RTDECL(int) RTPipeRead(RTPIPE hPipe, void *pvBuf, size_t cbToRead, size_t *pcbRead)
{
    RTPIPEINTERNAL *pThis = hPipe;
    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
    AssertReturn(pThis->u32Magic == RTPIPE_MAGIC, VERR_INVALID_HANDLE);
    AssertReturn(pThis->fRead, VERR_ACCESS_DENIED);
    AssertPtr(pcbRead);
    AssertPtr(pvBuf);

    int rc = rtPipeTryNonBlocking(pThis);
    if (RT_SUCCESS(rc))
    {
        ssize_t cbRead = read(pThis->fd, pvBuf, RT_MIN(cbToRead, SSIZE_MAX));
        if (cbRead >= 0)
        {
            if (cbRead || !cbToRead || !rtPipePosixHasHup(pThis))
                *pcbRead = cbRead;
            else
                rc = VERR_BROKEN_PIPE;
        }
        else if (errno == EAGAIN)
        {
            *pcbRead = 0;
            rc = VINF_TRY_AGAIN;
        }
        else
            rc = RTErrConvertFromErrno(errno);

        ASMAtomicDecU32(&pThis->u32State);
    }
    return rc;
}

/**
 *  Uninitializes the instance and sets the ready flag to FALSE.
 *  Called either from FinalRelease() or by the parent when it gets destroyed.
 */
void VirtualBoxClient::uninit()
{
    LogFlowThisFunc(("\n"));

    /* Enclose the state transition Ready->InUninit->NotReady */
    AutoUninitSpan autoUninitSpan(this);
    if (autoUninitSpan.uninitDone())
        return;

    if (mData.m_ThreadWatcher != NIL_RTTHREAD)
    {
        /* Signal the event semaphore and wait for the thread to terminate.
         * if it hangs for some reason exit anyway, this can cause a crash
         * though as the object will no longer be available. */
        RTSemEventSignal(mData.m_SemEvWatcher);
        RTThreadWait(mData.m_ThreadWatcher, 30000, NULL);
        mData.m_ThreadWatcher = NIL_RTTHREAD;
        RTSemEventDestroy(mData.m_SemEvWatcher);
        mData.m_SemEvWatcher = NIL_RTSEMEVENT;
    }

    mData.m_pVirtualBox.setNull();

    ASMAtomicDecU32(&g_cInstances);
}

int vboxVhwaHlpCheckTerm(PVBOXMP_DEVEXT pDevExt, D3DDDI_VIDEO_PRESENT_SOURCE_ID VidPnSourceId)
{
    Assert(VidPnSourceId < (D3DDDI_VIDEO_PRESENT_SOURCE_ID)VBoxCommonFromDeviceExt(pDevExt)->cDisplays);
    if (VidPnSourceId >= (D3DDDI_VIDEO_PRESENT_SOURCE_ID)VBoxCommonFromDeviceExt(pDevExt)->cDisplays)
        return VERR_INVALID_PARAMETER;

    PVBOXWDDM_SOURCE pSource = &pDevExt->aSources[VidPnSourceId];

    Assert(!!(pSource->Vhwa.Settings.fFlags & VBOXVHWA_F_ENABLED));

    /** @todo need a better sync */
    uint32_t cNew = ASMAtomicDecU32(&pSource->Vhwa.cOverlaysCreated);
    int rc = VINF_SUCCESS;
    if (!cNew)
    {
        rc = vboxVhwaHlpDestroyPrimary(pDevExt, pSource, VidPnSourceId);
        AssertRC(rc);
    }
    else
    {
        Assert(cNew < UINT32_MAX / 2);
    }

    return rc;
}

RTDECL(int) RTPipeWrite(RTPIPE hPipe, const void *pvBuf, size_t cbToWrite, size_t *pcbWritten)
{
    RTPIPEINTERNAL *pThis = hPipe;
    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
    AssertReturn(pThis->u32Magic == RTPIPE_MAGIC, VERR_INVALID_HANDLE);
    AssertReturn(!pThis->fRead, VERR_ACCESS_DENIED);
    AssertPtr(pcbWritten);
    AssertPtr(pvBuf);

    int rc = rtPipeTryNonBlocking(pThis);
    if (RT_SUCCESS(rc))
    {
        if (cbToWrite)
        {
            ssize_t cbWritten = write(pThis->fd, pvBuf, RT_MIN(cbToWrite, SSIZE_MAX));
            if (cbWritten >= 0)
                *pcbWritten = cbWritten;
            else if (errno == EAGAIN)
            {
                *pcbWritten = 0;
                rc = VINF_TRY_AGAIN;
            }
            else
                rc = RTErrConvertFromErrno(errno);
        }
        else
            *pcbWritten = 0;

        ASMAtomicDecU32(&pThis->u32State);
    }
    return rc;
}

RTDECL(int)  RTSemMutexDestroy(RTSEMMUTEX hMutexSem)
{
    /*
     * Validate input.
     */
    PRTSEMMUTEXINTERNAL pThis = (PRTSEMMUTEXINTERNAL)hMutexSem;
    if (!pThis)
        return VERR_INVALID_PARAMETER;
    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
    AssertMsgReturn(pThis->u32Magic == RTSEMMUTEX_MAGIC, ("u32Magic=%RX32 pThis=%p\n", pThis->u32Magic, pThis), VERR_INVALID_HANDLE);
    RT_ASSERT_INTS_ON();

    /*
     * Kill it, wake up all waiting threads and release the reference.
     */
    AssertReturn(ASMAtomicCmpXchgU32(&pThis->u32Magic, ~RTSEMMUTEX_MAGIC, RTSEMMUTEX_MAGIC), VERR_INVALID_HANDLE);
    lck_spin_lock(pThis->pSpinlock);

    if (pThis->cWaiters > 0)
        thread_wakeup_prim((event_t)pThis, FALSE /* one_thread */, THREAD_RESTART);

    if (ASMAtomicDecU32(&pThis->cRefs) == 0)
        rtSemMutexDarwinFree(pThis);
    else
        lck_spin_unlock(pThis->pSpinlock);

    return VINF_SUCCESS;
}

/**
 * Releases a reference to a RTMPNTONSPECIFICARGS heap allocation, freeing it
 * when the last reference is released.
 */
DECLINLINE(void) rtMpNtOnSpecificRelease(PRTMPNTONSPECIFICARGS pArgs)
{
    uint32_t cRefs = ASMAtomicDecU32(&pArgs->cRefs);
    AssertMsg(cRefs <= 1, ("cRefs=%#x\n", cRefs));
    if (cRefs == 0)
        ExFreePool(pArgs);
}

/**
 * Release a reference, destroy the thing if necessary.
 *
 * @param   pThis       The semaphore.
 */
DECLINLINE(void) rtR0SemEventMultiHkuRelease(PRTSEMEVENTMULTIINTERNAL pThis)
{
    if (RT_UNLIKELY(ASMAtomicDecU32(&pThis->cRefs) == 0))
    {
        Assert(pThis->u32Magic != RTSEMEVENTMULTI_MAGIC);
        RTMemFree(pThis);
    }
}

 uint32_t i_release()
 {
     uint32_t cRefs = ASMAtomicDecU32(&m_cRefs);
     Assert(cRefs < _1K);
     if (cRefs == 0)
         delete this;
     return cRefs;
 }

void VBoxDispVHWACommandRelease(PVBOXDISPDEV pDev, VBOXVHWACMD* pCmd)
{
    uint32_t cRefs = ASMAtomicDecU32(&pCmd->cRefs);
    Assert(cRefs < UINT32_MAX / 2);
    if(!cRefs)
    {
        VBoxDispVHWACommandFree(pDev, pCmd);
    }
}

static uint32_t renderspuContextRelease( ContextInfo *context )
{
    uint32_t cRefs = ASMAtomicDecU32(&context->cRefs);
    if (!cRefs)
        renderspuDestroyContextTerminate( context );
    else
        CRASSERT(cRefs < UINT32_MAX/2);
    return cRefs;
}

static void vboxVhwaHlpOverlayListRemove(PVBOXMP_DEVEXT pDevExt, PVBOXWDDM_OVERLAY pOverlay)
{
    PVBOXWDDM_SOURCE pSource = &pDevExt->aSources[pOverlay->VidPnSourceId];
    KIRQL OldIrql;
    KeAcquireSpinLock(&pSource->OverlayListLock, &OldIrql);
    ASMAtomicDecU32(&pSource->cOverlays);
    RemoveEntryList(&pOverlay->ListEntry);
    KeReleaseSpinLock(&pSource->OverlayListLock, OldIrql);
}

/**
 * Release a reference, destroy the thing if necessary.
 *
 * @param   pThis       The semaphore.
 */
DECLINLINE(void) rtR0SemEventMultiDarwinRelease(PRTSEMEVENTMULTIINTERNAL pThis)
{
    if (RT_UNLIKELY(ASMAtomicDecU32(&pThis->cRefs) == 0))
    {
        Assert(pThis->u32Magic != RTSEMEVENTMULTI_MAGIC);
        lck_spin_destroy(pThis->pSpinlock, g_pDarwinLockGroup);
        RTMemFree(pThis);
    }
}

DECLINLINE(void) vbvaVhwaCommandRelease(PVBOXMP_DEVEXT pDevExt, VBOXVHWACMD* pCmd)
{
    uint32_t cRefs = ASMAtomicDecU32(&pCmd->cRefs);
    Assert(cRefs < UINT32_MAX / 2);
    if(!cRefs)
    {
        VBoxHGSMIBufferFree(&VBoxCommonFromDeviceExt(pDevExt)->guestCtx, pCmd);
    }
}

DECLINLINE(VOID) vboxWddmSwapchainRelease(PVBOXWDDM_SWAPCHAIN pSwapchain)
{
    const uint32_t cRefs = ASMAtomicDecU32(&pSwapchain->cRefs);
    Assert(cRefs < UINT32_MAX/2);
    if (!cRefs)
    {
        vboxWddmMemFree(pSwapchain);
    }
}

/**
 * Removes the thread from the AVL tree, call owns the tree lock
 * and has cleared the RTTHREADINT_FLAG_IN_TREE bit.
 *
 * @param   pThread     The thread to remove.
 */
static void rtThreadRemoveLocked(PRTTHREADINT pThread)
{
    PRTTHREADINT pThread2 = (PRTTHREADINT)RTAvlPVRemove(&g_ThreadTree, pThread->Core.Key);
#if !defined(RT_OS_OS2) /** @todo this asserts for threads created by NSPR */
    AssertMsg(pThread2 == pThread, ("%p(%s) != %p (%p/%s)\n", pThread2, pThread2  ? pThread2->szName : "<null>",
                                    pThread, pThread->Core.Key, pThread->szName));
#endif
    if (pThread2)
        ASMAtomicDecU32(&g_cThreadInTree);
}

RTDECL(int) RTSemMutexRelease(RTSEMMUTEX hMutexSem)
{
    /*
     * Validate input.
     */
    struct RTSEMMUTEXINTERNAL *pThis = hMutexSem;
    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
    AssertReturn(pThis->u32Magic == RTSEMMUTEX_MAGIC, VERR_INVALID_HANDLE);

#ifdef RTSEMMUTEX_STRICT
    int rc9 = RTLockValidatorRecExclReleaseOwner(&pThis->ValidatorRec, pThis->cNestings == 1);
    if (RT_FAILURE(rc9))
        return rc9;
#endif

    /*
     * Check if nested.
     */
    pthread_t Self = pthread_self();
    if (RT_UNLIKELY(    pThis->Owner != Self
                        ||  pThis->cNestings == 0))
    {
        AssertMsgFailed(("Not owner of mutex %p!! Self=%08x Owner=%08x cNestings=%d\n",
                         pThis, Self, pThis->Owner, pThis->cNestings));
        return VERR_NOT_OWNER;
    }

    /*
     * If nested we'll just pop a nesting.
     */
    if (pThis->cNestings > 1)
    {
        ASMAtomicDecU32(&pThis->cNestings);
        return VINF_SUCCESS;
    }

    /*
     * Clear the state. (cNestings == 1)
     */
    pThis->Owner = (pthread_t)~0;
    ASMAtomicWriteU32(&pThis->cNestings, 0);

    /*
     * Release the mutex.
     */
    int32_t iNew = ASMAtomicDecS32(&pThis->iState);
    if (RT_UNLIKELY(iNew != 0))
    {
        /* somebody is waiting, try wake up one of them. */
        ASMAtomicXchgS32(&pThis->iState, 0);
        (void)sys_futex(&pThis->iState, FUTEX_WAKE, 1, NULL, NULL, 0);
    }
    return VINF_SUCCESS;
}

/**
 * Releases the instance data.
 *
 * @param   pThis               The instance data.
 */
static void rtDbgModDeferredReleaseInstanceData(PRTDBGMODDEFERRED pThis)
{
    AssertPtr(pThis);
    uint32_t cRefs = ASMAtomicDecU32(&pThis->cRefs); Assert(cRefs < 8);
    if (!cRefs)
    {
        RTDbgCfgRelease(pThis->hDbgCfg);
        pThis->hDbgCfg = NIL_RTDBGCFG;
        RTMemFree(pThis);
    }
}

/**
 * Close a file device previously opened by VBoxDrvFreeBSDOpen
 *
 * @returns 0 on success.
 * @param   pDev        The device.
 * @param   fFile       The file descriptor flags.
 * @param   DevType     The device type (CHR.
 * @param   pTd         The calling thread.
 */
static void VBoxDrvFreeBSDDtr(void *pData)
{
    PSUPDRVSESSION pSession = pData;
    Log(("VBoxDrvFreeBSDDtr: pSession=%p\n", pSession));

    /*
     * Close the session.
     */
    supdrvSessionRelease(pSession);
    ASMAtomicDecU32(&g_cUsers);
}

uint32_t SecretKey::release()
{
    uint32_t cRefs = ASMAtomicDecU32(&m_cRefs);
    if (!cRefs)
    {
        int rc = RTMemSaferScramble(m_pbKey, m_cbKey);
        AssertRC(rc);
    }

    return cRefs;
}

/**
 * Release a reference to the module.
 *
 * When the reference count reaches zero, the module is destroyed.
 *
 * @returns New reference count, UINT32_MAX on invalid handle (asserted).
 *
 * @param   hDbgMod         The module handle. The NIL handle is quietly ignored
 *                          and 0 is returned.
 *
 * @remarks Will not take any locks.
 */
RTDECL(uint32_t) RTDbgModRelease(RTDBGMOD hDbgMod)
{
    if (hDbgMod == NIL_RTDBGMOD)
        return 0;
    PRTDBGMODINT pDbgMod = hDbgMod;
    RTDBGMOD_VALID_RETURN_RC(pDbgMod, UINT32_MAX);

    uint32_t cRefs = ASMAtomicDecU32(&pDbgMod->cRefs);
    if (!cRefs)
        rtDbgModDestroy(pDbgMod);
    return cRefs;
}