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Merge pull request #4367 from nvanbenschoten/nvanbenschoten/timers
Allocate timers outside of loops to avoid repeat allocations
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,79 @@ | ||
| // Copyright 2016 The Cockroach Authors. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or | ||
| // implied. See the License for the specific language governing | ||
| // permissions and limitations under the License. | ||
| // | ||
| // Author: Nathan VanBenschoten (nvanbenschoten@gmail.com) | ||
|
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| package util | ||
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| import "time" | ||
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| // The Timer type represents a single event. When the Timer expires, | ||
| // the current time will be sent on Timer.C. | ||
| // | ||
| // This timer implementation is an abstraction around the standard | ||
| // library's time.Timer that provides a temporary workaround for the | ||
| // issue described in https://github.com/golang/go/issues/14038. As | ||
| // such, this timer should only be used when Reset is planned to | ||
| // be called continually in a loop. For this Reset pattern to work, | ||
| // Timer.Read must be set to true whenever a timestamp is read from | ||
| // the Timer.C channel. If Timer.Read is not set to true when the | ||
| // channel is read from, the next call to Timer.Reset will deadlock. | ||
| // This pattern looks something like: | ||
| // | ||
| // var timer util.Timer | ||
| // defer timer.Stop() | ||
| // for { | ||
| // timer.Reset(wait) | ||
| // switch { | ||
| // case <-timer.C: | ||
| // timer.Read = true | ||
| // ... | ||
| // } | ||
| // } | ||
| // | ||
| // Note that unlike the standard library's Timer type, this Timer will | ||
| // not begin counting down until Reset is called for the first time, as | ||
| // there is no constructor function. | ||
| type Timer struct { | ||
| *time.Timer | ||
| Read bool | ||
| } | ||
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| // Reset changes the timer to expire after duration d and returns | ||
| // the new value of the timer. This method includes the fix proposed | ||
| // in https://github.com/golang/go/issues/11513#issuecomment-157062583, | ||
| // but requires users of Timer to set Timer.Read to true whenever | ||
| // they successfully read from the Timer's channel. Reset operates on | ||
| // and returns a value so that Timer can be stack allocated. | ||
| func (t *Timer) Reset(d time.Duration) { | ||
| if t.Timer == nil { | ||
| t.Timer = time.NewTimer(d) | ||
| return | ||
| } | ||
| if !t.Timer.Reset(d) && !t.Read { | ||
| <-t.C | ||
| } | ||
| t.Read = false | ||
| } | ||
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| // Stop prevents the Timer from firing. It returns true if the call stops | ||
| // the timer, false if the timer has already expired, been stopped previously, | ||
| // or had never been initialized with a call to Timer.Reset. Stop does not | ||
| // close the channel, to prevent a read from succeeding incorrectly. | ||
| func (t *Timer) Stop() bool { | ||
| if t.Timer == nil { | ||
| return false | ||
| } | ||
| return t.Timer.Stop() | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,127 @@ | ||
| // Copyright 2016 The Cockroach Authors. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or | ||
| // implied. See the License for the specific language governing | ||
| // permissions and limitations under the License. | ||
| // | ||
| // Author: Nathan VanBenschoten (nvanbenschoten@gmail.com) | ||
|
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| package util | ||
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| import ( | ||
| "testing" | ||
| "time" | ||
| ) | ||
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| const timeStep = 10 * time.Millisecond | ||
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| func TestTimerTimeout(t *testing.T) { | ||
| var timer Timer | ||
| defer func() { | ||
| if stopped := timer.Stop(); stopped { | ||
| t.Errorf("expected Stop to return false, got true") | ||
| } | ||
| }() | ||
| timer.Reset(timeStep) | ||
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| <-timer.C | ||
| timer.Read = true | ||
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| select { | ||
| case <-timer.C: | ||
| t.Errorf("expected timer to only timeout once after Reset; got two timeouts") | ||
| case <-time.After(5 * timeStep): | ||
| } | ||
| } | ||
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| func TestTimerStop(t *testing.T) { | ||
| var timer Timer | ||
| timer.Reset(timeStep) | ||
| if stopped := timer.Stop(); !stopped { | ||
| t.Errorf("expected Stop to return true, got false") | ||
| } | ||
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| select { | ||
| case <-timer.C: | ||
| t.Errorf("expected timer to stop after call to Stop; got timer that was not stopped") | ||
| case <-time.After(5 * timeStep): | ||
| } | ||
| } | ||
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| func TestTimerUninitializedStopNoop(t *testing.T) { | ||
| var timer Timer | ||
| if stopped := timer.Stop(); stopped { | ||
| t.Errorf("expected Stop to return false when the timer was never reset, got true") | ||
| } | ||
| } | ||
|
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| func TestTimerResetBeforeTimeout(t *testing.T) { | ||
| var timer Timer | ||
| defer timer.Stop() | ||
| timer.Reset(timeStep) | ||
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| timer.Reset(timeStep) | ||
| <-timer.C | ||
| timer.Read = true | ||
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| select { | ||
| case <-timer.C: | ||
| t.Errorf("expected timer to only timeout once after Reset; got two timeouts") | ||
| case <-time.After(5 * timeStep): | ||
| } | ||
| } | ||
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| func TestTimerResetAfterTimeoutAndNoRead(t *testing.T) { | ||
| var timer Timer | ||
| defer timer.Stop() | ||
| timer.Reset(timeStep) | ||
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| time.Sleep(2 * timeStep) | ||
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| timer.Reset(timeStep) | ||
| <-timer.C | ||
| timer.Read = true | ||
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| select { | ||
| case <-timer.C: | ||
| t.Errorf("expected timer to only timeout once after Reset; got two timeouts") | ||
| case <-time.After(5 * timeStep): | ||
| } | ||
| } | ||
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| func TestTimerResetAfterTimeoutAndRead(t *testing.T) { | ||
| var timer Timer | ||
| defer timer.Stop() | ||
| timer.Reset(timeStep) | ||
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| <-timer.C | ||
| timer.Read = true | ||
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| timer.Reset(timeStep) | ||
| <-timer.C | ||
| timer.Read = true | ||
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| select { | ||
| case <-timer.C: | ||
| t.Errorf("expected timer to only timeout once after Reset; got two timeouts") | ||
| case <-time.After(5 * timeStep): | ||
| } | ||
| } | ||
|
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| func TestTimerMakesProgressInLoop(t *testing.T) { | ||
| var timer Timer | ||
| defer timer.Stop() | ||
| for i := 0; i < 5; i++ { | ||
| timer.Reset(timeStep) | ||
| <-timer.C | ||
| timer.Read = true | ||
| } | ||
| } |