Hello Donn, Friday, February 10, 2006, 12:47:42 AM, you wrote:
DC> "Slow" devices like pipes, sockets etc. get along fine with Handles DC> or whatever buffered I/O - as long as you have only one going at a time. DC> Multiple input sources - like, say you want to read a process' output DC> (unit 1) and diagnostic output (unit 2) separately, and either one has DC> the potential to fill up the pipe and block while you're waiting for DC> input on the other pipe - buffers at least complicate the dispatching DC> mechanics you need for this, if not make it impossible.
are you tried LineBuffering and NoBuffering? seem that it is developed exactly for this case (plus for terminals)
DC> That's part of the idea, it helps keep the data out of buffers where DC> select or whatever can't see it. DC> But then you need functions with semantics that really support unbuffered DC> I/O. When select tells you that the device is readable, you don't know DC> that there is one full line, or how many bytes there are, so hGetLine DC> doesn't apply here, nor would the Haskell equivalent of fread(3) if there DC> were one. The only thing left is hGetChar - one char, then select, then DC> another. (And multi-byte chars cause us to worry about this.) when i think how to implementat LineBuffering, i decided that it is the only possible way - read byte a time and see for a '\n'. i don't know how System.IO implemented but i think that it should do the same DC> Since POSIX read(2) already supports exactly the functions you need for DC> unbuffered I/O, it's simpler, easier and more efficient to leave the whole DC> business right there at the file descriptor level. can you please describe that read(2) does that is better than reading char-at-a-time? DC> I'm sure you can make DC> a non-buffering buffer layer work on top of the file descriptor, but what DC> makes it worth the trouble? if you don't have I/O library that implements what you need, it is indeed simpler to use lower I/O directly. if you have I/O library that does that you need, it is easier to write: (hIn, hOut) <- createUnixPipe vPutStrLn hOut "hello" s <- vGetLine hIn i'm writing such lib now, so i'm interested to know what i need to do so that it will work ok. -- Best regards, Bulat mailto:bulatz@HotPOP.com