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Use a custom clock interface and fake clock implementation
The fake clock provided as part of k8s.io/utils has some limitations: it does not conform to the specifications of the standard library time package when it comes to timers (e.g., Stop() does not return false if the timer has already been stopped), and it prevents (deadlock) clock methods such as Now() (but also the Stop() method of timers) from being called while executing a timer function (timer created with AfterFunc). To avoid non-intuitive workarounds in our code caused by these limitations, we define our own clock interface and fake clock implementation. This does not represent too much code, as the CollectingProcess only uses a limited amount of clock functions. Signed-off-by: Antonin Bas <antonin.bas@broadcom.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,156 @@ | ||
| // Copyright 2024 VMware, Inc. | ||
| // | ||
| // 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. | ||
|
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| package collector | ||
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|
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| import ( | ||
| "sync" | ||
| "time" | ||
| ) | ||
|
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| // timer allows for injecting fake or real timers into code that needs to do arbitrary things based | ||
| // on time. We do not include the C() method, as we only support timers created with AfterFunc. | ||
| type timer interface { | ||
| Stop() bool | ||
| Reset(d time.Duration) bool | ||
| } | ||
|
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| // clock allows for injecting fake or real clocks into code that needs to do arbitrary things based | ||
| // on time. We only support a very limited interface at the moment, with only the methods required | ||
| // by CollectingProcess. | ||
| type clock interface { | ||
| Now() time.Time | ||
| AfterFunc(d time.Duration, f func()) timer | ||
| } | ||
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| // realClock implements the clock interface using functions from the time package. | ||
| type realClock struct{} | ||
|
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| func (realClock) Now() time.Time { | ||
| return time.Now() | ||
| } | ||
|
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| func (realClock) AfterFunc(d time.Duration, f func()) timer { | ||
| return time.AfterFunc(d, f) | ||
| } | ||
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| type fakeTimer struct { | ||
| targetTime time.Time | ||
| f func() | ||
| clock *fakeClock | ||
| } | ||
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| func (t *fakeTimer) Stop() bool { | ||
| clock := t.clock | ||
| clock.m.Lock() | ||
| defer clock.m.Unlock() | ||
| newTimers := make([]*fakeTimer, 0, len(clock.timers)) | ||
| fired := true | ||
| for i := range clock.timers { | ||
| if clock.timers[i] != t { | ||
| newTimers = append(newTimers, t) | ||
| continue | ||
| } | ||
| // timer is found so it hasn't been fired yet | ||
| fired = false | ||
| } | ||
| clock.timers = newTimers | ||
| return !fired | ||
| } | ||
|
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| func (t *fakeTimer) Reset(d time.Duration) bool { | ||
| clock := t.clock | ||
| clock.m.Lock() | ||
| defer clock.m.Unlock() | ||
| fired := true | ||
| for i := range clock.timers { | ||
| if clock.timers[i] != t { | ||
| continue | ||
| } | ||
| // timer is found so it hasn't been fired yet | ||
| fired = false | ||
| t.targetTime = clock.now.Add(d) | ||
| } | ||
| return !fired | ||
| } | ||
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| // fakeClock implements the clock interface as a virtual clock meant to be used in tests. Time can | ||
| // be advanced arbitrarily, but does not change on its own. | ||
| type fakeClock struct { | ||
| m sync.RWMutex | ||
| isAdvancing bool | ||
| now time.Time | ||
| timers []*fakeTimer | ||
| } | ||
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| func newFakeClock(t time.Time) *fakeClock { | ||
| return &fakeClock{ | ||
| now: t, | ||
| } | ||
| } | ||
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| func (c *fakeClock) Now() time.Time { | ||
| c.m.RLock() | ||
| defer c.m.RUnlock() | ||
| return c.now | ||
| } | ||
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| func (c *fakeClock) AfterFunc(d time.Duration, f func()) timer { | ||
| if d <= 0 { | ||
| panic("negative duration not supported") | ||
| } | ||
| c.m.Lock() | ||
| defer c.m.Unlock() | ||
| t := &fakeTimer{ | ||
| targetTime: c.now.Add(d), | ||
| f: f, | ||
| clock: c, | ||
| } | ||
| c.timers = append(c.timers, t) | ||
| return t | ||
| } | ||
|
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| func (c *fakeClock) Step(d time.Duration) { | ||
| if d < 0 { | ||
| panic("invalid duration") | ||
| } | ||
| timerFuncs := []func(){} | ||
| func() { | ||
| c.m.Lock() | ||
| defer c.m.Unlock() | ||
| if c.isAdvancing { | ||
| panic("concurrent calls to Step() not allowed") | ||
| } | ||
| c.isAdvancing = true | ||
| c.now = c.now.Add(d) | ||
| // Collect timer functions to run and remove them from list. | ||
| newTimers := make([]*fakeTimer, 0, len(c.timers)) | ||
| for _, t := range c.timers { | ||
| if !t.targetTime.After(c.now) { | ||
| timerFuncs = append(timerFuncs, t.f) | ||
| } else { | ||
| newTimers = append(newTimers, t) | ||
| } | ||
| } | ||
| c.timers = newTimers | ||
| }() | ||
| // Run the timer functions, without holding a lock. This allows these functions to call | ||
| // clock.Now(), but also timer.Stop(). | ||
| for _, f := range timerFuncs { | ||
| f() | ||
| } | ||
| c.m.Lock() | ||
| defer c.m.Unlock() | ||
| c.isAdvancing = false | ||
| } |
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