%
% (c) The AQUA Project, Glasgow University, 1995
%
%************************************************************************
%*                                                                      *
\section[Select.lc]{Select Available File Descriptors}
%*									*
%************************************************************************

\begin{code}

#ifdef CONCURRENT

/* #define STK_CHK_DEBUG */

#define NULL_REG_MAP
#define NON_POSIX_SOURCE
/* Should there be a POSIX alternative based on poll()? */
#include "stgdefs.h"

# if defined(HAVE_SYS_TYPES_H)
#  include <sys/types.h>
# endif

# ifdef HAVE_SYS_TIME_H
#  include <sys/time.h>
# endif

void
AwaitEvent(I_ delta)
{
    P_ tso, prev, next;
    rtsBool ready;
    fd_set rfd;
    I_ us;
    I_ min;
    I_ maxfd=0;
    struct timeval tv;

    min = delta == 0 ? 0x7fffffff : 0;

    /* 
     * Collect all of the fd's that we're interested in, and capture
     * the minimum waiting time for the delayed threads.
     *
     * (I_)TSO_EVENT(tso) < 0 => thread waiting on fd (-(I_)TSO_EVENT(tso))
     *
     */
    FD_ZERO(&rfd);
    for(tso = WaitingThreadsHd; tso != Nil_closure; tso = TSO_LINK(tso)) {
	us = (I_) TSO_EVENT(tso);
	if (us > 0) {
	    /* Looking at a delay event */
	    if (us < min)
		min = us;
	} else {
	    /* Looking at a wait event */
	    maxfd = ((-us)> maxfd) ? (-us) : maxfd;
	    FD_SET((-us), &rfd);
	}
    }

    /* Check for any interesting events */

    tv.tv_sec = min / 1000000;
    tv.tv_usec = min % 1000000;

    while (select((maxfd==0 ? 0 : (maxfd+1)), &rfd, NULL, NULL, &tv) < 0) {
	if (errno != EINTR) {
	    fflush(stdout);
	    fprintf(stderr, "AwaitEvent: select failed\n");
	    EXIT(EXIT_FAILURE);
	}
    }	
 
    if (delta == 0)
	delta=min;

    prev = NULL;
    for(tso = WaitingThreadsHd; tso != Nil_closure; tso = next) {
	next = TSO_LINK(tso);
	us = (I_) TSO_EVENT(tso);
	if (us > 0) {
	    /* Looking at a delay event */
	    us -= delta;
	    ready = (us <= 0);
	    if (!ready)
		TSO_EVENT(tso) = (W_) us;
	} else {
	    /* Looking at a wait event */
	    ready = FD_ISSET((-us), &rfd);
	}
	if (ready) {

#if defined(GRAN)
            if (ThreadQueueTl == Nil_closure)
		ThreadQueueHd = tso;
            else
		TSO_LINK(ThreadQueueTl) = tso;
	    ThreadQueueTl = tso;
	    TSO_LINK(tso) = Nil_closure;
#else
            if (RunnableThreadsTl == Nil_closure)
		RunnableThreadsHd = tso;
            else
		TSO_LINK(RunnableThreadsTl) = tso;
	    RunnableThreadsTl = tso;
	    TSO_LINK(tso) = Nil_closure;
#endif
	} else {
	    if (prev == NULL)
		WaitingThreadsHd = tso;
	    else
		TSO_LINK(prev) = tso;
	    prev = tso;
	}
    }
    if (prev == NULL)
	WaitingThreadsHd = WaitingThreadsTl = Nil_closure;
    else {
	TSO_LINK(prev) = Nil_closure;
	WaitingThreadsTl = prev;
    }
}

#endif /* CONCURRENT */
\end{code}