetWriterReadRecursion(RTSEMRW hRWSem);
+
+/**
+ * Gets the current number of reads.
+ *
+ * This includes all read recursions, so it might be higher than the number of
+ * read owners. It does not include reads done by the current writer.
+ *
+ * @returns The read count (0 if bad semaphore handle).
+ * @param hRWSem Handle to the read/write semaphore.
+ */
+RTDECL(uint32_t) RTSemRWGetReadCount(RTSEMRW hRWSem);
+
+/* Strict build: Remap the four request calls to the debug versions. */
+#if defined(RT_STRICT) && !defined(RTSEMRW_WITHOUT_REMAPPING) && !defined(RT_WITH_MANGLING)
+# ifdef IPRT_INCLUDED_asm_h
+# define RTSemRWRequestRead(hRWSem, cMillies) RTSemRWRequestReadDebug((hRWSem), (cMillies), (uintptr_t)ASMReturnAddress(), RT_SRC_POS)
+# define RTSemRWRequestReadNoResume(hRWSem, cMillies) RTSemRWRequestReadNoResumeDebug((hRWSem), (cMillies), (uintptr_t)ASMReturnAddress(), RT_SRC_POS)
+# define RTSemRWRequestWrite(hRWSem, cMillies) RTSemRWRequestWriteDebug((hRWSem), (cMillies), (uintptr_t)ASMReturnAddress(), RT_SRC_POS)
+# define RTSemRWRequestWriteNoResume(hRWSem, cMillies) RTSemRWRequestWriteNoResumeDebug((hRWSem), (cMillies), (uintptr_t)ASMReturnAddress(), RT_SRC_POS)
+# define RTSemRWRequestWriteEx(hRWSem, fFlags, uTimeout) RTSemRWRequestWriteExDebug((hRWSem), (fFlags), (uTimeout), (uintptr_t)ASMReturnAddress(), RT_SRC_POS)
+# else
+# define RTSemRWRequestRead(hRWSem, cMillies) RTSemRWRequestReadDebug((hRWSem), (cMillies), 0, RT_SRC_POS)
+# define RTSemRWRequestReadNoResume(hRWSem, cMillies) RTSemRWRequestReadNoResumeDebug((hRWSem), (cMillies), 0, RT_SRC_POS)
+# define RTSemRWRequestWrite(hRWSem, cMillies) RTSemRWRequestWriteDebug((hRWSem), (cMillies), 0, RT_SRC_POS)
+# define RTSemRWRequestWriteNoResume(hRWSem, cMillies) RTSemRWRequestWriteNoResumeDebug((hRWSem), (cMillies), 0, RT_SRC_POS)
+# define RTSemRWRequestWriteEx(hRWSem, fFlags, uTimeout) RTSemRWRequestWriteExDebug((hRWSem), (fFlags), (uTimeout), 0, RT_SRC_POS)
+# endif
+#endif
+
+/* Strict lock order: Automatically classify locks by init location. */
+#if defined(RT_LOCK_STRICT_ORDER) && defined(IN_RING3) && !defined(RTSEMRW_WITHOUT_REMAPPING) && !defined(RT_WITH_MANGLING)
+# define RTSemRWCreate(phSemRW) \
+ RTSemRWCreateEx((phSemRW), 0 /*fFlags*/, \
+ RTLockValidatorClassForSrcPos(RT_SRC_POS, NULL), \
+ RTLOCKVAL_SUB_CLASS_NONE, NULL)
+#endif
+
+/** @} */
+
+
+/** @defgroup grp_rt_sems_pingpong RTSemPingPong - Ping-Pong Construct
+ *
+ * Serialization of a two way communication.
+ *
+ * @{ */
+
+/**
+ * Ping-pong speaker
+ */
+typedef enum RTPINGPONGSPEAKER
+{
+ /** Not initialized. */
+ RTPINGPONGSPEAKER_UNINITIALIZE = 0,
+ /** Ping is speaking, Pong is waiting. */
+ RTPINGPONGSPEAKER_PING,
+ /** Pong is signaled, Ping is waiting. */
+ RTPINGPONGSPEAKER_PONG_SIGNALED,
+ /** Pong is speaking, Ping is waiting. */
+ RTPINGPONGSPEAKER_PONG,
+ /** Ping is signaled, Pong is waiting. */
+ RTPINGPONGSPEAKER_PING_SIGNALED,
+ /** Hack to ensure that it's at least 32-bits wide. */
+ RTPINGPONGSPEAKER_HACK = 0x7fffffff
+} RTPINGPONGSPEAKER;
+
+/**
+ * Ping-Pong construct.
+ *
+ * Two threads, one saying Ping and the other saying Pong. The construct
+ * makes sure they don't speak out of turn and that they can wait and poll
+ * on the conversation.
+ */
+typedef struct RTPINGPONG
+{
+ /** The semaphore the Ping thread waits on. */
+ RTSEMEVENT Ping;
+ /** The semaphore the Pong thread waits on. */
+ RTSEMEVENT Pong;
+ /** The current speaker. */
+ volatile RTPINGPONGSPEAKER enmSpeaker;
+#if HC_ARCH_BITS == 64
+ /** Padding the structure to become a multiple of sizeof(RTHCPTR). */
+ uint32_t u32Padding;
+#endif
+} RTPINGPONG;
+/** Pointer to Ping-Pong construct. */
+typedef RTPINGPONG *PRTPINGPONG;
+
+/**
+ * Init a Ping-Pong construct.
+ *
+ * @returns iprt status code.
+ * @param pPP Pointer to the ping-pong structure which needs initialization.
+ */
+RTDECL(int) RTSemPingPongInit(PRTPINGPONG pPP);
+
+/**
+ * Deletes a Ping-Pong construct.
+ *
+ * @returns iprt status code.
+ * @param pPP Pointer to the ping-pong structure which is to be destroyed.
+ * (I.e. put into uninitialized state.)
+ */
+RTDECL(int) RTSemPingPongDelete(PRTPINGPONG pPP);
+
+/**
+ * Signals the pong thread in a ping-pong construct. (I.e. sends ping.)
+ * This is called by the ping thread.
+ *
+ * @returns iprt status code.
+ * @param pPP Pointer to the ping-pong structure to ping.
+ */
+RTDECL(int) RTSemPing(PRTPINGPONG pPP);
+
+/**
+ * Signals the ping thread in a ping-pong construct. (I.e. sends pong.)
+ * This is called by the pong thread.
+ *
+ * @returns iprt status code.
+ * @param pPP Pointer to the ping-pong structure to pong.
+ */
+RTDECL(int) RTSemPong(PRTPINGPONG pPP);
+
+/**
+ * Wait function for the ping thread.
+ *
+ * @returns iprt status code.
+ * Will not return VERR_INTERRUPTED.
+ * @param pPP Pointer to the ping-pong structure to wait on.
+ * @param cMillies Number of milliseconds to wait.
+ */
+RTDECL(int) RTSemPingWait(PRTPINGPONG pPP, RTMSINTERVAL cMillies);
+
+/**
+ * Wait function for the pong thread.
+ *
+ * @returns iprt status code.
+ * Will not return VERR_INTERRUPTED.
+ * @param pPP Pointer to the ping-pong structure to wait on.
+ * @param cMillies Number of milliseconds to wait.
+ */
+RTDECL(int) RTSemPongWait(PRTPINGPONG pPP, RTMSINTERVAL cMillies);
+
+
+/**
+ * Checks if the pong thread is speaking.
+ *
+ * @returns true / false.
+ * @param pPP Pointer to the ping-pong structure.
+ * @remark This is NOT the same as !RTSemPongIsSpeaker().
+ */
+DECLINLINE(bool) RTSemPingIsSpeaker(PRTPINGPONG pPP)
+{
+ RTPINGPONGSPEAKER enmSpeaker = pPP->enmSpeaker;
+ return enmSpeaker == RTPINGPONGSPEAKER_PING;
+}
+
+
+/**
+ * Checks if the pong thread is speaking.
+ *
+ * @returns true / false.
+ * @param pPP Pointer to the ping-pong structure.
+ * @remark This is NOT the same as !RTSemPingIsSpeaker().
+ */
+DECLINLINE(bool) RTSemPongIsSpeaker(PRTPINGPONG pPP)
+{
+ RTPINGPONGSPEAKER enmSpeaker = pPP->enmSpeaker;
+ return enmSpeaker == RTPINGPONGSPEAKER_PONG;
+}
+
+
+/**
+ * Checks whether the ping thread should wait.
+ *
+ * @returns true / false.
+ * @param pPP Pointer to the ping-pong structure.
+ * @remark This is NOT the same as !RTSemPongShouldWait().
+ */
+DECLINLINE(bool) RTSemPingShouldWait(PRTPINGPONG pPP)
+{
+ RTPINGPONGSPEAKER enmSpeaker = pPP->enmSpeaker;
+ return enmSpeaker == RTPINGPONGSPEAKER_PONG
+ || enmSpeaker == RTPINGPONGSPEAKER_PONG_SIGNALED
+ || enmSpeaker == RTPINGPONGSPEAKER_PING_SIGNALED;
+}
+
+
+/**
+ * Checks whether the pong thread should wait.
+ *
+ * @returns true / false.
+ * @param pPP Pointer to the ping-pong structure.
+ * @remark This is NOT the same as !RTSemPingShouldWait().
+ */
+DECLINLINE(bool) RTSemPongShouldWait(PRTPINGPONG pPP)
+{
+ RTPINGPONGSPEAKER enmSpeaker = pPP->enmSpeaker;
+ return enmSpeaker == RTPINGPONGSPEAKER_PING
+ || enmSpeaker == RTPINGPONGSPEAKER_PING_SIGNALED
+ || enmSpeaker == RTPINGPONGSPEAKER_PONG_SIGNALED;
+}
+
+/** @} */
+
+
+/** @defgroup grp_rt_sems_xroads RTSemXRoads - Crossroads
+ *
+ * The crossroads semaphore is intended to prevent two classes of incompatible
+ * events from occurring simultaneously, like south/north bound traffic and
+ * west/east bound traffic at a 4-way junction.
+ *
+ * @remarks In order to simplify the implementation, the current flow is always
+ * given priority. So, it won't work at all well when busy!
+ *
+ * @remarks "XRoads" is used as a name because it is briefer than "crossroads"
+ * and it slightly stresses that is a 4 way crossing to the users of
+ * American English.
+ * @{
+ */
+
+/**
+ * Creates a crossroads semaphore.
+ *
+ * @returns IPRT status code.
+ *
+ * @param phXRoads Where to return the handle to the newly created
+ * crossroads semaphore.
+ */
+RTDECL(int) RTSemXRoadsCreate(PRTSEMXROADS phXRoads);
+
+/**
+ * Destroys a crossroads semaphore.
+ *
+ * @returns IPRT status code.
+ *
+ * @param hXRoads Handle to the crossroads semaphore that is to be
+ * destroyed. NIL_RTSEMXROADS is quitetly ignored
+ * (VINF_SUCCESS).
+ */
+RTDECL(int) RTSemXRoadsDestroy(RTSEMXROADS hXRoads);
+
+/**
+ * Enter the crossroads from the south or north.
+ *
+ * (Coupled with RTSemXRoadsNSLeave.)
+ *
+ * @returns IPRT status code.
+ * @param hXRoads Handle to the crossroads semaphore.
+ */
+RTDECL(int) RTSemXRoadsNSEnter(RTSEMXROADS hXRoads);
+
+/**
+ * Leave the crossroads to the north or south.
+ *
+ * (Coupled with RTSemXRoadsNSEnter.)
+ *
+ * @returns IPRT status code.
+ * @param hXRoads Handle to the crossroads semaphore.
+ */
+RTDECL(int) RTSemXRoadsNSLeave(RTSEMXROADS hXRoads);
+
+/**
+ * Leave the crossroads from the east or west.
+ *
+ * (Coupled with RTSemXRoadsEWLeave.)
+ *
+ * @returns IPRT status code.
+ * @param hXRoads Handle to the crossroads semaphore.
+ */
+RTDECL(int) RTSemXRoadsEWEnter(RTSEMXROADS hXRoads);
+
+/**
+ * Leave the crossroads to the west or east.
+ *
+ * (Coupled with RTSemXRoadsEWEnter.)
+ *
+ * @returns IPRT status code.
+ * @param hXRoads Handle to the crossroads semaphore.
+ */
+RTDECL(int) RTSemXRoadsEWLeave(RTSEMXROADS hXRoads);
+
+/** @} */
+
+/** @} */
+
+RT_C_DECLS_END
+
+#endif /* !IPRT_INCLUDED_semaphore_h */
+