add: slice adv. ops. exercises

16-slices/exercises/24-fix-the-memory-leak/api/api.go

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+package api
+
+import (
+	"fmt"
+	"math/rand"
+	"runtime"
+)
+
+// DO NOT TOUCH THE FOLLOWING CODE
+// THIS IS THE API
+// YOU CANNOT CONTROL IT! :)
+
+// Read returns a huge slice (allocates ~65 MB of memory)
+func Read() []int {
+	return rand.Perm(2 << 22)
+}
+
+// Report cleans the memory and prints the current memory usage
+func Report() {
+	var m runtime.MemStats
+	runtime.GC()
+	runtime.ReadMemStats(&m)
+	fmt.Printf(" > Memory Usage: %v KB\n", m.Alloc/1024)
+}

16-slices/exercises/24-fix-the-memory-leak/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+
+	"github.com/inancgumus/learngo/16-slices/exercises/24-fix-the-memory-leak/api"
+)
+
+// ---------------------------------------------------------
+// EXERCISE: Fix the memory leak
+//
+//  You're receiving millions of temperature data points from
+//  an API, but you only need the last 10 data points.
+//
+//  Currently, there is a memory leak in your program.
+//  Find the leak and fix it.
+//
+//
+// EXPECTED OUTPUT
+//
+//   > Memory Usage: 116 KB
+//   > Memory Usage: 118 KB
+//
+//
+// EXPECTED OUTPUT EXPLANATION
+//
+//   Your output will be different. Your goal is to reduce the
+//   difference between the two measurements of the memory usage.
+//
+//   For the expected output above:
+//
+//     118 KB - 116 KB = Only 2 KB so that's OK.
+//
+//   However, in the current program, because of the memory leak,
+//   the difference is huge: about ~60 MB. Run the program and,
+//   see yourself.
+//
+// ---------------------------------------------------------
+
+func main() {
+	// reports the initial memory usage
+	api.Report()
+
+	// reads 65 MB of temperature data into the memory!
+	temps := api.Read()
+
+	// -----------------------------------------------------
+	// ✪ ONLY ADD YOUR CODE INSIDE THIS BOX ✪
+	//
+
+	//
+	// ✪ ONLY ADD YOUR CODE INSIDE THIS BOX ✪
+	// -----------------------------------------------------
+
+	// fix the problem so that the memory usage stays low
+	// dont touch this code
+	api.Report()
+	fmt.Fprintln(ioutil.Discard, temps[0])
+}

16-slices/exercises/24-fix-the-memory-leak/solution/api/api.go

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+package api
+
+import (
+	"fmt"
+	"math/rand"
+	"runtime"
+)
+
+// DO NOT TOUCH THE FOLLOWING CODE
+// THIS IS THE API
+// YOU CANNOT CONTROL IT! :)
+
+// Read returns a huge slice (allocates ~65 MB of memory)
+func Read() []int {
+	return rand.Perm(2 << 22)
+}
+
+// Report cleans the memory and prints the current memory usage
+func Report() {
+	var m runtime.MemStats
+	runtime.GC()
+	runtime.ReadMemStats(&m)
+	fmt.Printf(" > Memory Usage: %v KB\n", m.Alloc/1024)
+}

16-slices/exercises/24-fix-the-memory-leak/solution/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+
+	"github.com/inancgumus/learngo/16-slices/exercises/24-fix-the-memory-leak/solution/api"
+)
+
+func main() {
+	// reports the initial memory usage
+	api.Report()
+
+	// reads 65 MB of temperature data into the memory!
+	temps := api.Read()
+
+	//
+	// SOLUTION #1:
+	//
+
+	// clone the last 10 elements of the returned temperatures
+	// into a new slice
+	need := make([]int, 10)
+	copy(need, temps[len(temps)-10:])
+	// make the temp slice lose reference to its backing array
+	// so that it can be cleaned from the memory
+	temps = need
+
+	//
+	// SOLUTION #2:
+	//
+
+	// The code below does the same thing like the code above but in one line.
+	// temps = append([]int(nil), temps[len(temps)-10:]...)
+
+	api.Report()
+	fmt.Fprintln(ioutil.Discard, temps[0])
+}