125 lines
3.1 KiB
Go
125 lines
3.1 KiB
Go
// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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// For more tutorials : https://learngoprogramming.com
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// In-person training : https://www.linkedin.com/in/inancgumus/
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// Follow me on twitter: https://twitter.com/inancgumus
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package main
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import (
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"fmt"
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"io/ioutil"
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"github.com/inancgumus/learngo/16-slices/exercises/24-fix-the-memory-leak/api"
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)
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// ---------------------------------------------------------
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// EXERCISE: Fix the memory leak
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//
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// WARNING
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//
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// This is a very difficult exercise. You need to
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// do some research on your own to solve it. Please don't
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// get discouraged if you can't solve it yet.
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//
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//
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// GOAL
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//
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// In this exercise, your goal is to reduce the memory
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// usage. To do that, you need to find and fix the memory
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// leak within `main()`.
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//
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//
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// PROBLEM
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//
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// `main()` calls `api.Report()` that reports the current
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// memory usage.
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//
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// After that, `main()` calls `api.Read()` that returns
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// a slice with 10 millions of elements. But you only need
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// the last 10 elements of the returned slice.
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//
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//
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// WHAT YOU NEED TO DO
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//
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// You only need to change the code in `main()`. Please
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// do not touch the code in `api/api.go`.
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//
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//
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// CURRENT OUTPUT
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//
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// > Memory Usage: 113 KB
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//
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// Last 10 elements: [...]
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//
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// > Memory Usage: 65651 KB
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//
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// + Before `api.Read()` call: It uses 113 KB of memory.
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//
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// + After `api.Read()` call : It uses 65 MB of memory.
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//
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// + This means that, `main()` never releases the memory.
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// This is the leak.
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//
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// + Your goal is to release the unused memory. Remember,
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// you only need 10 elements but in the current code
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// below you have a slice with 10 millions of elements.
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//
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//
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// EXPECTED OUTPUT
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//
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// > Memory Usage: 116 KB
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//
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// Last 10 elements: [...]
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//
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// > Memory Usage: 118 KB
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//
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// + In the expected output, `main()` releases the memory.
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//
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// It no longer uses 65 MB of memory. Instead, it only
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// uses 118 KB of memory. That's why the second
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// `api.Report()` call reports 118 KB.
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//
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//
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// ADDITIONAL NOTE
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//
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// Memory leak means: Your program is using unnecessary
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// computer memory. It doesn't release memory that is
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// no longer needed.
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//
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// See this for more information:
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// https://en.wikipedia.org/wiki/Memory_leak
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//
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//
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// HINTS
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//
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// Check out `hints.md` file if you get stuck.
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//
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// ---------------------------------------------------------
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func main() {
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// reports the initial memory usage
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api.Report()
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// returns a slice with 10 million elements.
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// it allocates 65 MB of memory space.
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millions := api.Read()
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// -----------------------------------------------------
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// ✪ ONLY CHANGE THE CODE IN THIS AREA ✪
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last10 := millions[len(millions)-10:]
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fmt.Printf("\nLast 10 elements: %d\n\n", last10)
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// ✪ ONLY CHANGE THE CODE IN THIS AREA ✪
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// -----------------------------------------------------
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api.Report()
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// don't worry about this code.
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fmt.Fprintln(ioutil.Discard, millions[0])
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}
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