#ifndef _NTEXAPI_H
#if (PHNT_MODE != PHNT_MODE_KERNEL)

/**
 * The NtReleaseMutant routine releases ownership of a mutant object.
 *
 * \param MutantHandle A handle to the mutant object.
 * \param PreviousCount A pointer to a variable that receives the previous count of the mutant object.
 * \return NTSTATUS Successful or errant status.
 */
NTSYSCALLAPI
NTSTATUS
NTAPI
NtReleaseMutant(
    _In_ HANDLE MutantHandle,
    _Out_opt_ PLONG PreviousCount
    );

#endif
#endif
View code on GitHub

#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwReleaseMutant(
    _In_ HANDLE MutantHandle,
    _Out_opt_ PLONG PreviousCount
    );

#endif
View code on GitHub