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[WIN32K]

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Fix buggy mechanism of pushing and popping free gdi handle slots. The old mechanism unneccessarily locked the entry and it was prone to the ABA problem as it didn't use a sequence number.

svn path=/trunk/; revision=50604
This commit is contained in:
Timo Kreuzer 2011-02-03 19:25:09 +00:00
parent 81b68c76fc
commit 66cff693af
1 changed files with 38 additions and 43 deletions
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81
reactos/subsystems/win32/win32k/objects/gdiobj.c
View file

@ -272,64 +272,51 @@ ULONG
FASTCALL
InterlockedPopFreeEntry(VOID)
{
ULONG idxFirst, idxNext, idxPrev;
ULONG iFirst, iNext, iPrev;
PGDI_TABLE_ENTRY pEntry;
DWORD PrevProcId;
DPRINT("Enter InterLockedPopFreeEntry\n");
while (TRUE)
do
{
idxFirst = GdiHandleTable->FirstFree;
/* Get the index and sequence number of the first free entry */
iFirst = GdiHandleTable->FirstFree;
if (!idxFirst)
/* Check if we have a free entry */
if (!(iFirst & GDI_HANDLE_INDEX_MASK))
{
/* Increment FirstUnused and get the new index */
idxFirst = InterlockedIncrement((LONG*)&GdiHandleTable->FirstUnused) - 1;
iFirst = InterlockedIncrement((LONG*)&GdiHandleTable->FirstUnused) - 1;
/* Check if we have entries left */
if (idxFirst >= GDI_HANDLE_COUNT)
/* Check if we have unused entries left */
if (iFirst >= GDI_HANDLE_COUNT)
{
DPRINT1("No more gdi handles left!\n");
return 0;
}
/* Return the old index */
return idxFirst;
return iFirst;
}
/* Get a pointer to the first free entry */
pEntry = GdiHandleTable->Entries + idxFirst;
pEntry = GdiHandleTable->Entries + (iFirst & GDI_HANDLE_INDEX_MASK);
/* Try to lock the entry */
PrevProcId = InterlockedCompareExchange((LONG*)&pEntry->ProcessId, 1, 0);
if (PrevProcId != 0)
{
/* The entry was locked or not free, wait and start over */
DelayExecution();
continue;
}
/* Sanity check: is entry really free? */
ASSERT(((ULONG_PTR)pEntry->KernelData & ~GDI_HANDLE_INDEX_MASK) == 0);
/* Create a new value with an increased sequence number */
iNext = (USHORT)(ULONG_PTR)pEntry->KernelData;
iNext |= (iFirst & ~GDI_HANDLE_INDEX_MASK) + 0x10000;
/* Try to exchange the FirstFree value */
idxNext = (ULONG_PTR)pEntry->KernelData;
idxPrev = InterlockedCompareExchange((LONG*)&GdiHandleTable->FirstFree,
idxNext,
idxFirst);
/* Unlock the free entry */
(void)InterlockedExchange((LONG*)&pEntry->ProcessId, 0);
/* If we succeeded, break out of the loop */
if (idxPrev == idxFirst)
{
break;
}
iPrev = InterlockedCompareExchange((LONG*)&GdiHandleTable->FirstFree,
iNext,
iFirst);
}
while (iPrev != iFirst);
return idxFirst;
/* Sanity check: is entry really free? */
ASSERT(((ULONG_PTR)pEntry->KernelData & ~GDI_HANDLE_INDEX_MASK) == 0);
return iFirst & GDI_HANDLE_INDEX_MASK;
}
/* Pushes an entry of the handle table to the free list,
@ -338,7 +325,7 @@ VOID
FASTCALL
InterlockedPushFreeEntry(ULONG idxToFree)
{
ULONG idxFirstFree, idxPrev;
ULONG iToFree, iFirst, iPrev;
PGDI_TABLE_ENTRY pFreeEntry;
DPRINT("Enter InterlockedPushFreeEntry\n");
@ -346,18 +333,26 @@ InterlockedPushFreeEntry(ULONG idxToFree)
pFreeEntry = GdiHandleTable->Entries + idxToFree;
ASSERT((pFreeEntry->Type & GDI_ENTRY_BASETYPE_MASK) == 0);
ASSERT(pFreeEntry->ProcessId == 0);
pFreeEntry->UserData = NULL;
pFreeEntry->UserData = NULL; // FIXME
ASSERT(pFreeEntry->UserData == NULL);
do
{
idxFirstFree = GdiHandleTable->FirstFree;
pFreeEntry->KernelData = (PVOID)(ULONG_PTR)idxFirstFree;
/* Get the current first free index and sequence number */
iFirst = GdiHandleTable->FirstFree;
idxPrev = InterlockedCompareExchange((LONG*)&GdiHandleTable->FirstFree,
idxToFree,
idxFirstFree);
/* Set the KernelData member to the index of the first free entry */
pFreeEntry->KernelData = UlongToPtr(iFirst & GDI_HANDLE_INDEX_MASK);
/* Combine new index and increased sequence number in iToFree */
iToFree = idxToFree | ((iFirst & ~GDI_HANDLE_INDEX_MASK) + 0x10000);
/* Try to atomically update the first free entry */
iPrev = InterlockedCompareExchange((LONG*)&GdiHandleTable->FirstFree,
iToFree,
iFirst);
}
while (idxPrev != idxFirstFree);
while (iPrev != iFirst);
}