Test memory

gistfile1.txt

package main

import (
	"bufio"
	"fmt"
	"os"
	"runtime"
	"strings"
)

func printOutMemoryUsage() {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)

	rss := getRSS()

	fmt.Println("      HeapAlloc | HeapSys | HeapIdle | HeapInUse | RSS")
	fmt.Printf("Memory:  %6d | %7d | %8d | %9d | %3d\n",
		m.HeapAlloc/1024/1024, m.HeapSys/1024/1024, m.HeapIdle/1024/1024,
		m.HeapInuse/1024/1024, rss/1024)
}

// getRSS returns the Resident Set Size in bytes by reading /proc/self/status.
func getRSS() uint64 {
	file, err := os.Open("/proc/self/status")
	if err != nil {
		return 0
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := scanner.Text()
		if strings.HasPrefix(line, "VmRSS:") {
			fields := strings.Fields(line)
			if len(fields) >= 2 {
				var rss uint64
				_, err := fmt.Sscanf(fields[1], "%d", &rss)
				if err != nil {
					return 0
				}
				// VmRSS in /proc/self/status is in kB, convert to bytes
				return rss
			}
		}
	}
	return 0
}

type A struct {
	a int
	b int
	c int
}

func main() {
	fmt.Print(`=== Memory Usage Statistics ===
Heap Alloc   - Currently allocated heap objects
Heap Sys     - Heap memory obtained from OS
Heap Idle    - Idle spans waiting to be released
Heap InUse   - In-use spans (cannot be released)`)

	fmt.Println("\n\n === Fresh start ===")
	printOutMemoryUsage()

	fmt.Println("\n === Allocated array ===")
	lInt := 1000_000_000
	lPtr := 100_000_000
	// a := make([]int, lInt)
	a := make([]*A, lPtr)
	_, _ = lPtr, lInt
	l := len(a)
	fmt.Printf("Len: %d, Cap: %d\n", len(a), cap(a))
	printOutMemoryUsage()

	fmt.Println("\n === Fill array ===")
	for i := range l {
		// a[i] = i
		a[i] = &A{a: i, b: i, c: i}
	}
	fmt.Printf("Len: %d, Cap: %d\n", len(a), cap(a))
	printOutMemoryUsage()

	fmt.Println("\n === Clear array ===")
	// clear(a)
	a = a[:0]
	runtime.GC()
	fmt.Printf("Len: %d, Cap: %d\n", len(a), cap(a))
	printOutMemoryUsage()

	fmt.Println("\n === Re-fill array ===")
	for i := 0; i < l; i++ {
		// a = append(a, i)
		a = append(a, &A{a: i, b: i, c: i})
	}
	runtime.GC()
	fmt.Printf("Len: %d, Cap: %d\n", len(a), cap(a))
	printOutMemoryUsage()
}