A timer that helps with the pitfalls of using golang timers in loops.
For example, the following code leaks timers because time.After() does not garbage collect until the timer expires:
for {
select {
case somePayload, ok := <-someChan:
if !ok {
// channel is closed exit
return
}
doSomething()
checkSomethingLoop::
for _, foo := range someSlice {
// It's possible we could block for a long time on writing to channel. If we cant write after Xms abort
select {
case writeChan <- "foo":
doSomething
case <-time.After(time.Duration(25) * time.Millisecond):
break checkSomethingLoop
}
}
}
}See: https://pkg.go.dev/time#After
The obvious solution is to use timer := time.NewTimer(time.Duration(25) * time.Millisecond) before the loop and reset it, but it turns out this has complications: https://pkg.go.dev/time#NewTimer golang/go#11513
CockroachDB has a nice solution to encapsulate the complexity. This code is copied from CockroachDB when it was released under an Apache license in 2019: https://github.com/cockroachdb/cockroach/blob/4d82429ba71d1d2a868ebff38f6d8f7ce3595d21/pkg/util/timeutil/timer.go
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 workaround for the issue described in golang/go#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.
Example:
var tmr timer.Timer
defer tmr.Stop()
for {
tmr.Reset(wait)
select {
case <-tmr.C:
tmr.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.
Happy to accept PRs.
davidwartell
Released under the Apache License.