UnixCancellationPipe.cs

using static Vezel.Cathode.Unix.UnixPInvoke;

namespace Vezel.Cathode.Terminals.Unix;

[SuppressMessage("", "CA1001")]
internal sealed class UnixCancellationPipe
{
    private readonly UnixVirtualTerminal _terminal;

    private readonly AnonymousPipeServerStream _server;

    private readonly AnonymousPipeClientStream _client;

    public UnixCancellationPipe(UnixVirtualTerminal terminal)
    {
        _terminal = terminal;
        _server = new(PipeDirection.Out);
        _client = new(PipeDirection.In, _server.ClientSafePipeHandle);
    }

    public unsafe void PollWithCancellation(int handle, CancellationToken cancellationToken)
    {
        // Note that the runtime sets up a SIGPIPE handler for us.

        var unused = false;
        var pipeHandle = _client.SafePipeHandle;

        pipeHandle.DangerousAddRef(ref unused);

        try
        {
            var handles = (stackalloc[] { (int)pipeHandle.DangerousGetHandle(), handle });

            using (var registration = cancellationToken.UnsafeRegister(
                static state => Unsafe.As<UnixCancellationPipe>(state!)._server.WriteByte(42), this))
                if (!_terminal.PollHandles(null, POLLIN, handles))
                    return;

            // Were we canceled?
            if ((handles[0] & POLLIN) != 0)
            {
                // Read the dummy byte that was written to indicate cancellation.
                _ = _client.ReadByte();

                throw new OperationCanceledException(cancellationToken);
            }
        }
        finally
        {
            pipeHandle.DangerousRelease();
        }
    }
}