From: "Mauricio Fernández" <batsman.geo@...>
Date: 2002-11-13T04:06:22+09:00
Subject: Re: Threading in I/O libraries

On Tue, Nov 12, 2002 at 08:11:31PM +0900, Brian Candler wrote:
> On Tue, Nov 12, 2002 at 04:21:03AM +0900, Yohanes Santoso wrote:
> > > I'd like to ask: how integrated is threading in Ruby's I/O libraries?
> > > 
> > > In particular,
> > > 
> > > (1) if I do a read from a socket, will Ruby call select() first to ensure
> > > that there is data available (to prevent blocking), or do I have to do that
> > > myself?
> > 
> > Determine existence of data by yourself to prevent blocking on that thread.
> 
> That's not quite what I meant. It doesn't matter if that one thread blocks -
> that's actually what I want.
> 
> However, if IO#read simply called the Unix read() function, then the entire
> Ruby interpreter would be locked out (including all other threads).
> 
> So what I was asking is, does IO#read actually do something else? For
> example a kernel#select followed by a read? Then, does the same apply to all
> the I/O functions, like sysread for example?

Use the source, Luke! :)

io.c
************
static long
io_fread(ptr, len, f)
    char *ptr;
    long len;
    FILE *f;
{
    long n = len;
    int c;

    while (n > 0) {
#ifdef READ_DATA_PENDING_COUNT
        int i = READ_DATA_PENDING_COUNT(f);
        if (i <= 0) {
            rb_thread_wait_fd(fileno(f));
            i = READ_DATA_PENDING_COUNT(f);
        }
        if (i > 0) {
            if (i > n) i = n;
            TRAP_BEG;
            c = fread(ptr, 1, i, f);
            TRAP_END;
            if (c < 0) goto eof;
            ptr += c;
            n -= c;
            if (c < i) goto eof;
            continue;
        }
#else
        if (!READ_DATA_PENDING(f)) {
            rb_thread_wait_fd(fileno(f));
        }
#endif

************

Seems Ruby does The Right Thing.
 
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