Since pevents is supposed to be a WFMO clone, I'm not sure if this is a bug report or a feature request, because the implementation just doesn't do this right now.

From the Remarks section of the documentation for WaitForMultipleObjects on MSDN (emphasis mine):

When bWaitAll is TRUE, the function's wait operation is completed only when the states of all objects have been set to signaled. The function does not modify the states of the specified objects until the states of all objects have been set to signaled. For example, a mutex can be signaled, but the thread does not get ownership until the states of the other objects are also set to signaled. In the meantime, some other thread may get ownership of the mutex, thereby setting its state to nonsignaled.

This means that during a WFME call where waitAll = true, the state of events shall not be reset, in the specific case of auto-reset Events, until all are simultaneously in the set state. This would apply to manual-reset Events too, except that their state cannot change due to a WaitForEvent/WFME call unless an explicit call to ResetEvent is made. Note that even though WMFE( waitAll = true, milliseconds = UINT64_MAX ) shall return only if all events are signaled, this bug applies to waitAll = true calls to WFME with any timeout value because the state shall only change once all events are in the set state, and the current implementation immediately resets the event before waiting if the Event is set.

This seems to be a significant change (hence, a feature request?) simply because the wait state is never added to any Event that is already in the set state, which is incorrect because another thread could call ResetEvent on any already-set Event, change the state back to not-set, and thus should increment the EventsLeft shared state member.

The following test case exhibits the error:

neosmart::neosmart_event_t lEvents[3];
lEvents[0] = neosmart::CreateEvent( false, true );  // Already Signaled AutoReset
lEvents[1] = neosmart::CreateEvent( false, false ); // Not Signaled AutoReset
lEvents[2] = neosmart::CreateEvent( false, true );  // Already Signaled AutoReset

// WFMO is non-destructive if a wait-all with any timeout value fails on auto-reset events.
if ( neosmart::WaitForMultipleEvents( lEvents, 3, TRUE, 0 ) == WAIT_OBJECT_0 )
    throw std::runtime_error( "Must not be signaled!" );

// FAILS!!
if ( neosmart::WaitForEvent( lEvents[0], 0 ) != WAIT_OBJECT_0 )
    throw std::runtime_error( "Must be signaled" );

if ( neosmart::WaitForEvent( lEvents[1], 0 ) != WAIT_TIMEOUT )
    throw std::runtime_error( "Must not be signaled" );

// FAILS!!
if ( neosmart::WaitForEvent( lEvents[2], 0 ) != WAIT_OBJECT_0 )
    throw std::runtime_error( "Must be signaled" );


// WFMO is destructive if a wait-all succeeds with any timeout value on auto-reset events.
for ( auto& lEvent : lEvents )
    neosmart::SetEvent( lEvent );
if ( neosmart::WaitForMultipleEvents( lEvents, 3, TRUE, 0 ) != WAIT_OBJECT_0 )  // OK
    throw std::runtime_error( "Must be signaled!" );
for ( auto& lEvent : lEvents )
{
    if ( neosmart::WaitForEvent( lEvent, 0 ) != WAIT_TIMEOUT ) // OK
        throw std::runtime_error( "Must not be signaled" );
    neosmart::DestroyEvent( lEvent );
}