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reactos/lib/rtl/srw.c
Hermès Bélusca-Maïto f44e914e80 Sync with trunk r58033. 
svn path=/branches/ros-csrss/; revision=58034
2012-12-28 23:37:33 +00:00

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/*
* COPYRIGHT: See COPYING in the top level directory
* PROJECT: ReactOS system libraries
* PURPOSE: Slim Reader/Writer (SRW) Routines
* PROGRAMMER: Thomas Weidenmueller <w3seek@reactos.com>
*
* NOTES: The algorithms used in this implementation
* may be different from Vista's implementation.
* Since applications should treat the RTL_SRWLOCK
* structure as opaque data, it should not matter.
* The algorithms are probably not as optimized.
*/
/* INCLUDES *****************************************************************/
#include <rtl.h>
#define NDEBUG
#include <debug.h>
/* FUNCTIONS *****************************************************************/
#ifdef _WIN64
#define InterlockedBitTestAndSetPointer(ptr,val) InterlockedBitTestAndSet64((PLONGLONG)ptr,(LONGLONG)val)
#define InterlockedAddPointer(ptr,val) InterlockedAdd64((PLONGLONG)ptr,(LONGLONG)val)
#define InterlockedAndPointer(ptr,val) InterlockedAnd64((PLONGLONG)ptr,(LONGLONG)val)
#define InterlockedOrPointer(ptr,val) InterlockedOr64((PLONGLONG)ptr,(LONGLONG)val)
#else
#define InterlockedBitTestAndSetPointer(ptr,val) InterlockedBitTestAndSet((PLONG)ptr,(LONG)val)
#define InterlockedAddPointer(ptr,val) InterlockedAdd((PLONG)ptr,(LONG)val)
#define InterlockedAndPointer(ptr,val) InterlockedAnd((PLONG)ptr,(LONG)val)
#define InterlockedOrPointer(ptr,val) InterlockedOr((PLONG)ptr,(LONG)val)
#endif
#define RTL_SRWLOCK_OWNED_BIT 0
#define RTL_SRWLOCK_CONTENDED_BIT 1
#define RTL_SRWLOCK_SHARED_BIT 2
#define RTL_SRWLOCK_CONTENTION_LOCK_BIT 3
#define RTL_SRWLOCK_OWNED (1 << RTL_SRWLOCK_OWNED_BIT)
#define RTL_SRWLOCK_CONTENDED (1 << RTL_SRWLOCK_CONTENDED_BIT)
#define RTL_SRWLOCK_SHARED (1 << RTL_SRWLOCK_SHARED_BIT)
#define RTL_SRWLOCK_CONTENTION_LOCK (1 << RTL_SRWLOCK_CONTENTION_LOCK_BIT)
#define RTL_SRWLOCK_MASK (RTL_SRWLOCK_OWNED | RTL_SRWLOCK_CONTENDED | \
RTL_SRWLOCK_SHARED | RTL_SRWLOCK_CONTENTION_LOCK)
#define RTL_SRWLOCK_BITS 4
#if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__ < 40300) || \
(__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__ == 40303)
/* This macro will cause the code to assert if compiled with a buggy
version of GCC that doesn't align the wait blocks properly on the stack! */
#define ASSERT_SRW_WAITBLOCK(ptr) \
ASSERT(((ULONG_PTR)ptr & ((1 << RTL_SRWLOCK_BITS) - 1)) == 0)
#else
#define ASSERT_SRW_WAITBLOCK(ptr) ((void)0)
#endif
typedef struct _RTLP_SRWLOCK_SHARED_WAKE
{
LONG Wake;
volatile struct _RTLP_SRWLOCK_SHARED_WAKE *Next;
} volatile RTLP_SRWLOCK_SHARED_WAKE, *PRTLP_SRWLOCK_SHARED_WAKE;
typedef struct _RTLP_SRWLOCK_WAITBLOCK
{
/* SharedCount is the number of shared acquirers. */
LONG SharedCount;
/* Last points to the last wait block in the chain. The value
is only valid when read from the first wait block. */
volatile struct _RTLP_SRWLOCK_WAITBLOCK *Last;
/* Next points to the next wait block in the chain. */
volatile struct _RTLP_SRWLOCK_WAITBLOCK *Next;
union
{
/* Wake is only valid for exclusive wait blocks */
LONG Wake;
/* The wake chain is only valid for shared wait blocks */
struct
{
PRTLP_SRWLOCK_SHARED_WAKE SharedWakeChain;
PRTLP_SRWLOCK_SHARED_WAKE LastSharedWake;
};
};
BOOLEAN Exclusive;
} volatile RTLP_SRWLOCK_WAITBLOCK, *PRTLP_SRWLOCK_WAITBLOCK;
static VOID
NTAPI
RtlpReleaseWaitBlockLockExclusive(IN OUT PRTL_SRWLOCK SRWLock,
IN PRTLP_SRWLOCK_WAITBLOCK FirstWaitBlock)
{
PRTLP_SRWLOCK_WAITBLOCK Next;
LONG_PTR NewValue;
/* NOTE: We're currently in an exclusive lock in contended mode. */
Next = FirstWaitBlock->Next;
if (Next != NULL)
{
/* There's more blocks chained, we need to update the pointers
in the next wait block and update the wait block pointer. */
NewValue = (LONG_PTR)Next | RTL_SRWLOCK_OWNED | RTL_SRWLOCK_CONTENDED;
if (!FirstWaitBlock->Exclusive)
{
/* The next wait block has to be an exclusive lock! */
ASSERT(Next->Exclusive);
/* Save the shared count */
Next->SharedCount = FirstWaitBlock->SharedCount;
NewValue |= RTL_SRWLOCK_SHARED;
}
Next->Last = FirstWaitBlock->Last;
}
else
{
/* Convert the lock to a simple lock. */
if (FirstWaitBlock->Exclusive)
NewValue = RTL_SRWLOCK_OWNED;
else
{
ASSERT(FirstWaitBlock->SharedCount > 0);
NewValue = ((LONG_PTR)FirstWaitBlock->SharedCount << RTL_SRWLOCK_BITS) |
RTL_SRWLOCK_SHARED | RTL_SRWLOCK_OWNED;
}
}
(void)InterlockedExchangePointer(&SRWLock->Ptr, (PVOID)NewValue);
if (FirstWaitBlock->Exclusive)
{
(void)InterlockedOr(&FirstWaitBlock->Wake,
TRUE);
}
else
{
PRTLP_SRWLOCK_SHARED_WAKE WakeChain, NextWake;
/* If we were the first one to acquire the shared
lock, we now need to wake all others... */
WakeChain = FirstWaitBlock->SharedWakeChain;
do
{
NextWake = WakeChain->Next;
(void)InterlockedOr((PLONG)&WakeChain->Wake,
TRUE);
WakeChain = NextWake;
} while (WakeChain != NULL);
}
}
static VOID
NTAPI
RtlpReleaseWaitBlockLockLastShared(IN OUT PRTL_SRWLOCK SRWLock,
IN PRTLP_SRWLOCK_WAITBLOCK FirstWaitBlock)
{
PRTLP_SRWLOCK_WAITBLOCK Next;
LONG_PTR NewValue;
/* NOTE: We're currently in a shared lock in contended mode. */
/* The next acquirer to be unwaited *must* be an exclusive lock! */
ASSERT(FirstWaitBlock->Exclusive);
Next = FirstWaitBlock->Next;
if (Next != NULL)
{
/* There's more blocks chained, we need to update the pointers
in the next wait block and update the wait block pointer. */
NewValue = (LONG_PTR)Next | RTL_SRWLOCK_OWNED | RTL_SRWLOCK_CONTENDED;
Next->Last = FirstWaitBlock->Last;
}
else
{
/* Convert the lock to a simple exclusive lock. */
NewValue = RTL_SRWLOCK_OWNED;
}
(void)InterlockedExchangePointer(&SRWLock->Ptr, (PVOID)NewValue);
(void)InterlockedOr(&FirstWaitBlock->Wake,
TRUE);
}
static VOID
NTAPI
RtlpReleaseWaitBlockLock(IN OUT PRTL_SRWLOCK SRWLock)
{
InterlockedAndPointer(&SRWLock->Ptr,
~RTL_SRWLOCK_CONTENTION_LOCK);
}
static PRTLP_SRWLOCK_WAITBLOCK
NTAPI
RtlpAcquireWaitBlockLock(IN OUT PRTL_SRWLOCK SRWLock)
{
LONG_PTR PrevValue;
PRTLP_SRWLOCK_WAITBLOCK WaitBlock;
while (1)
{
PrevValue = InterlockedOrPointer(&SRWLock->Ptr,
RTL_SRWLOCK_CONTENTION_LOCK);
if (!(PrevValue & RTL_SRWLOCK_CONTENTION_LOCK))
break;
YieldProcessor();
}
if (!(PrevValue & RTL_SRWLOCK_CONTENDED) ||
(PrevValue & ~RTL_SRWLOCK_MASK) == 0)
{
/* Too bad, looks like the wait block was removed in the
meanwhile, unlock again */
RtlpReleaseWaitBlockLock(SRWLock);
return NULL;
}
WaitBlock = (PRTLP_SRWLOCK_WAITBLOCK)(PrevValue & ~RTL_SRWLOCK_MASK);
ASSERT_SRW_WAITBLOCK(WaitBlock);
return WaitBlock;
}
static VOID
NTAPI
RtlpAcquireSRWLockExclusiveWait(IN OUT PRTL_SRWLOCK SRWLock,
IN PRTLP_SRWLOCK_WAITBLOCK WaitBlock)
{
LONG_PTR CurrentValue;
while (1)
{
CurrentValue = *(volatile LONG_PTR *)&SRWLock->Ptr;
if (!(CurrentValue & RTL_SRWLOCK_SHARED))
{
if (CurrentValue & RTL_SRWLOCK_CONTENDED)
{
if (WaitBlock->Wake != 0)
{
/* Our wait block became the first one
in the chain, we own the lock now! */
break;
}
}
else
{
/* The last wait block was removed and/or we're
finally a simple exclusive lock. This means we
don't need to wait anymore, we acquired the lock! */
break;
}
}
YieldProcessor();
}
}
static VOID
NTAPI
RtlpAcquireSRWLockSharedWait(IN OUT PRTL_SRWLOCK SRWLock,
IN OUT PRTLP_SRWLOCK_WAITBLOCK FirstWait OPTIONAL,
IN OUT PRTLP_SRWLOCK_SHARED_WAKE WakeChain)
{
if (FirstWait != NULL)
{
while (WakeChain->Wake == 0)
{
YieldProcessor();
}
}
else
{
LONG_PTR CurrentValue;
while (1)
{
CurrentValue = *(volatile LONG_PTR *)&SRWLock->Ptr;
if (CurrentValue & RTL_SRWLOCK_SHARED)
{
/* The RTL_SRWLOCK_OWNED bit always needs to be set when
RTL_SRWLOCK_SHARED is set! */
ASSERT(CurrentValue & RTL_SRWLOCK_OWNED);
if (CurrentValue & RTL_SRWLOCK_CONTENDED)
{
if (WakeChain->Wake != 0)
{
/* Our wait block became the first one
in the chain, we own the lock now! */
break;
}
}
else
{
/* The last wait block was removed and/or we're
finally a simple shared lock. This means we
don't need to wait anymore, we acquired the lock! */
break;
}
}
YieldProcessor();
}
}
}
VOID
NTAPI
RtlInitializeSRWLock(OUT PRTL_SRWLOCK SRWLock)
{
SRWLock->Ptr = NULL;
}
VOID
NTAPI
RtlAcquireSRWLockShared(IN OUT PRTL_SRWLOCK SRWLock)
{
__ALIGNED(16) RTLP_SRWLOCK_WAITBLOCK StackWaitBlock;
RTLP_SRWLOCK_SHARED_WAKE SharedWake;
LONG_PTR CurrentValue, NewValue;
PRTLP_SRWLOCK_WAITBLOCK First, Shared, FirstWait;
while (1)
{
CurrentValue = *(volatile LONG_PTR *)&SRWLock->Ptr;
if (CurrentValue & RTL_SRWLOCK_SHARED)
{
/* NOTE: It is possible that the RTL_SRWLOCK_OWNED bit is set! */
if (CurrentValue & RTL_SRWLOCK_CONTENDED)
{
/* There's other waiters already, lock the wait blocks and
increment the shared count */
First = RtlpAcquireWaitBlockLock(SRWLock);
if (First != NULL)
{
FirstWait = NULL;
if (First->Exclusive)
{
/* We need to setup a new wait block! Although
we're currently in a shared lock and we're acquiring
a shared lock, there are exclusive locks queued. We need
to wait until those are released. */
Shared = First->Last;
if (Shared->Exclusive)
{
StackWaitBlock.Exclusive = FALSE;
StackWaitBlock.SharedCount = 1;
StackWaitBlock.Next = NULL;
StackWaitBlock.Last = &StackWaitBlock;
StackWaitBlock.SharedWakeChain = &SharedWake;
Shared->Next = &StackWaitBlock;
First->Last = &StackWaitBlock;
Shared = &StackWaitBlock;
FirstWait = &StackWaitBlock;
}
else
{
Shared->LastSharedWake->Next = &SharedWake;
Shared->SharedCount++;
}
}
else
{
Shared = First;
Shared->LastSharedWake->Next = &SharedWake;
Shared->SharedCount++;
}
SharedWake.Next = NULL;
SharedWake.Wake = 0;
Shared->LastSharedWake = &SharedWake;
ASSERT_SRW_WAITBLOCK(Shared);
RtlpReleaseWaitBlockLock(SRWLock);
RtlpAcquireSRWLockSharedWait(SRWLock,
FirstWait,
&SharedWake);
/* Successfully incremented the shared count, we acquired the lock */
break;
}
}
else
{
/* This is a fastest path, just increment the number of
current shared locks */
/* Since the RTL_SRWLOCK_SHARED bit is set, the RTL_SRWLOCK_OWNED bit also has
to be set! */
ASSERT(CurrentValue & RTL_SRWLOCK_OWNED);
NewValue = (CurrentValue >> RTL_SRWLOCK_BITS) + 1;
NewValue = (NewValue << RTL_SRWLOCK_BITS) | (CurrentValue & RTL_SRWLOCK_MASK);
if ((LONG_PTR)InterlockedCompareExchangePointer(&SRWLock->Ptr,
(PVOID)NewValue,
(PVOID)CurrentValue) == CurrentValue)
{
/* Successfully incremented the shared count, we acquired the lock */
break;
}
}
}
else
{
if (CurrentValue & RTL_SRWLOCK_OWNED)
{
/* The resource is currently acquired exclusively */
if (CurrentValue & RTL_SRWLOCK_CONTENDED)
{
SharedWake.Next = NULL;
SharedWake.Wake = 0;
/* There's other waiters already, lock the wait blocks and
increment the shared count. If the last block in the chain
is an exclusive lock, add another block. */
StackWaitBlock.Exclusive = FALSE;
StackWaitBlock.SharedCount = 0;
StackWaitBlock.Next = NULL;
StackWaitBlock.Last = &StackWaitBlock;
StackWaitBlock.SharedWakeChain = &SharedWake;
First = RtlpAcquireWaitBlockLock(SRWLock);
if (First != NULL)
{
Shared = First->Last;
if (Shared->Exclusive)
{
Shared->Next = &StackWaitBlock;
First->Last = &StackWaitBlock;
Shared = &StackWaitBlock;
FirstWait = &StackWaitBlock;
}
else
{
FirstWait = NULL;
Shared->LastSharedWake->Next = &SharedWake;
}
ASSERT_SRW_WAITBLOCK(Shared);
Shared->SharedCount++;
Shared->LastSharedWake = &SharedWake;
RtlpReleaseWaitBlockLock(SRWLock);
RtlpAcquireSRWLockSharedWait(SRWLock,
FirstWait,
&SharedWake);
/* Successfully incremented the shared count, we acquired the lock */
break;
}
}
else
{
SharedWake.Next = NULL;
SharedWake.Wake = 0;
/* We need to setup the first wait block. Currently an exclusive lock is
held, change the lock to contended mode. */
StackWaitBlock.Exclusive = FALSE;
StackWaitBlock.SharedCount = 1;
StackWaitBlock.Next = NULL;
StackWaitBlock.Last = &StackWaitBlock;
StackWaitBlock.SharedWakeChain = &SharedWake;
StackWaitBlock.LastSharedWake = &SharedWake;
ASSERT_SRW_WAITBLOCK(&StackWaitBlock);
NewValue = (ULONG_PTR)&StackWaitBlock | RTL_SRWLOCK_OWNED | RTL_SRWLOCK_CONTENDED;
if ((LONG_PTR)InterlockedCompareExchangePointer(&SRWLock->Ptr,
(PVOID)NewValue,
(PVOID)CurrentValue) == CurrentValue)
{
RtlpAcquireSRWLockSharedWait(SRWLock,
&StackWaitBlock,
&SharedWake);
/* Successfully set the shared count, we acquired the lock */
break;
}
}
}
else
{
/* This is a fast path, we can simply try to set the shared count to 1 */
NewValue = (1 << RTL_SRWLOCK_BITS) | RTL_SRWLOCK_SHARED | RTL_SRWLOCK_OWNED;
/* The RTL_SRWLOCK_CONTENDED bit should never be set if neither the
RTL_SRWLOCK_SHARED nor the RTL_SRWLOCK_OWNED bit is set */
ASSERT(!(CurrentValue & RTL_SRWLOCK_CONTENDED));
if ((LONG_PTR)InterlockedCompareExchangePointer(&SRWLock->Ptr,
(PVOID)NewValue,
(PVOID)CurrentValue) == CurrentValue)
{
/* Successfully set the shared count, we acquired the lock */
break;
}
}
}
YieldProcessor();
}
}
VOID
NTAPI
RtlReleaseSRWLockShared(IN OUT PRTL_SRWLOCK SRWLock)
{
LONG_PTR CurrentValue, NewValue;
PRTLP_SRWLOCK_WAITBLOCK WaitBlock;
BOOLEAN LastShared;
while (1)
{
CurrentValue = *(volatile LONG_PTR *)&SRWLock->Ptr;
if (CurrentValue & RTL_SRWLOCK_SHARED)
{
if (CurrentValue & RTL_SRWLOCK_CONTENDED)
{
/* There's a wait block, we need to wake a pending
exclusive acquirer if this is the last shared release */
WaitBlock = RtlpAcquireWaitBlockLock(SRWLock);
if (WaitBlock != NULL)
{
LastShared = (--WaitBlock->SharedCount == 0);
if (LastShared)
RtlpReleaseWaitBlockLockLastShared(SRWLock,
WaitBlock);
else
RtlpReleaseWaitBlockLock(SRWLock);
/* We released the lock */
break;
}
}
else
{
/* This is a fast path, we can simply decrement the shared
count and store the pointer */
NewValue = CurrentValue >> RTL_SRWLOCK_BITS;
if (--NewValue != 0)
{
NewValue = (NewValue << RTL_SRWLOCK_BITS) | RTL_SRWLOCK_SHARED | RTL_SRWLOCK_OWNED;
}
if ((LONG_PTR)InterlockedCompareExchangePointer(&SRWLock->Ptr,
(PVOID)NewValue,
(PVOID)CurrentValue) == CurrentValue)
{
/* Successfully released the lock */
break;
}
}
}
else
{
/* The RTL_SRWLOCK_SHARED bit has to be present now,
even in the contended case! */
RtlRaiseStatus(STATUS_RESOURCE_NOT_OWNED);
}
YieldProcessor();
}
}
VOID
NTAPI
RtlAcquireSRWLockExclusive(IN OUT PRTL_SRWLOCK SRWLock)
{
__ALIGNED(16) RTLP_SRWLOCK_WAITBLOCK StackWaitBlock;
PRTLP_SRWLOCK_WAITBLOCK First, Last;
if (InterlockedBitTestAndSetPointer(&SRWLock->Ptr,
RTL_SRWLOCK_OWNED_BIT))
{
LONG_PTR CurrentValue, NewValue;
while (1)
{
CurrentValue = *(volatile LONG_PTR *)&SRWLock->Ptr;
if (CurrentValue & RTL_SRWLOCK_SHARED)
{
/* A shared lock is being held right now. We need to add a wait block! */
if (CurrentValue & RTL_SRWLOCK_CONTENDED)
{
goto AddWaitBlock;
}
else
{
/* There are no wait blocks so far, we need to add ourselves as the first
wait block. We need to keep the shared count! */
StackWaitBlock.Exclusive = TRUE;
StackWaitBlock.SharedCount = (LONG)(CurrentValue >> RTL_SRWLOCK_BITS);
StackWaitBlock.Next = NULL;
StackWaitBlock.Last = &StackWaitBlock;
StackWaitBlock.Wake = 0;
ASSERT_SRW_WAITBLOCK(&StackWaitBlock);
NewValue = (ULONG_PTR)&StackWaitBlock | RTL_SRWLOCK_SHARED | RTL_SRWLOCK_CONTENDED | RTL_SRWLOCK_OWNED;
if ((LONG_PTR)InterlockedCompareExchangePointer(&SRWLock->Ptr,
(PVOID)NewValue,
(PVOID)CurrentValue) == CurrentValue)
{
RtlpAcquireSRWLockExclusiveWait(SRWLock,
&StackWaitBlock);
/* Successfully acquired the exclusive lock */
break;
}
}
}
else
{
if (CurrentValue & RTL_SRWLOCK_OWNED)
{
/* An exclusive lock is being held right now. We need to add a wait block! */
if (CurrentValue & RTL_SRWLOCK_CONTENDED)
{
AddWaitBlock:
StackWaitBlock.Exclusive = TRUE;
StackWaitBlock.SharedCount = 0;
StackWaitBlock.Next = NULL;
StackWaitBlock.Last = &StackWaitBlock;
StackWaitBlock.Wake = 0;
ASSERT_SRW_WAITBLOCK(&StackWaitBlock);
First = RtlpAcquireWaitBlockLock(SRWLock);
if (First != NULL)
{
Last = First->Last;
Last->Next = &StackWaitBlock;
First->Last = &StackWaitBlock;
RtlpReleaseWaitBlockLock(SRWLock);
RtlpAcquireSRWLockExclusiveWait(SRWLock,
&StackWaitBlock);
/* Successfully acquired the exclusive lock */
break;
}
}
else
{
/* There are no wait blocks so far, we need to add ourselves as the first
wait block. We need to keep the shared count! */
StackWaitBlock.Exclusive = TRUE;
StackWaitBlock.SharedCount = 0;
StackWaitBlock.Next = NULL;
StackWaitBlock.Last = &StackWaitBlock;
StackWaitBlock.Wake = 0;
ASSERT_SRW_WAITBLOCK(&StackWaitBlock);
NewValue = (ULONG_PTR)&StackWaitBlock | RTL_SRWLOCK_OWNED | RTL_SRWLOCK_CONTENDED;
if ((LONG_PTR)InterlockedCompareExchangePointer(&SRWLock->Ptr,
(PVOID)NewValue,
(PVOID)CurrentValue) == CurrentValue)
{
RtlpAcquireSRWLockExclusiveWait(SRWLock,
&StackWaitBlock);
/* Successfully acquired the exclusive lock */
break;
}
}
}
else
{
if (!InterlockedBitTestAndSetPointer(&SRWLock->Ptr,
RTL_SRWLOCK_OWNED_BIT))
{
/* We managed to get hold of a simple exclusive lock! */
break;
}
}
}
YieldProcessor();
}
}
}
VOID
NTAPI
RtlReleaseSRWLockExclusive(IN OUT PRTL_SRWLOCK SRWLock)
{
LONG_PTR CurrentValue, NewValue;
PRTLP_SRWLOCK_WAITBLOCK WaitBlock;
while (1)
{
CurrentValue = *(volatile LONG_PTR *)&SRWLock->Ptr;
if (!(CurrentValue & RTL_SRWLOCK_OWNED))
{
RtlRaiseStatus(STATUS_RESOURCE_NOT_OWNED);
}
if (!(CurrentValue & RTL_SRWLOCK_SHARED))
{
if (CurrentValue & RTL_SRWLOCK_CONTENDED)
{
/* There's a wait block, we need to wake the next pending
acquirer (exclusive or shared) */
WaitBlock = RtlpAcquireWaitBlockLock(SRWLock);
if (WaitBlock != NULL)
{
RtlpReleaseWaitBlockLockExclusive(SRWLock,
WaitBlock);
/* We released the lock */
break;
}
}
else
{
/* This is a fast path, we can simply clear the RTL_SRWLOCK_OWNED
bit. All other bits should be 0 now because this is a simple
exclusive lock and no one is waiting. */
ASSERT(!(CurrentValue & ~RTL_SRWLOCK_OWNED));
NewValue = 0;
if ((LONG_PTR)InterlockedCompareExchangePointer(&SRWLock->Ptr,
(PVOID)NewValue,
(PVOID)CurrentValue) == CurrentValue)
{
/* We released the lock */
break;
}
}
}
else
{
/* The RTL_SRWLOCK_SHARED bit must not be present now,
not even in the contended case! */
RtlRaiseStatus(STATUS_RESOURCE_NOT_OWNED);
}
YieldProcessor();
}
}
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