goroutine leak at cache.go:1079 - `runJanitor`

[tigerinus]

package main

import (
	"testing"
	"time"

	"github.com/patrickmn/go-cache"
	"go.uber.org/goleak"
)

func leaktest(t *testing.T) {
	defer goleak.VerifyNone(t)
	cache.New(5*time.Minute, 10*time.Minute)
}

func main() {
	testSuite := []testing.InternalTest{{Name: "leaktest", F: leaktest}}
	testing.Main(func(a, b string) (bool, error) { return a == b, nil }, testSuite, nil, nil)
}

Run above code (https://go.dev/play/p/PxN4Q4-F2rG)

Result:

        [Goroutine 6 in state select, with github.com/patrickmn/go-cache.(*janitor).Run on top of the stack:
        goroutine 6 [select]:
        github.com/patrickmn/go-cache.(*janitor).Run(0xc0002f16d0, 0x0?)
        	/home/wxh/go/pkg/mod/github.com/patrickmn/go-cache@v2.1.0+incompatible/cache.go:1079 +0x85
        created by github.com/patrickmn/go-cache.runJanitor
        	/home/wxh/go/pkg/mod/github.com/patrickmn/go-cache@v2.1.0+incompatible/cache.go:1099 +0xed
        ]

It looks like https://github.com/patrickmn/go-cache/blob/v2.1.0/cache.go#L1076-L1087 does not handle exit condition properly.

[vithnilica]

it's work

import (
	"runtime"
	"testing"
	"time"

	"github.com/patrickmn/go-cache"
	"go.uber.org/goleak"
)

func leaktest(t *testing.T) {
	defer goleak.VerifyNone(t)
	cache.New(5*time.Minute, 10*time.Minute)
	runtime.GC()
}

func main() {
	testSuite := []testing.InternalTest{{Name: "leaktest", F: leaktest}}
	testing.Main(func(a, b string) (bool, error) { return a == b, nil }, testSuite, nil, nil)
}

[ponder2000]

I am also getting the similar kind of error as follows

range_service  | goroutine 876 [select, 2 minutes]:
range_service  | github.com/patrickmn/go-cache.(*janitor).Run(0xc001627fb0, 0xc0011b9140?)
range_service  | 	/Users/jay/go/pkg/mod/github.com/patrickmn/go-cache@v2.1.0+incompatible/cache.go:1079 +0x85
range_service  | created by github.com/patrickmn/go-cache.runJanitor
range_service  | 	/Users/jay/go/pkg/mod/github.com/patrickmn/go-cache@v2.1.0+incompatible/cache.go:1099 +0xed
range_service  |
range_service  | goroutine 877 [select, 5 minutes]:
range_service  | github.com/patrickmn/go-cache.(*janitor).Run(0xc001634050, 0x0?)
range_service  | 	/Users/jay/go/pkg/mod/github.com/patrickmn/go-cache@v2.1.0+incompatible/cache.go:1079 +0x85
range_service  | created by github.com/patrickmn/go-cache.runJanitor
range_service  | 	/Users/jay/go/pkg/mod/github.com/patrickmn/go-cache@v2.1.0+incompatible/cache.go:1099 +0xed

@vithnilica Can you explain how runtime.GC() is helping and when to call this function. I am really new to go and don't understand much about memory leaks and all so can you please give an example to explain it better.

Thanks

[vithnilica]

It is not memory leaks (or goroutine leak). "go.uber.org/goleak" test does not wait for "garbage collector".

[ponder2000]

It is not memory leaks (or goroutine leak). "go.uber.org/goleak" test does not wait for "garbage collector".

Can you please explain why I am getting the error(cause of the error) and how will adding a routine.GC() after every cache creation helps to resolve the error.

[vithnilica]

The test counts the number of goroutines at the beginning and at the end. You need to clean up the memory (garbage collection) before terminating the test. Golang typically does this with a delay. Before releasing an object from memory, the Golang calls a finalizer that terminates the goroutine.
Finalizer registration in code: https://github.com/patrickmn/go-cache/blob/master/cache.go#L1123
About finalizer: https://medium.com/a-journey-with-go/go-finalizers-786df8e17687
About garbage collection: https://tip.golang.org/doc/gc-guide