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From: tholm@uvicctr.UUCP (Terrence W. Holm)
Newsgroups: comp.os.minix
Subject: POSIX sleep(3)
Message-ID: <527@uvicctr.UUCP>
Date: 25 Oct 88 20:39:49 GMT
Reply-To: tholm@uvicctr.UUCP (Terrence W. Holm)
Organization: University of Victoria, Victoria B.C. Canada
Lines: 99

EFTH MINIX report #51  - October 1988 -  POSIX sleep(3)


The MINIX 1.3 sleep(3) does not handle alarm(2) pending
when sleep(3) is called. Nor does it return a correct
value. The following corrects these problems.

----------------------------------------------------------
echo x - sleep.3
gres '^X' '' > sleep.3 << '/'
XSUBROUTINES
X    sleep(3)		- suspend execution for awhile
X
XINVOCATION
X    unsigned sleep( secs )
X      unsigned secs;
X
XEXPLANATION
X    The process halts execution for <secs> seconds. It
X    will wake up early if any non-ignored signal occurs.
X
X    If an alarm(2) was already set then sleep(3) uses
X    the minimum of the time remaining and <secs> as the
X    sleep time. If the alarm(2) signal expires first, then
X    its handler is called and sleep(3) returns.
X
X    If an alarm(2) is still pending after sleep(3) completes,
X    then its time is adjusted by how long the process
X    really slept.
X
XRESULTS
X    Returns the number of seconds remaining until <secs>
X    should occur. This is non-zero when another signal woke
X    up sleep(3) early.
X
XREFERENCES
X    alarm(2), kill(2), pause(2), signal(2)
/
echo x - sleep.c
gres '^X' '' > sleep.c << '/'
X/*  sleep(3)
X *
X *  Sleep(n) pauses for 'n' seconds by scheduling an alarm interrupt.
X *
X *  Changed to conform with POSIX      Terrence W. Holm      Oct. 1988
X */
X
X#include <signal.h>
X
X
Xstatic _alfun()	/* Used with sleep() below */
X  {
X  }
X
X
Xunsigned sleep( secs )
X  unsigned secs;
X
X  {
X  unsigned current_secs;
X  unsigned remaining_secs;
X  void     (*old_signal)();
X
X  if ( secs == 0 )
X    return( 0 );
X
X  current_secs = alarm( 0 );   /*  Is there currently an alarm?  */
X
X  if ( current_secs == 0  ||  current_secs > secs )
X    {
X    old_signal = signal( SIGALRM, _alfun );
X
X    alarm( secs );
X    pause();
X    remaining_secs = alarm( 0 );
X
X    signal( SIGALRM, old_signal );
X
X    if ( current_secs > secs )
X	alarm( current_secs - ( secs - remaining_secs ) );
X
X    return( remaining_secs );
X    }
X
X
X  /*  current_secs <= secs,  ie. alarm should occur before secs  */
X
X  alarm( current_secs );
X  pause();
X  remaining_secs = alarm( 0 );
X
X  alarm( remaining_secs );
X
X  return( secs - ( current_secs - remaining_secs ) );
X  }
/
----------------------------------------------------------

		Terrence W. Holm
		  uw-beaver!uvicctr!tholm