xref: /reactos/sdk/lib/rtl/critical.c (revision 56417bfb)

/*
 * COPYRIGHT:       See COPYING in the top level directory
 * PROJECT:         ReactOS system libraries
 * FILE:            lib/rtl/critical.c
 * PURPOSE:         Critical sections
 * PROGRAMMERS:     Alex Ionescu (alex@relsoft.net)
 *                  Gunnar Dalsnes
 */

/* INCLUDES *****************************************************************/

#include <rtl.h>

#define NDEBUG
#include <debug.h>

#define MAX_STATIC_CS_DEBUG_OBJECTS 64

static RTL_CRITICAL_SECTION RtlCriticalSectionLock;
static LIST_ENTRY RtlCriticalSectionList = {&RtlCriticalSectionList, &RtlCriticalSectionList};
static BOOLEAN RtlpCritSectInitialized = FALSE;
static RTL_CRITICAL_SECTION_DEBUG RtlpStaticDebugInfo[MAX_STATIC_CS_DEBUG_OBJECTS];
static BOOLEAN RtlpDebugInfoFreeList[MAX_STATIC_CS_DEBUG_OBJECTS];

LARGE_INTEGER RtlpTimeout;
BOOLEAN RtlpTimeoutDisable;

extern BOOLEAN LdrpShutdownInProgress;
extern HANDLE LdrpShutdownThreadId;

/* FUNCTIONS *****************************************************************/

#define CRITSECT_HAS_DEBUG_INFO(CriticalSection) \
    (((CriticalSection)->DebugInfo != NULL) && \
     ((CriticalSection)->DebugInfo != LongToPtr(-1)))

/*++
 * RtlpCreateCriticalSectionSem
 *
 *     Checks if an Event has been created for the critical section.
 *
 * Params:
 *     None
 *
 * Returns:
 *     None. Raises an exception if the system call failed.
 *
 * Remarks:
 *     None
 *
 *--*/
_At_(CriticalSection->LockSemaphore, _Post_notnull_)
VOID
NTAPI
RtlpCreateCriticalSectionSem(PRTL_CRITICAL_SECTION CriticalSection)
{
    HANDLE hEvent = CriticalSection->LockSemaphore;
    HANDLE hNewEvent;
    NTSTATUS Status;

    /* Check if we have an event */
    if (!hEvent)
    {
        /* No, so create it */
        Status = NtCreateEvent(&hNewEvent,
                               EVENT_ALL_ACCESS,
                               NULL,
                               SynchronizationEvent,
                               FALSE);
        if (!NT_SUCCESS(Status))
        {
            DPRINT1("Failed to Create Event!\n");

            /*
             * Use INVALID_HANDLE_VALUE (-1) to signal that
             * the global keyed event must be used.
             */
            hNewEvent = INVALID_HANDLE_VALUE;
        }

        DPRINT("Created Event: %p\n", hNewEvent);

        /* Exchange the LockSemaphore field with the new handle, if it is still 0 */
        if (InterlockedCompareExchangePointer((PVOID*)&CriticalSection->LockSemaphore,
                                              (PVOID)hNewEvent,
                                               NULL) != NULL)
        {
            /* Someone else just created an event */
            if (hNewEvent != INVALID_HANDLE_VALUE)
            {
                DPRINT("Closing already created event: %p\n", hNewEvent);
                NtClose(hNewEvent);
            }
        }
    }

    return;
}

/*++
 * RtlpWaitForCriticalSection
 *
 *     Slow path of RtlEnterCriticalSection. Waits on an Event Object.
 *
 * Params:
 *     CriticalSection - Critical section to acquire.
 *
 * Returns:
 *     STATUS_SUCCESS, or raises an exception if a deadlock is occuring.
 *
 * Remarks:
 *     None
 *
 *--*/
NTSTATUS
NTAPI
RtlpWaitForCriticalSection(PRTL_CRITICAL_SECTION CriticalSection)
{
    NTSTATUS Status;
    EXCEPTION_RECORD ExceptionRecord;
    BOOLEAN LastChance = FALSE;

    /* Increase the Debug Entry count */
    DPRINT("Waiting on Critical Section Event: %p %p\n",
            CriticalSection,
            CriticalSection->LockSemaphore);

    if (CRITSECT_HAS_DEBUG_INFO(CriticalSection))
        CriticalSection->DebugInfo->EntryCount++;

    /*
     * If we're shutting down the process, we're allowed to acquire any
     * critical sections by force (the loader lock in particular)
     */
    if (LdrpShutdownInProgress &&
        LdrpShutdownThreadId == NtCurrentTeb()->RealClientId.UniqueThread)
    {
        DPRINT("Forcing ownership of critical section %p\n", CriticalSection);
        return STATUS_SUCCESS;
    }

    /* Do we have an Event yet? */
    if (!CriticalSection->LockSemaphore)
    {
        RtlpCreateCriticalSectionSem(CriticalSection);
    }

    for (;;)
    {
        /* Increase the number of times we've had contention */
        if (CRITSECT_HAS_DEBUG_INFO(CriticalSection))
            CriticalSection->DebugInfo->ContentionCount++;

        /* Check if allocating the event failed */
        if (CriticalSection->LockSemaphore == INVALID_HANDLE_VALUE)
        {
            /* Use the global keyed event (NULL as keyed event handle) */
            Status = NtWaitForKeyedEvent(NULL,
                                         CriticalSection,
                                         FALSE,
                                         (RtlpTimeoutDisable ? NULL : &RtlpTimeout));
        }
        else
        {
            /* Wait on the Event */
            Status = NtWaitForSingleObject(CriticalSection->LockSemaphore,
                                           FALSE,
                                           (RtlpTimeoutDisable ? NULL : &RtlpTimeout));
        }

        /* We have Timed out */
        if (Status == STATUS_TIMEOUT)
        {
            /* Is this the 2nd time we've timed out? */
            if (LastChance)
            {
                ERROR_DBGBREAK("Deadlock: 0x%p\n", CriticalSection);

                /* Yes it is, we are raising an exception */
                ExceptionRecord.ExceptionCode    = STATUS_POSSIBLE_DEADLOCK;
                ExceptionRecord.ExceptionFlags   = 0;
                ExceptionRecord.ExceptionRecord  = NULL;
                ExceptionRecord.ExceptionAddress = RtlRaiseException;
                ExceptionRecord.NumberParameters = 1;
                ExceptionRecord.ExceptionInformation[0] = (ULONG_PTR)CriticalSection;
                RtlRaiseException(&ExceptionRecord);
            }

            /* One more try */
            LastChance = TRUE;
        }
        else
        {
            /* If we are here, everything went fine */
            return STATUS_SUCCESS;
        }
    }
}

/*++
 * RtlpUnWaitCriticalSection
 *
 *     Slow path of RtlLeaveCriticalSection. Fires an Event Object.
 *
 * Params:
 *     CriticalSection - Critical section to release.
 *
 * Returns:
 *     None. Raises an exception if the system call failed.
 *
 * Remarks:
 *     None
 *
 *--*/
VOID
NTAPI
RtlpUnWaitCriticalSection(PRTL_CRITICAL_SECTION CriticalSection)
{
    NTSTATUS Status;

    /* Do we have an Event yet? */
    if (!CriticalSection->LockSemaphore)
    {
        RtlpCreateCriticalSectionSem(CriticalSection);
    }

    /* Signal the Event */
    DPRINT("Signaling Critical Section Event: %p, %p\n",
            CriticalSection,
            CriticalSection->LockSemaphore);

    /* Check if this critical section needs to use the keyed event */
    if (CriticalSection->LockSemaphore == INVALID_HANDLE_VALUE)
    {
        /* Release keyed event */
        Status = NtReleaseKeyedEvent(NULL, CriticalSection, FALSE, &RtlpTimeout);
    }
    else
    {
        /* Set the event */
        Status = NtSetEvent(CriticalSection->LockSemaphore, NULL);
    }

    if (!NT_SUCCESS(Status))
    {
        /* We've failed */
        DPRINT1("Signaling Failed for: %p, %p, 0x%08lx\n",
                CriticalSection,
                CriticalSection->LockSemaphore,
                Status);
        RtlRaiseStatus(Status);
    }
}

/*++
 * RtlpInitDeferredCriticalSection
 *
 *     Initializes the Critical Section implementation.
 *
 * Params:
 *     None
 *
 * Returns:
 *     None.
 *
 * Remarks:
 *     After this call, the Process Critical Section list is protected.
 *
 *--*/
VOID
NTAPI
RtlpInitDeferredCriticalSection(VOID)
{
    /* Initialize the CS Protecting the List */
    RtlInitializeCriticalSection(&RtlCriticalSectionLock);

    /* It's now safe to enter it */
    RtlpCritSectInitialized = TRUE;
}

/*++
 * RtlpAllocateDebugInfo
 *
 *     Finds or allocates memory for a Critical Section Debug Object
 *
 * Params:
 *     None
 *
 * Returns:
 *     A pointer to an empty Critical Section Debug Object.
 *
 * Remarks:
 *     For optimization purposes, the first 64 entries can be cached. From
 *     then on, future Critical Sections will allocate memory from the heap.
 *
 *--*/
PRTL_CRITICAL_SECTION_DEBUG
NTAPI
RtlpAllocateDebugInfo(VOID)
{
    ULONG i;

    /* Try to allocate from our buffer first */
    for (i = 0; i < MAX_STATIC_CS_DEBUG_OBJECTS; i++)
    {
        /* Check if Entry is free */
        if (!RtlpDebugInfoFreeList[i])
        {
            /* Mark entry in use */
            DPRINT("Using entry: %lu. Buffer: %p\n", i, &RtlpStaticDebugInfo[i]);
            RtlpDebugInfoFreeList[i] = TRUE;

            /* Use free entry found */
            return &RtlpStaticDebugInfo[i];
        }
    }

    /* We are out of static buffer, allocate dynamic */
    return RtlAllocateHeap(RtlGetProcessHeap(),
                           0,
                           sizeof(RTL_CRITICAL_SECTION_DEBUG));
}

/*++
 * RtlpFreeDebugInfo
 *
 *     Frees the memory for a Critical Section Debug Object
 *
 * Params:
 *     DebugInfo - Pointer to Critical Section Debug Object to free.
 *
 * Returns:
 *     None.
 *
 * Remarks:
 *     If the pointer is part of the static buffer, then the entry is made
 *     free again. If not, the object is de-allocated from the heap.
 *
 *--*/
VOID
NTAPI
RtlpFreeDebugInfo(PRTL_CRITICAL_SECTION_DEBUG DebugInfo)
{
    SIZE_T EntryId;

    /* Is it part of our cached entries? */
    if ((DebugInfo >= RtlpStaticDebugInfo) &&
        (DebugInfo <= &RtlpStaticDebugInfo[MAX_STATIC_CS_DEBUG_OBJECTS-1]))
    {
        /* Yes. zero it out */
        RtlZeroMemory(DebugInfo, sizeof(RTL_CRITICAL_SECTION_DEBUG));

        /* Mark as free */
        EntryId = (DebugInfo - RtlpStaticDebugInfo);
        DPRINT("Freeing from Buffer: %p. Entry: %Iu inside Process: %p\n",
               DebugInfo,
               EntryId,
               NtCurrentTeb()->ClientId.UniqueProcess);
        RtlpDebugInfoFreeList[EntryId] = FALSE;

    }
    else if (!DebugInfo->Flags)
    {
        /* It's a dynamic one, so free from the heap */
        DPRINT("Freeing from Heap: %p inside Process: %p\n",
               DebugInfo,
               NtCurrentTeb()->ClientId.UniqueProcess);
        RtlFreeHeap(NtCurrentPeb()->ProcessHeap, 0, DebugInfo);
    }
    else
    {
        /* Wine stores a section name pointer in the Flags member */
        DPRINT("Assuming static: %p inside Process: %p\n",
               DebugInfo,
               NtCurrentTeb()->ClientId.UniqueProcess);
    }
}

/*++
 * RtlDeleteCriticalSection
 * @implemented NT4
 *
 *     Deletes a Critical Section
 *
 * Params:
 *     CriticalSection - Critical section to delete.
 *
 * Returns:
 *     STATUS_SUCCESS, or error value returned by NtClose.
 *
 * Remarks:
 *     The critical section members should not be read after this call.
 *
 *--*/
NTSTATUS
NTAPI
RtlDeleteCriticalSection(PRTL_CRITICAL_SECTION CriticalSection)
{
    NTSTATUS Status = STATUS_SUCCESS;

    DPRINT("Deleting Critical Section: %p\n", CriticalSection);

    /* Close the Event Object Handle if it exists */
    if (CriticalSection->LockSemaphore)
    {
        /* In case NtClose fails, return the status */
        Status = NtClose(CriticalSection->LockSemaphore);
    }

    /* Protect List */
    RtlEnterCriticalSection(&RtlCriticalSectionLock);

    if (CRITSECT_HAS_DEBUG_INFO(CriticalSection))
    {
        /* Remove it from the list */
        RemoveEntryList(&CriticalSection->DebugInfo->ProcessLocksList);
#if 0
        /* We need to preserve Flags for RtlpFreeDebugInfo */
        RtlZeroMemory(CriticalSection->DebugInfo, sizeof(RTL_CRITICAL_SECTION_DEBUG));
#endif
    }

    /* Unprotect */
    RtlLeaveCriticalSection(&RtlCriticalSectionLock);

    if (CRITSECT_HAS_DEBUG_INFO(CriticalSection))
    {
        /* Free it */
        RtlpFreeDebugInfo(CriticalSection->DebugInfo);
    }

    /* Wipe it out */
    RtlZeroMemory(CriticalSection, sizeof(RTL_CRITICAL_SECTION));

    /* Return */
    return Status;
}

/*++
 * RtlSetCriticalSectionSpinCount
 * @implemented NT4
 *
 *     Sets the spin count for a critical section.
 *
 * Params:
 *     CriticalSection - Critical section to set the spin count for.
 *
 *     SpinCount - Spin count for the critical section.
 *
 * Returns:
 *     STATUS_SUCCESS.
 *
 * Remarks:
 *     SpinCount is ignored on single-processor systems.
 *
 *--*/
ULONG
NTAPI
RtlSetCriticalSectionSpinCount(PRTL_CRITICAL_SECTION CriticalSection,
                               ULONG SpinCount)
{
    ULONG OldCount = (ULONG)CriticalSection->SpinCount;

    /* Set to parameter if MP, or to 0 if this is Uniprocessor */
    CriticalSection->SpinCount = (NtCurrentPeb()->NumberOfProcessors > 1) ? SpinCount : 0;
    return OldCount;
}

/*++
 * RtlEnterCriticalSection
 * @implemented NT4
 *
 *     Waits to gain ownership of the critical section.
 *
 * Params:
 *     CriticalSection - Critical section to wait for.
 *
 * Returns:
 *     STATUS_SUCCESS.
 *
 * Remarks:
 *     Uses a fast-path unless contention happens.
 *
 *--*/
NTSTATUS
NTAPI
RtlEnterCriticalSection(PRTL_CRITICAL_SECTION CriticalSection)
{
    HANDLE Thread = (HANDLE)NtCurrentTeb()->ClientId.UniqueThread;

    /* Try to lock it */
    if (InterlockedIncrement(&CriticalSection->LockCount) != 0)
    {
        /* We've failed to lock it! Does this thread actually own it? */
        if (Thread == CriticalSection->OwningThread)
        {
            /*
             * You own it, so you'll get it when you're done with it! No need to
             * use the interlocked functions as only the thread who already owns
             * the lock can modify this data.
             */
            CriticalSection->RecursionCount++;
            return STATUS_SUCCESS;
        }

        /* NOTE - CriticalSection->OwningThread can be NULL here because changing
                  this information is not serialized. This happens when thread a
                  acquires the lock (LockCount == 0) and thread b tries to
                  acquire it as well (LockCount == 1) but thread a hasn't had a
                  chance to set the OwningThread! So it's not an error when
                  OwningThread is NULL here! */

        /* We don't own it, so we must wait for it */
        RtlpWaitForCriticalSection(CriticalSection);
    }

    /*
     * Lock successful. Changing this information has not to be serialized
     * because only one thread at a time can actually change it (the one who
     * acquired the lock)!
     */
    CriticalSection->OwningThread = Thread;
    CriticalSection->RecursionCount = 1;
    return STATUS_SUCCESS;
}

/*++
 * RtlInitializeCriticalSection
 * @implemented NT4
 *
 *     Initialises a new critical section.
 *
 * Params:
 *     CriticalSection - Critical section to initialise
 *
 * Returns:
 *     STATUS_SUCCESS.
 *
 * Remarks:
 *     Simply calls RtlInitializeCriticalSectionAndSpinCount
 *
 *--*/
NTSTATUS
NTAPI
RtlInitializeCriticalSection(PRTL_CRITICAL_SECTION CriticalSection)
{
    /* Call the Main Function */
    return RtlInitializeCriticalSectionAndSpinCount(CriticalSection, 0);
}

/*++
 * RtlInitializeCriticalSectionEx
 * @implemented NT6.0
 *
 *     Initialises a new critical section.
 *
 * Params:
 *     CriticalSection - Critical section to initialise
 *
 *     SpinCount - Spin count for the critical section.
 *
 *     Flags - Flags for initialization.
 *
 * Returns:
 *     STATUS_SUCCESS.
 *
 * Remarks:
 *     SpinCount is ignored on single-processor systems.
 *
 *--*/
NTSTATUS
NTAPI
RtlInitializeCriticalSectionEx(
    _Out_ PRTL_CRITICAL_SECTION CriticalSection,
    _In_ ULONG SpinCount,
    _In_ ULONG Flags)
{
    PRTL_CRITICAL_SECTION_DEBUG CritcalSectionDebugData;
    ULONG AllowedFlags;
    ULONG OsVersion;

    /* Remove lower bits from flags */
    Flags &= RTL_CRITICAL_SECTION_ALL_FLAG_BITS;

    /* These flags generally allowed */
    AllowedFlags = RTL_CRITICAL_SECTION_FLAG_NO_DEBUG_INFO |
                   RTL_CRITICAL_SECTION_FLAG_DYNAMIC_SPIN |
                   RTL_CRITICAL_SECTION_FLAG_STATIC_INIT;

    /* Flags for Windows 7+ (CHECKME) */
    OsVersion = NtCurrentPeb()->OSMajorVersion << 8 |
                NtCurrentPeb()->OSMinorVersion;
    if (OsVersion >= _WIN32_WINNT_WIN7)
    {
        AllowedFlags |= RTL_CRITICAL_SECTION_FLAG_RESOURCE_TYPE |
                        RTL_CRITICAL_SECTION_FLAG_FORCE_DEBUG_INFO;
    }

    if (Flags & ~AllowedFlags)
    {
        return STATUS_INVALID_PARAMETER_3;
    }

    if (SpinCount & RTL_CRITICAL_SECTION_ALL_FLAG_BITS)
    {
        return STATUS_INVALID_PARAMETER_2;
    }

    /* First things first, set up the Object */
    DPRINT("Initializing Critical Section: %p\n", CriticalSection);
    CriticalSection->LockCount = -1;
    CriticalSection->RecursionCount = 0;
    CriticalSection->OwningThread = 0;
    CriticalSection->SpinCount = (NtCurrentPeb()->NumberOfProcessors > 1) ? SpinCount : 0;
    CriticalSection->LockSemaphore = 0;

    if (Flags & RTL_CRITICAL_SECTION_FLAG_NO_DEBUG_INFO)
    {
        CriticalSection->DebugInfo = LongToPtr(-1);
    }
    else
    {
        /* Allocate the Debug Data */
        CritcalSectionDebugData = RtlpAllocateDebugInfo();
        DPRINT("Allocated Debug Data: %p inside Process: %p\n",
               CritcalSectionDebugData,
               NtCurrentTeb()->ClientId.UniqueProcess);

        if (!CritcalSectionDebugData)
        {
            /* This is bad! */
            DPRINT1("Couldn't allocate Debug Data for: %p\n", CriticalSection);
            return STATUS_NO_MEMORY;
        }

        /* Set it up */
        CritcalSectionDebugData->Type = RTL_CRITSECT_TYPE;
        CritcalSectionDebugData->ContentionCount = 0;
        CritcalSectionDebugData->EntryCount = 0;
        CritcalSectionDebugData->CriticalSection = CriticalSection;
        CritcalSectionDebugData->Flags = 0;
        CriticalSection->DebugInfo = CritcalSectionDebugData;

        /*
         * Add it to the List of Critical Sections owned by the process.
         * If we've initialized the Lock, then use it. If not, then probably
         * this is the lock initialization itself, so insert it directly.
         */
        if ((CriticalSection != &RtlCriticalSectionLock) && (RtlpCritSectInitialized))
        {
            DPRINT("Securely Inserting into ProcessLocks: %p, %p, %p\n",
                   &CritcalSectionDebugData->ProcessLocksList,
                   CriticalSection,
                   &RtlCriticalSectionList);

            /* Protect List */
            RtlEnterCriticalSection(&RtlCriticalSectionLock);

            /* Add this one */
            InsertTailList(&RtlCriticalSectionList, &CritcalSectionDebugData->ProcessLocksList);

            /* Unprotect */
            RtlLeaveCriticalSection(&RtlCriticalSectionLock);
        }
        else
        {
            DPRINT("Inserting into ProcessLocks: %p, %p, %p\n",
                   &CritcalSectionDebugData->ProcessLocksList,
                   CriticalSection,
                   &RtlCriticalSectionList);

            /* Add it directly */
            InsertTailList(&RtlCriticalSectionList, &CritcalSectionDebugData->ProcessLocksList);
        }
    }

    return STATUS_SUCCESS;
}

/*++
 * RtlInitializeCriticalSectionAndSpinCount
 * @implemented NT4
 *
 *     Initialises a new critical section.
 *
 * Params:
 *     CriticalSection - Critical section to initialise
 *
 *     SpinCount - Spin count for the critical section.
 *
 * Returns:
 *     STATUS_SUCCESS.
 *
 * Remarks:
 *     SpinCount is ignored on single-processor systems.
 *
 *--*/
NTSTATUS
NTAPI
RtlInitializeCriticalSectionAndSpinCount(
    _Out_ PRTL_CRITICAL_SECTION CriticalSection,
    _In_ ULONG SpinCount)
{
    SpinCount &= ~RTL_CRITICAL_SECTION_ALL_FLAG_BITS;
    return RtlInitializeCriticalSectionEx(CriticalSection, SpinCount, 0);
}

/*++
 * RtlGetCriticalSectionRecursionCount
 * @implemented NT5.2 SP1
 *
 *     Retrieves the recursion count of a given critical section.
 *
 * Params:
 *     CriticalSection - Critical section to retrieve its recursion count.
 *
 * Returns:
 *     The recursion count.
 *
 * Remarks:
 *     We return the recursion count of the critical section if it is owned
 *     by the current thread, and otherwise we return zero.
 *
 *--*/
LONG
NTAPI
RtlGetCriticalSectionRecursionCount(PRTL_CRITICAL_SECTION CriticalSection)
{
    if (CriticalSection->OwningThread == NtCurrentTeb()->ClientId.UniqueThread)
    {
        /*
         * The critical section is owned by the current thread,
         * therefore retrieve its actual recursion count.
         */
        return CriticalSection->RecursionCount;
    }
    else
    {
        /*
         * It is not owned by the current thread, so
         * for this thread there is no recursion.
         */
        return 0;
    }
}

/*++
 * RtlLeaveCriticalSection
 * @implemented NT4
 *
 *     Releases a critical section and makes if available for new owners.
 *
 * Params:
 *     CriticalSection - Critical section to release.
 *
 * Returns:
 *     STATUS_SUCCESS.
 *
 * Remarks:
 *     If another thread was waiting, the slow path is entered.
 *
 *--*/
NTSTATUS
NTAPI
RtlLeaveCriticalSection(PRTL_CRITICAL_SECTION CriticalSection)
{
#if DBG
    HANDLE Thread = (HANDLE)NtCurrentTeb()->ClientId.UniqueThread;

    /*
     * In win this case isn't checked. However it's a valid check so it should
     * only be performed in debug builds!
     */
    if (Thread != CriticalSection->OwningThread)
    {
       DPRINT1("Releasing critical section not owned!\n");
       return STATUS_INVALID_PARAMETER;
    }
#endif

    /*
     * Decrease the Recursion Count. No need to do this atomically because only
     * the thread who holds the lock can call this function (unless the program
     * is totally screwed...
     */
    if (--CriticalSection->RecursionCount)
    {
        if (CriticalSection->RecursionCount < 0)
        {
            DPRINT1("CRITICAL SECTION MESS: Section %p is not acquired!\n", CriticalSection);
            return STATUS_UNSUCCESSFUL;
        }
        /* Someone still owns us, but we are free. This needs to be done atomically. */
        InterlockedDecrement(&CriticalSection->LockCount);
    }
    else
    {
        /*
         * Nobody owns us anymore. No need to do this atomically.
         * See comment above.
         */
        CriticalSection->OwningThread = 0;

        /* Was someone wanting us? This needs to be done atomically. */
        if (-1 != InterlockedDecrement(&CriticalSection->LockCount))
        {
            /* Let him have us */
            RtlpUnWaitCriticalSection(CriticalSection);
        }
    }

    /* Sucessful! */
    return STATUS_SUCCESS;
}

/*++
 * RtlTryEnterCriticalSection
 * @implemented NT4
 *
 *     Attemps to gain ownership of the critical section without waiting.
 *
 * Params:
 *     CriticalSection - Critical section to attempt acquiring.
 *
 * Returns:
 *     TRUE if the critical section has been acquired, FALSE otherwise.
 *
 * Remarks:
 *     None
 *
 *--*/
BOOLEAN
NTAPI
RtlTryEnterCriticalSection(PRTL_CRITICAL_SECTION CriticalSection)
{
    /* Try to take control */
    if (InterlockedCompareExchange(&CriticalSection->LockCount, 0, -1) == -1)
    {
        /* It's ours */
        CriticalSection->OwningThread =  NtCurrentTeb()->ClientId.UniqueThread;
        CriticalSection->RecursionCount = 1;
        return TRUE;
    }
    else if (CriticalSection->OwningThread == NtCurrentTeb()->ClientId.UniqueThread)
    {
        /* It's already ours */
        InterlockedIncrement(&CriticalSection->LockCount);
        CriticalSection->RecursionCount++;
        return TRUE;
    }

    /* It's not ours */
    return FALSE;
}

VOID
NTAPI
RtlCheckForOrphanedCriticalSections(HANDLE ThreadHandle)
{
    UNIMPLEMENTED;
}

ULONG
NTAPI
RtlIsCriticalSectionLocked(PRTL_CRITICAL_SECTION CriticalSection)
{
    return CriticalSection->RecursionCount != 0;
}

ULONG
NTAPI
RtlIsCriticalSectionLockedByThread(PRTL_CRITICAL_SECTION CriticalSection)
{
    return CriticalSection->OwningThread == NtCurrentTeb()->ClientId.UniqueThread &&
           CriticalSection->RecursionCount != 0;
}

VOID
NTAPI
RtlpNotOwnerCriticalSection(PRTL_CRITICAL_SECTION CriticalSection)
{
    RtlRaiseStatus(STATUS_RESOURCE_NOT_OWNED);
}

/* EOF */