sleep: guarantee sleeping specified time at minimum (#174)

With this patch, the Korn shell can now guarantee that calls to
sleep on systems using the select or poll method always result in
the system clock advancing by that much time, assuming no
interruptions. This compensates for deficiencies in certain
systems, including SCO UnixWare.

Discussion: https://github.com/ksh93/ksh/pull/174

src/lib/libast/tm/tvsleep.c:
- Ensure that at least the time requested to sleep has elapsed
  for the select and poll methods.
- Simplify the logic of calculating the time remaining to
  sleep and handle the case of an argument of greater than
  10e9 nanoseconds being passed to tvsleep.

src/cmd/ksh93/bltins/sleep.c:
- Eliminate the check for EINTR to handle other cases wherein
  we have not slept enough.

src/cmd/ksh93/tests/variables.sh:
- Improve the diagnostic message when the sleep test fails.
- Revise the SECONDS function test to expect that we always
  sleep for at least the time specified.

src/cmd/ksh93/tests/functions.h:
- Redirect ps stderr to /dev/null. UnixWare ps prints an error
  message about not being able to find the controlling terminal
  when shtests output is piped, but we are only using ps to find
  the PID.

src/cmd/ksh93/bltins/sleep.c

@@ -139,7 +139,7 @@ void sh_delay(double t, int sflag)
 
 	ts.tv_sec = n;
 	ts.tv_nsec = 1000000000 * (t - (double)n);
-	while(tvsleep(&ts, &tx) < 0 && errno == EINTR)
+	while(tvsleep(&ts, &tx) < 0)
 	{
 		if ((shp->trapnote & (SH_SIGSET | SH_SIGTRAP)) || sflag)
 			return;

src/cmd/ksh93/tests/functions.sh

@@ -1126,7 +1126,7 @@ function gosleep
 	"$bin_sleep" 1
 }
 x=$(
-	(sleep .25; pid=; ps | grep sleep | read pid extra; [[ $pid ]] && kill -- "$pid") &
+	(sleep .25; pid=; ps 2>/dev/null | grep sleep | read pid extra; [[ $pid ]] && kill -- "$pid") &
 	gosleep 2> /dev/null
 	print ok
 )

src/cmd/ksh93/tests/variables.sh

@@ -40,11 +40,15 @@ if	(( RANDOM==RANDOM || $RANDOM==$RANDOM ))
 then	err_exit RANDOM variable not working
 fi
 # SECONDS
-let SECONDS=0.0
-sleep .001
-if	(( SECONDS < .001 ))
-then	err_exit "either 'sleep' or \$SECONDS not working"
+float secElapsed=0.0 secSleep=0.001
+let SECONDS=$secElapsed
+sleep $secSleep
+secElapsed=SECONDS
+if	(( secElapsed < secSleep ))
+then	err_exit "slept ${secElapsed} seconds instead of ${secSleep}: " \
+                 "either 'sleep' or \$SECONDS not working"
 fi
+unset -v secElapsed secSleep
 # _
 set abc def
 if	[[ $_ != def ]]
@@ -508,12 +512,11 @@ fi
 function foo
 {
 	typeset SECONDS=0
-	sleep .002
+	sleep 0.002
 	print $SECONDS
-
 }
 x=$(foo)
-(( x >.001 && x < 1 ))
+(( x >= 0.002 && x < 1 ))
 '
 } 2> /dev/null   || err_exit 'SECONDS not working in function'
 cat > $tmp/script <<-\!

src/lib/libast/tm/tvsleep.c

@@ -41,6 +41,8 @@
 # endif
 #endif
 
+#define NANOSECONDS 1000000000L
+
 /*
  * sleep for tv
  * non-zero exit if sleep did not complete
@@ -53,11 +55,12 @@ int
 tvsleep(register const Tv_t* tv, register Tv_t* rv)
 {
 
+	int		r;
+
 #if _lib_nanosleep
 
 	struct timespec	stv;
 	struct timespec	srv;
-	int		r;
 
 	stv.tv_sec = tv->tv_sec;
 	stv.tv_nsec = tv->tv_nsec;
@@ -77,13 +80,11 @@ tvsleep(register const Tv_t* tv, register Tv_t* rv)
 
 #if _lib_select
 
-	struct timeval	stv;
+	struct timeval tvSleep = { tv->tv_sec, tv->tv_nsec / 1000 };
+	if (tv->tv_nsec % 1000)
+		++tvSleep.tv_usec;
 
-	stv.tv_sec = tv->tv_sec;
-	if (!(stv.tv_usec = tv->tv_nsec / 1000))
-		stv.tv_usec = 1;
-	if (select(0, NiL, NiL, NiL, &stv) >= 0)
-		return 0;
+	r = select(0, NiL, NiL, NiL, &tvSleep);
 
 #else
 
@@ -162,51 +163,52 @@ tvsleep(register const Tv_t* tv, register Tv_t* rv)
 
 	if (!(t = (n + 999999L) / 1000000L))
 		t = 1;
-	if (poll(&pfd, 0, t) >= 0)
-		return 0;
+	r = poll(&pfd, 0, t);
 
 #endif
 
 #endif
 
 	}
- bad:
-	if (errno == EINTR && rv)
+
+/* Ascertain whether we actually slept for a sufficient time.
+ * It is preferable to sleep a little more than necessary than too little.
+ */
 	{
-		tvgettime(rv);
-		if (rv->tv_nsec < bv.tv_nsec)
+		struct timespec tsAfter;
+		long sec, nsec;
+
+		tvgettime(&tsAfter);
+
+		/* Calculate seconds left to sleep */
+		sec = (long)(tv->tv_sec + tv->tv_nsec / NANOSECONDS) -
+			((long)tsAfter.tv_sec - (long)bv.tv_sec);
+
+		/* Calculate nanoseconds left to sleep */
+		nsec = (long)(tv->tv_nsec % NANOSECONDS) -
+			((long)tsAfter.tv_nsec - (long)bv.tv_nsec);
+		if (nsec >= NANOSECONDS)
 		{
-			rv->tv_nsec += 1000000000L;
-			rv->tv_sec--;
+			++sec;
+			nsec -= NANOSECONDS;
 		}
-		rv->tv_nsec -= bv.tv_nsec;
-		rv->tv_sec -= bv.tv_sec;
-		if (rv->tv_sec > tv->tv_sec)
+		else if (nsec < 0)
 		{
-			rv->tv_sec = 0;
-			rv->tv_nsec = 0;
+			--sec;
+			nsec += NANOSECONDS;
 		}
-		else
+
+		if (sec >= 0 && (sec > 0 || nsec > 0))
 		{
-			rv->tv_sec = tv->tv_sec - rv->tv_sec;
-			if (rv->tv_nsec > tv->tv_nsec)
+			if (rv)
 			{
-				if (!rv->tv_sec)
-				{
-					rv->tv_sec = 0;
-					rv->tv_nsec = 0;
-				}
-				else
-				{
-					rv->tv_sec--;
-					rv->tv_nsec = 1000000000L - rv->tv_nsec + tv->tv_nsec;
-				}
-			}
-			else
-				rv->tv_nsec = tv->tv_nsec - rv->tv_nsec;
-		}
+				rv->tv_sec  = sec;
+				rv->tv_nsec = nsec;
 			}
 			return -1;
+		}
+	}
+	return r;
 
 #endif