In the case of c# (NdisApiDemo), the CPU usage is high when the program is compi

The high CPU usage is likely due to the fact that the packet event is never reset. This causes the thread to continuously poll the driver without pausing.

Solution:
You need to reset the AutoResetEvent or ManualResetEvent in waitHandlesManualResetEvents after processing packets. This ensures the thread properly waits for new packets instead of running in a tight loop.

Fixed Code:

private static unsafe void PassThruUnsortedThread
(
    NdisApi filter,
    WaitHandle[] waitHandles,
    IReadOnlyList<AutoResetEvent> waitHandlesManualResetEvents)
{
    const int bufferSize = 32;
    var buffers = new IntPtr[bufferSize];

    for (int i = 0; i < buffers.Length; i++)
    {
        buffers[i] = (IntPtr)filter.CreateIntermediateBuffer();
    }

    while (true)
    {
        int eventIndex = WaitHandle.WaitAny(waitHandles);  // Wait for an event to be signaled

        uint packetsSuccess = 0;

        while (filter.ReadPacketsUnsorted(buffers, bufferSize, ref packetsSuccess))
        {
            for (int i = 0; i < packetsSuccess; i++)
            {
                EthernetPacket ethPacket = buffers[i].GetEthernetPacket(filter);
                if (ethPacket.PayloadPacket is IPv4Packet iPv4Packet)
                {
                    if (iPv4Packet.PayloadPacket is TcpPacket tcpPacket)
                    {
                        // Console.WriteLine($”{iPv4Packet.SourceAddress}:{tcpPacket.SourcePort} -> {iPv4Packet.DestinationAddress}:{tcpPacket.DestinationPort}.”);
                    }
                }
            }

            if (packetsSuccess > 0)
            {
                filter.SendPacketsUnsorted(buffers, packetsSuccess, out uint numPacketsSuccess);
            }
        }

        // Reset the event to allow proper waiting
        if (eventIndex >= 0 && eventIndex < waitHandlesManualResetEvents.Count)
        {
            waitHandlesManualResetEvents[eventIndex].Reset();
        }
    }
}

Explanation:

• Wait for an event: WaitHandle.WaitAny(waitHandles); ensures the thread only runs when a packet event is signaled.
• Process packets normally: The loop reads packets, processes them, and sends them back.
• Reset the event: After processing packets, waitHandlesManualResetEvents[eventIndex].Reset(); is called to prevent continuous polling.

This should significantly reduce CPU usage.

Thank you for pointing that out. I made an incorrect assumption about the parameters, but I believe you understood the main idea correctly—when there are no packets to read, the packet events should be reset, and the thread should wait on them. I appreciate the clarification!