[PATCH v2 4/8] ntoskrnl.exe: Implement ExAcquireSharedStarveExclusive().

[Zebediah Figura]

Signed-off-by: Zebediah Figura <z.figura12 at gmail.com>
---
 dlls/ntoskrnl.exe/ntoskrnl.exe.spec |  2 +-
 dlls/ntoskrnl.exe/sync.c            | 64 +++++++++++++++++++++++++++++
 include/ddk/wdm.h                   |  1 +
 3 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/dlls/ntoskrnl.exe/ntoskrnl.exe.spec b/dlls/ntoskrnl.exe/ntoskrnl.exe.spec
index 177800a8dc..347febb63f 100644
--- a/dlls/ntoskrnl.exe/ntoskrnl.exe.spec
+++ b/dlls/ntoskrnl.exe/ntoskrnl.exe.spec
@@ -122,7 +122,7 @@
 @ stub DbgSetDebugFilterState
 @ stdcall ExAcquireResourceExclusiveLite(ptr long)
 @ stdcall ExAcquireResourceSharedLite(ptr long)
-@ stub ExAcquireSharedStarveExclusive
+@ stdcall ExAcquireSharedStarveExclusive(ptr long)
 @ stub ExAcquireSharedWaitForExclusive
 @ stub ExAllocateFromPagedLookasideList
 @ stdcall ExAllocatePool(long long)
diff --git a/dlls/ntoskrnl.exe/sync.c b/dlls/ntoskrnl.exe/sync.c
index 82667e8510..2b362efc82 100644
--- a/dlls/ntoskrnl.exe/sync.c
+++ b/dlls/ntoskrnl.exe/sync.c
@@ -880,3 +880,67 @@ BOOLEAN WINAPI ExAcquireResourceSharedLite( ERESOURCE *resource, BOOLEAN wait )
 
     return TRUE;
 }
+
+/***********************************************************************
+ *           ExAcquireSharedStarveExclusive  (NTOSKRNL.EXE.@)
+ */
+BOOLEAN WINAPI ExAcquireSharedStarveExclusive( ERESOURCE *resource, BOOLEAN wait )
+{
+    OWNER_ENTRY *entry;
+    KIRQL irql;
+
+    TRACE("resource %p, wait %u.\n", resource, wait);
+
+    KeAcquireSpinLock( &resource->SpinLock, &irql );
+
+    entry = resource_get_shared_entry( resource, (ERESOURCE_THREAD)KeGetCurrentThread() );
+
+    if (resource->Flag & ResourceOwnedExclusive)
+    {
+        if (resource->OwnerEntry.OwnerThread == (ERESOURCE_THREAD)KeGetCurrentThread())
+        {
+            resource->ActiveEntries++;
+            KeReleaseSpinLock( &resource->SpinLock, irql );
+            return TRUE;
+        }
+    }
+    /* We are starving exclusive waiters, but we cannot steal the resource out
+     * from under an exclusive waiter who is about to acquire it. (Because of
+     * locking, and because exclusive waiters are always waked first, this is
+     * guaranteed to be the case if the resource is unowned and there are
+     * exclusive waiters.) */
+    else if (!(!resource->ActiveEntries && resource->NumberOfExclusiveWaiters))
+    {
+        entry->OwnerCount++;
+        resource->ActiveEntries++;
+        KeReleaseSpinLock( &resource->SpinLock, irql );
+        return TRUE;
+    }
+
+    if (!wait)
+    {
+        KeReleaseSpinLock( &resource->SpinLock, irql );
+        return FALSE;
+    }
+
+    if (!resource->SharedWaiters)
+    {
+        resource->SharedWaiters = heap_alloc( sizeof(*resource->SharedWaiters) );
+        KeInitializeSemaphore( resource->SharedWaiters, 0, INT_MAX );
+    }
+    resource->NumberOfSharedWaiters++;
+
+    KeReleaseSpinLock( &resource->SpinLock, irql );
+
+    KeWaitForSingleObject( resource->SharedWaiters, Executive, KernelMode, FALSE, NULL );
+
+    KeAcquireSpinLock( &resource->SpinLock, &irql );
+
+    entry->OwnerCount++;
+    resource->ActiveEntries++;
+    resource->NumberOfSharedWaiters--;
+
+    KeReleaseSpinLock( &resource->SpinLock, irql );
+
+    return TRUE;
+}
diff --git a/include/ddk/wdm.h b/include/ddk/wdm.h
index a153942bf5..8023fda64e 100644
--- a/include/ddk/wdm.h
+++ b/include/ddk/wdm.h
@@ -1514,6 +1514,7 @@ NTSTATUS  WINAPI DbgQueryDebugFilterState(ULONG, ULONG);
 void      WINAPI ExAcquireFastMutexUnsafe(PFAST_MUTEX);
 BOOLEAN   WINAPI ExAcquireResourceExclusiveLite(ERESOURCE*,BOOLEAN);
 BOOLEAN   WINAPI ExAcquireResourceSharedLite(ERESOURCE*,BOOLEAN);
+BOOLEAN   WINAPI ExAcquireSharedStarveExclusive(ERESOURCE*,BOOLEAN);
 PVOID     WINAPI ExAllocatePool(POOL_TYPE,SIZE_T);
 PVOID     WINAPI ExAllocatePoolWithQuota(POOL_TYPE,SIZE_T);
 PVOID     WINAPI ExAllocatePoolWithTag(POOL_TYPE,SIZE_T,ULONG);
-- 
2.21.0