From 6478df1c418421cd3a148f77d732ce4c57486314 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Mon, 8 Dec 2008 17:45:50 -0800
Subject: [PATCH] avoid skew in time.Tick; remove errors from time.Seconds,
 time.Nanoseconds

R=r
DELTA=46  (21 added, 10 deleted, 15 changed)
OCL=20785
CL=20787
---
 src/lib/time/tick.go      | 23 ++++++++++++++++++++---
 src/lib/time/tick_test.go |  4 ++--
 src/lib/time/time.go      | 34 ++++++++++++++--------------------
 3 files changed, 36 insertions(+), 25 deletions(-)

diff --git a/src/lib/time/tick.go b/src/lib/time/tick.go
index efd5ceb256..d8f7eae09d 100644
--- a/src/lib/time/tick.go
+++ b/src/lib/time/tick.go
@@ -26,15 +26,32 @@ import (
 
 func Ticker(ns int64, c *chan int64) {
 	var tv syscall.Timeval;
+	now := time.Nanoseconds();
+	when := now;
 	for {
-		syscall.nstotimeval(ns, &tv);
+		when += ns;	// next alarm
+		
+		// if c <- now took too long, skip ahead
+		if when < now {
+			// one big step
+			when += (now-when)/ns * ns;
+		}
+		for when <= now {
+			// little steps until when > now
+			when += ns
+		}
+
+		syscall.nstotimeval(when - now, &tv);
 		syscall.Syscall6(syscall.SYS_SELECT, 0, 0, 0, 0, syscall.TimevalPtr(&tv), 0);
-		nsec, err := time.Nanoseconds();
-		c <- nsec;
+		now = time.Nanoseconds();
+		c <- now;
 	}
 }
 
 export func Tick(ns int64) *chan int64 {
+	if ns <= 0 {
+		return nil
+	}
 	c := new(chan int64);
 	go Ticker(ns, c);
 	return c;
diff --git a/src/lib/time/tick_test.go b/src/lib/time/tick_test.go
index 9530f62778..f9b18fc1d9 100644
--- a/src/lib/time/tick_test.go
+++ b/src/lib/time/tick_test.go
@@ -15,11 +15,11 @@ export func TestTick(t *testing.T) {
 		Count uint64 = 10;
 	);
 	c := Tick(Delta);
-	t0, err := Nanoseconds();
+	t0 := Nanoseconds();
 	for i := 0; i < Count; i++ {
 		<-c;
 	}
-	t1, err1 := Nanoseconds();
+	t1 := Nanoseconds();
 	ns := t1 - t0;
 	target := int64(Delta*Count);
 	slop := target*2/10;
diff --git a/src/lib/time/time.go b/src/lib/time/time.go
index b539c385a6..e71e73b2ef 100644
--- a/src/lib/time/time.go
+++ b/src/lib/time/time.go
@@ -10,17 +10,21 @@ import (
 )
 
 // Seconds since January 1, 1970 00:00:00 GMT
-export func Seconds() (sec int64, err *os.Error) {
-	var nsec int64;
-	sec, nsec, err = os.Time();
-	return sec, err
+export func Seconds() int64 {
+	sec, nsec, err := os.Time();
+	if err != nil {
+		panic("time: os.Time: ", err.String());
+	}
+	return sec
 }
 
 // Nanoseconds since January 1, 1970 00:00:00 GMT
-export func Nanoseconds() (nsec int64, err *os.Error) {
-	var sec int64;
-	sec, nsec, err = os.Time();
-	return sec*1e9 + nsec, err
+export func Nanoseconds() int64 {
+	sec, nsec, err := os.Time();
+	if err != nil {
+		panic("time: os.Time: ", err.String());
+	}
+	return sec*1e9 + nsec
 }
 
 export const (
@@ -142,12 +146,7 @@ export func SecondsToUTC(sec int64) *Time {
 }
 
 export func UTC() (t *Time, err *os.Error) {
-	var sec int64;
-	sec, err = Seconds();
-	if err != nil {
-		return nil, err
-	}
-	return SecondsToUTC(sec), nil
+	return SecondsToUTC(Seconds()), nil
 }
 
 // TODO: Should this return an error?
@@ -163,12 +162,7 @@ export func SecondsToLocalTime(sec int64) *Time {
 }
 
 export func LocalTime() (t *Time, err *os.Error) {
-	var sec int64;
-	sec, err = Seconds();
-	if err != nil {
-		return nil, err
-	}
-	return SecondsToLocalTime(sec), nil
+	return SecondsToLocalTime(Seconds()), nil
 }
 
 // Compute number of seconds since January 1, 1970.
-- 
2.48.1