Implemented NtYieldExecution.

dlls/kernel/kernel_main.c

@@ -241,17 +241,6 @@ LONG WINAPI KERNEL_nop(void)
     return 0;
 }
 
-/***********************************************************************
- *		SwitchToThread (KERNEL32.@)
- */
-
-BOOL WINAPI SwitchToThread(void)
-{
-    Sleep(0);
-    return 1;
-}
-
-
 /***********************************************************************
  *           MulDiv   (KERNEL32.@)
  * RETURNS

dlls/kernel/sync.c

@@ -91,6 +91,15 @@ DWORD WINAPI SleepEx( DWORD timeout, BOOL alertable )
 }
 
 
+/***********************************************************************
+ *		SwitchToThread (KERNEL32.@)
+ */
+BOOL WINAPI SwitchToThread(void)
+{
+    return (NtYieldExecution() != STATUS_NO_YIELD_PERFORMED);
+}
+
+
 /***********************************************************************
  *           WaitForSingleObject   (KERNEL32.@)
  */

dlls/ntdll/ntdll.spec

@@ -270,6 +270,7 @@
 @ stdcall NtWriteFile(long long ptr ptr ptr ptr long ptr ptr)
 @ stub NtWriteRequestData
 @ stdcall NtWriteVirtualMemory(long ptr ptr long ptr)
+@ stdcall NtYieldExecution()
 @ stub PfxFindPrefix
 @ stub PfxInitialize
 @ stub PfxInsertPrefix
@@ -1079,7 +1080,6 @@
 @ stub NtReadFileScatter
 @ stub NtSignalAndWaitForSingleObject
 @ stub NtWriteFileGather
-@ stub NtYieldExecution
 @ stub RtlAddAtomToAtomTable
 @ stub RtlAllocateHandle
 @ stub RtlCreateAtomTable

dlls/ntdll/sync.c

@@ -618,6 +618,20 @@ NTSTATUS WINAPI NtWaitForSingleObject(HANDLE handle, BOOLEAN alertable, const LA
 }
 
 
+/******************************************************************
+ *		NtYieldExecution (NTDLL.@)
+ */
+NTSTATUS WINAPI NtYieldExecution(void)
+{
+#ifdef HAVE_SCHED_YIELD
+    sched_yield();
+    return STATUS_SUCCESS;
+#else
+    return STATUS_NO_YIELD_PERFORMED;
+#endif
+}
+
+
 /******************************************************************
  *		NtDelayExecution (NTDLL.@)
  */
@@ -635,9 +649,10 @@ NTSTATUS WINAPI NtDelayExecution( BOOLEAN alertable, const LARGE_INTEGER *timeou
     {
         for (;;) select( 0, NULL, NULL, NULL, NULL );
     }
-#ifdef HAVE_SCHED_YIELD
-    else if (!timeout->QuadPart) sched_yield();
-#endif
+    else if (!timeout->QuadPart)
+    {
+        NtYieldExecution();
+    }
     else
     {
         abs_time_t when;

include/winternl.h

@@ -1371,6 +1371,7 @@ NTSTATUS  WINAPI NtWaitForSingleObject(HANDLE,BOOLEAN,const LARGE_INTEGER*);
 NTSTATUS  WINAPI NtWaitForMultipleObjects(ULONG,const HANDLE*,BOOLEAN,BOOLEAN,const LARGE_INTEGER*);
 NTSTATUS  WINAPI NtWriteFile(HANDLE,HANDLE,PIO_APC_ROUTINE,PVOID,PIO_STATUS_BLOCK,const void*,ULONG,PLARGE_INTEGER,PULONG);
 NTSTATUS  WINAPI NtWriteVirtualMemory(HANDLE,void*,const void*,SIZE_T,SIZE_T*);
+NTSTATUS  WINAPI NtYieldExecution(void);
 
 void      WINAPI RtlAcquirePebLock(void);
 BYTE      WINAPI RtlAcquireResourceExclusive(LPRTL_RWLOCK,BYTE);