Author: Uri Blass
Date: 11:40:25 08/30/04
Go up one level in this thread
On August 30, 2004 at 13:57:59, Robert Hyatt wrote:
>On August 30, 2004 at 11:25:26, Alessandro Scotti wrote:
>
>>On August 30, 2004 at 10:20:05, Robert Hyatt wrote:
>>
>>>What do you do about the case where you type "command"<CR> "command"<CR> (two
>>>commands) before your program does the "check for input"? You do the first
>>>fgets() and the C library sucks both commands into its internal buffer, by
>>>reading the data from the O/S, and it gives you the first command. Now when you
>>>ask "is there more input" you are asking the O/S and it says "no" even though
>>>the C library has the second command in its buffer. This is a _common_ problem
>>>when people first modify their engines to run with winboard/xboard. It is such
>>>a problem that Tim and I wrote a lot of text to explain why this is a problem
>>>and how to get around it...
>>
>>Well I don't know because I've never found this problem in any of my prototypes.
>>Maybe it's the mix of asking both the O/S and the standard lib that messes
>>things up.
>>I have a separate thread that performs fgets (I also tried fread and ReadFile
>>and they work as well) and simply blocks if there is nothing to get. I have just
>>tried the experiment you suggested and it works fine, probably because I always
>>use fgets() so I'm reading from the same buffer.
>
>
>The problem is that the question "is there input to read" polls the operating
>system, not the library buffer. That's why all the warnings and explanations
>are in the engine interface document that comes with xboard/winboard.
>
>The only solutions are (a) threads; (b) non-buffered I/O. Either works.
>Threads cause a few more portability issues.
I do not use threads and use fget and Movei could play many games with no
problem(the only problem is that I cannot check often for getting input during
pondering like crafty unless I want to do the program significantly slower).
I use input_available function(I post the function later in this message) to
find if there is an input during pondering and if there is an input I use fget
to get the command and if the command is time command I wait passively for
winboard command by fget.
I assume that winboard will send me a move immediately after time command.
int input_available(void)
{
DWORD nchars;
/* When using Standard C input functions, also check if there
is anything in the buffer. After a call to such functions,
the input waiting in the pipe will be copied to the buffer,
and the call to PeekNamedPipe can indicate no input available.
Setting stdin to unbuffered was not enough, IIRC */
//input_init();
if (stdin->_cnt > 0)
return 1;
if (is_pipe)
{
/* When running under a GUI, you will end here. */
if (!PeekNamedPipe(input_handle, NULL, 0, NULL, &nchars, NULL))
return 1;
/* Something went wrong. Probably the parent program exited.
Could call exit() here. Returning 1 will make the next call
to the input function return EOF, where this should be
catched then. */
return nchars != 0;
}
else
if (nodes&Nodes_Frequency)
return 0;
else
return _kbhit(); /* In "text-mode" without GUI */
}
if (nodes&Nodes_Frequency) was added because I thought to use
input_available at every node(similiar to crafty that seems to check if the
search was interupted almost every node and not every nodes_frequency nodes.
Unfortunately I found that if I call input_available in every node under
winboard it is very expensive when if I call input_available in every node under
text mode it is not expensive.
Uri
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