fmt: incorrect usage of sync.Pool #27740
Description
type CustomStringer int
func (c CustomStringer) String() string {
time.Sleep(500 * time.Millisecond) // simulate processing time
return string(make([]byte, int(c)))
}
func main() {
processRequest := func(size int) {
fmt.Sprintf("<%v>", CustomStringer(size))
time.Sleep(1 * time.Millisecond) // simulate idle time
}
// Simulate a steady stream of infrequent large requests.
go func() {
for {
processRequest(1 << 28) // 256MiB
}
}()
// Simulate a storm of small requests.
for i := 0; i < 1000; i++ {
go func() {
for {
processRequest(1 << 10) // 1KiB
}
}()
}
// Continually run a GC and track the allocated bytes.
var stats runtime.MemStats
for i := 0; ; i++ {
runtime.ReadMemStats(&stats)
fmt.Printf("Cycle %d: %dB\n", i, stats.Alloc)
time.Sleep(time.Second)
runtime.GC()
}
}This is a variation of #23199 (comment). See that comment for why this memory leak occurs.
After the 50th GC cycle, this pins 7GiB of heap, when I expect it to use no more than 256MiB.