RtlRunOnceBeginInitialize - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers 
#ifndef _NTRTL_H
#if (PHNT_VERSION >= PHNT_VISTA)

_Must_inspect_result_
NTSYSAPI
NTSTATUS
NTAPI
RtlRunOnceBeginInitialize(
    _Inout_ PRTL_RUN_ONCE RunOnce,
    _In_ ULONG Flags,
    _Outptr_opt_result_maybenull_ PVOID *Context
    );

#endif
#endif

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This function is documented in Windows Driver Kit.

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