Re: [clisp-list] read-char-no-hang-p hangs on com port

[Vladimir T. <vtz...@gm...>]

On 9/29/09, Angel Popov <ang...@ya...> wrote:
> Thanks for the advise,
>
> Here is the debug session, but still cannot figure out what is going on.
> Found an article that could be related
> http://msdn.microsoft.com/en-us/library/ms687032(VS.85).aspx - It could be
> something with ENABLE_LINE_INPUT console mode.
>
> the lisp program is
>
> (defvar com (open "COM1" :direction :io))
> (print (read-char-will-hang-p com))
>
> The trace session:
>
> Breakpoint 1, fd_read_wont_hang_p (fd=0x73c) at ../src/win32aux.d:449
> 449       switch (GetFileType(fd)) {
> 1: fd = (HANDLE) 0x73c
> (gdb) s
> 453             if (GetNumberOfConsoleInputEvents(fd,&nevents)) { /* It's a
> console. */
> 1: fd = (HANDLE) 0x73c
> (gdb) n
> 489             } else if (!(GetLastError()==ERROR_INVALID_HANDLE)) {
> 1: fd = (HANDLE) 0x73c
> (gdb) n
> 494           switch (WaitForSingleObject(fd,0)) {
> 1: fd = (HANDLE) 0x73c
> (gdb) s
> 496               return 1;

WaitForSingleObject cannot be used on serial port handles -
http://msdn.microsoft.com/en-us/library/ms687032(VS.85).aspx. Notice
that files and serial ports are not in the list - wondering why it
does not return an error?

For checking whether there are characters to be read -
ClearCommError() may be used
(http://msdn.microsoft.com/en-us/library/aa363180(VS.85).aspx). In
order to use it we should have explicit knowledge that this is serial
port handle or just try it an handle the error in case it's not
(probably ERROR_INVALID_HANDLE).

Sam?