VOID FASTCALL ExfAcquirePushLockShared ( PEX_PUSH_LOCK PushLock )
Definition at line 644 of file pushlock.c.
Referenced by ExAcquirePushLockShared().
{
    EX_PUSH_LOCK OldValue = *PushLock, NewValue;
    BOOLEAN NeedWake;
    DEFINE_WAIT_BLOCK(WaitBlock);

    /* Start main loop */
    for (;;)
    {
        /* Check if it's unlocked or if it's waiting without any sharers */
        if (!(OldValue.Locked) || (!(OldValue.Waiting) && (OldValue.Shared > 0)))
        {
            /* Check if anyone is waiting on it */
            if (!OldValue.Waiting)
            {
                /* Increase the share count and lock it */
                NewValue.Value = OldValue.Value | EX_PUSH_LOCK_LOCK;
                NewValue.Shared++;
            }
            else
            {
                /* Simply set the lock bit */
                NewValue.Value = OldValue.Value | EX_PUSH_LOCK_LOCK;
            }

            /* Sanity check */
            ASSERT(NewValue.Locked);

            /* Set the new value */
            NewValue.Ptr = InterlockedCompareExchangePointer(&PushLock->Ptr,
                                                             NewValue.Ptr,
                                                             OldValue.Ptr);
            if (NewValue.Value != OldValue.Value)
            {
                /* Retry */
                OldValue = *PushLock;
                continue;
            }

            /* Break out of the loop */
            break;
        }
        else
        {
            /* We'll have to create a Waitblock */
            WaitBlock->Flags = EX_PUSH_LOCK_FLAGS_WAIT;
            WaitBlock->ShareCount = 0;
            NeedWake = FALSE;
            WaitBlock->Previous = NULL;

            /* Check if there is already a waiter */
            if (OldValue.Waiting)
            {
                /* Set the current Wait Block pointer */
                WaitBlock->Next = (PEX_PUSH_LOCK_WAIT_BLOCK)(
                                   OldValue.Value &~ EX_PUSH_LOCK_PTR_BITS);

                /* Nobody is the last waiter yet */
                WaitBlock->Last = NULL;

                /* Point to ours */
                NewValue.Value = (OldValue.Value & (EX_PUSH_LOCK_MULTIPLE_SHARED |
                                                    EX_PUSH_LOCK_LOCK)) |
                                  EX_PUSH_LOCK_WAKING |
                                  EX_PUSH_LOCK_WAITING |
                                  (ULONG_PTR)WaitBlock;

                /* Check if the pushlock was already waking */
                if (!OldValue.Waking) NeedWake = TRUE;
            }
            else
            {
                /* We are the first waiter, so loop the wait block */
                WaitBlock->Last = WaitBlock;

                /* Point to our wait block */
                NewValue.Value = (OldValue.Value & EX_PUSH_LOCK_PTR_BITS) |
                                  EX_PUSH_LOCK_WAITING |
                                  (ULONG_PTR)WaitBlock;
            }

            /* Sanity check */
            ASSERT(NewValue.Waiting);

#if DBG
            /* Setup the Debug Wait Block */
            WaitBlock->Signaled = 0;
            WaitBlock->OldValue = OldValue;
            WaitBlock->NewValue = NewValue;
            WaitBlock->PushLock = PushLock;
#endif

            /* Write the new value */
            NewValue.Ptr = InterlockedCompareExchangePointer(&PushLock->Ptr,
                                                             NewValue.Ptr,
                                                             OldValue.Ptr);
            if (NewValue.Ptr != OldValue.Ptr)
            {
                /* Retry */
                OldValue = *PushLock;
                continue;
            }

            /* Update the value now */
            OldValue = NewValue;

            /* Check if the pushlock needed waking */
            if (NeedWake)
            {
                /* Scan the Waiters and Wake PushLocks */
                ExpOptimizePushLockList(PushLock, OldValue);
            }

            /* Set up the Wait Gate */
            KeInitializeGate(&WaitBlock->WakeGate);

#ifdef CONFIG_SMP
            /* Now spin on the push lock if necessary */
            if (ExPushLockSpinCount)
            {
                ULONG i = ExPushLockSpinCount;

                do
                {
                    if (!(*(volatile LONG *)&WaitBlock->Flags & EX_PUSH_LOCK_WAITING))
                        break;

                    YieldProcessor();
                } while (--i);
            }
#endif

            /* Now try to remove the wait bit */
            if (InterlockedBitTestAndReset(&WaitBlock->Flags, 1))
            {
                /* Fast-path did not work, we need to do a full wait */
                KeWaitForGate(&WaitBlock->WakeGate, WrPushLock, KernelMode);
                ASSERT(WaitBlock->Signaled);
            }

            /* We shouldn't be shared anymore */
            ASSERT((WaitBlock->ShareCount == 0));
        }
    }
}
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