gc_during_func.go

package main

import (
	"fmt"
	"runtime"
)

func main() {
	var stats runtime.MemStats

	runtime.ReadMemStats(&stats)
	fmt.Printf("initial:\nalloc=%d inuse=%d released=%d\n\n", stats.HeapAlloc, stats.HeapInuse, stats.HeapReleased)

	var bigVar [][]int
	for i := 0; i < 10; i++ {
		bigVar = append(bigVar, make([]int, 100000))
	}

	runtime.ReadMemStats(&stats)
	fmt.Printf("after big var:\nalloc=%d inuse=%d released=%d\n\n", stats.HeapAlloc, stats.HeapInuse, stats.HeapReleased)

	runtime.GC()

	bigVar[0] = make([]int, 100000)

	runtime.ReadMemStats(&stats)
	fmt.Printf("big var still in use:\nalloc=%d inuse=%d released=%d\n\n", stats.HeapAlloc, stats.HeapInuse, stats.HeapReleased)

	runtime.GC()

	runtime.ReadMemStats(&stats)
	fmt.Printf("big var no longer in use:\nalloc=%d inuse=%d released=%d\n\n", stats.HeapAlloc, stats.HeapInuse, stats.HeapReleased)
}

initial:
alloc=102384 inuse=450560 released=3448832

after big var:
alloc=8137256 inuse=8486912 released=3661824

big var still in use:
alloc=8939816 inuse=9281536 released=2826240

big var no longer in use:
alloc=108456 inuse=442368 released=2793472

In this example, GC is triggered explicitly for determinism. But it can trigger automatically at the time of any function call.