180 lines
7.7 KiB
C
180 lines
7.7 KiB
C
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/*++
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Copyright (c) 1995 Microsoft Corporation
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Module Name:
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ntos\tdi\isn\fwd\rwlock.h
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Abstract:
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Reader-Writer lock macros
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Author:
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Vadim Eydelman
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Revision History:
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--*/
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#ifndef _IPXFWD_RWLOCK_
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#define _IPXFWD_RWLOCK_
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typedef volatile LONG VOLCTR, *PVOLCTR;
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typedef PVOLCTR RWCOOKIE, *PRWCOOKIE;
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// Reader- writer lock.
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// Allows no-lock access to the tables for readers - they merely
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// increment the counter to record their presence upon entrance
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// and decrement the same counter as they leave.
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// Writers are supposed to be serialized (externally) and their
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// actions are limited to ATOMIC insertions of new elements and
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// ATOMIC removals/replacements. The removals/replacements MUST
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// be followed by a wait for all potential readers who might still
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// be using the element that was removed/replaced
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typedef struct _RW_LOCK {
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KEVENT Event; // Event to release waiting writer
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VOLCTR Ctr1; // Two alternating
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VOLCTR Ctr2; // reader counters
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volatile PVOLCTR CurCtr; // Counter currently in use
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} RW_LOCK, *PRW_LOCK;
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/*++
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*******************************************************************
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I n i t i a l i z e R W L o c k
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Routine Description:
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Initializes RW lock
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Arguments:
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lock - pointer to lock to initialize
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Return Value:
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None
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*******************************************************************
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--*/
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//VOID
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//InitializeRWLock (
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// PRW_LOCK lock
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// );
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#define InitializeRWLock(lock) { \
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KeInitializeEvent (&(lock)->Event, \
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SynchronizationEvent, \
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FALSE); \
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(lock)->Ctr1 = (lock)->Ctr2 = 0; \
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(lock)->CurCtr = &(lock)->Ctr1; \
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}
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/*++
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*******************************************************************
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A c q u i r e R e a d e r A c c e s s
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Routine Description:
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Acquires reader access to resource protected by the lock
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Arguments:
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lock - pointer to lock
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cookie - pointer to buffer to store lock state for subsequent
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release operation
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Return Value:
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None
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*******************************************************************
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--*/
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//VOID
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//AcquireReaderAccess (
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// IN PRW_LOCK lock,
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// OUT RWCOOKIE cookie
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// );
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#define AcquireReaderAccess(lock,cookie) \
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do { \
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register LONG local,local1; \
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cookie = (lock)->CurCtr; /*Get current counter pointer*/ \
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local = *(cookie); /*Copy counter value*/ \
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local1 = local + 1; \
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if ((local>=0) /*If counter is valid*/ \
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/*and it hasn't changed while*/ \
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/*we were checking and trying*/ \
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/*to increment it,*/ \
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&& (InterlockedCompareExchange ( \
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(PLONG)(cookie), \
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local1, \
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local) \
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==local)) \
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break; /*then we obtained the access*/ \
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} while (1) /*otherwise, we have to do it again (possibly with*/\
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/*the other counter if writer switched it on us)*/
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/*++
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*******************************************************************
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R e l e a s e R e a d e r A c c e s s
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Routine Description:
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Releases reader access to resource protected by the lock
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Arguments:
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lock - pointer to lock
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cookie - lock state for subsequent stored during acquire operation
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Return Value:
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None
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*******************************************************************
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--*/
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//VOID
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//ReleaseReaderAccess (
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// IN PRW_LOCK lock,
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// IN RWCOOKIE cookie
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// );
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#define ReleaseReaderAccess(lock,cookie) { \
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/*If counter drops below 0, we have to signal the writer*/ \
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if (InterlockedDecrement((PLONG)cookie)<0) { \
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LONG res; \
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ASSERT (*(cookie)==-1); \
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res = KeSetEvent (&(lock)->Event, 0, FALSE); \
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ASSERT (res==0); \
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} \
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}
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/*++
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*******************************************************************
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W a i t F o r A l l R e a d e r s
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Routine Description:
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Waits for all readers that were accessing the resource prior
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to the call to exit (New readers are not included)
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Arguments:
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lock - pointer to lock
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Return Value:
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None
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*******************************************************************
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--*/
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//VOID
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//WaitForAllReaders (
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// PRW_LOCK lock
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// );
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#define WaitForAllReaders(lock) { \
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RWCOOKIE prevCtr = (lock)->CurCtr; \
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/*Switch the counter first*/ \
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if (prevCtr==&(lock)->Ctr1) { \
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(lock)->Ctr2 = 0; \
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(lock)->CurCtr = &(lock)->Ctr2; \
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} \
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else { \
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ASSERT (prevCtr==&(lock)->Ctr2); \
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(lock)->Ctr1 = 0; \
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(lock)->CurCtr = &(lock)->Ctr1; \
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} \
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/* If not all readers are gone, we'll have to wait for them*/ \
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if (InterlockedDecrement((PLONG)prevCtr)>=0) { \
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NTSTATUS status \
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= KeWaitForSingleObject ( \
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&(lock)->Event, \
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Executive, \
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ExGetPreviousMode(),\
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FALSE, \
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0); \
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ASSERT (NT_SUCCESS(status)); \
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ASSERT (*prevCtr==-1); \
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} \
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}
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#endif
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