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time: document that Tick interval gap can exceed duration #30271

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xsigndll opened this issue Feb 16, 2019 · 6 comments
Closed

time: document that Tick interval gap can exceed duration #30271

xsigndll opened this issue Feb 16, 2019 · 6 comments
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Documentation FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@xsigndll
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What version of Go are you using (go version)?

go version go1.11.5 windows/amd64

What did you do?

The documentation example for time.Tick ( https://golang.org/pkg/time/#Tick ) states that the channel returns now. But if the routine inside the tick exceeds the duration, the ticker produces a one-time gap. This may need clarification in the documentation example. You may check this playground example: https://play.golang.org/p/ImIhZTLYciq

package main

import (
	"fmt"
	"time"
)

func main() {
	c := time.Tick(1 * time.Second)
	for now := range c {
		fmt.Printf("now\t\t%v\n", now)
		fmt.Printf("time.Now()\t%v\n", time.Now())
		time.Sleep(3 * time.Second)
	}
}

What did you expect to see?

time.Now() should be the same as now.

What did you see instead?

It produces a gap in the second interval:

now		2009-11-10 23:00:01 +0000 UTC m=+1.000000001
time.Now()	2009-11-10 23:00:01 +0000 UTC m=+1.000000001
now		2009-11-10 23:00:02 +0000 UTC m=+2.000000001
time.Now()	2009-11-10 23:00:04 +0000 UTC m=+4.000000001  <==== +2s
now		2009-11-10 23:00:05 +0000 UTC m=+5.000000001
time.Now()	2009-11-10 23:00:07 +0000 UTC m=+7.000000001
now		2009-11-10 23:00:08 +0000 UTC m=+8.000000001
time.Now()	2009-11-10 23:00:10 +0000 UTC m=+10.000000001
now		2009-11-10 23:00:11 +0000 UTC m=+11.000000001
time.Now()	2009-11-10 23:00:13 +0000 UTC m=+13.000000001
@agnivade
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It is mentioned that Tick is a convenience wrapper for NewTicker and the behavior you mention is written in https://golang.org/pkg/time/#NewTicker - It adjusts the intervals or drops ticks to make up for slow receivers.

@xsigndll
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Correct. But „adjusting the interval“ implies that the channel returns the new corrected time („now“), which is not the case. I still think that the documentation should be corrected for time.Tick to prevent people from thinkin that the channel always returns „now“.

@agnivade
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/cc @ianlancetaylor

@agnivade agnivade added Documentation NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Feb 17, 2019
@agnivade agnivade changed the title time.Tick interval gap if duration exceeded time: document that Tick interval gap can exceed duration Feb 17, 2019
@ianlancetaylor ianlancetaylor added this to the Go1.13 milestone Feb 19, 2019
@ianlancetaylor
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Shall we just change the variable name now in ExampleTick to next? Or t?

@xsigndll
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I would go for next

@andybons andybons modified the milestones: Go1.13, Go1.14 Jul 8, 2019
@rsc rsc modified the milestones: Go1.14, Backlog Oct 9, 2019
@gopherbot
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Change https://golang.org/cl/206123 mentions this issue: time: change variable name to next

@golang golang locked and limited conversation to collaborators Nov 9, 2020
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@rsc @xsigndll @andybons @agnivade @ianlancetaylor @gopherbot