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refactor: slice exercises 22 and 24

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This commit is contained in:
Inanc Gumus
2019-08-22 20:55:47 +03:00
parent 792a7a75d4
commit 08d881a3d0
6 changed files with 126 additions and 73 deletions
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24
16-slices/exercises/22-adv-ops-practice/main.go
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@ -16,18 +16,6 @@ import (
// ---------------------------------------------------------
func main() {
//
// Use the prettyslice package for printing the slices,
// or do it with your own Printf that matches the output
// of the prettyslice package.
//
// This allows you to see the backing array of the slices.
s.PrintBacking = true
// Shows 10 slice elements per line
s.MaxPerLine = 10
// Prints 60 character per line
s.Width = 60
// ########################################################
//
// #1: Create a string slice: `names` with a length and
@ -127,3 +115,15 @@ func main() {
// ...
// s.Show("6th step", clone, sliced)
}
//
// Don't mind about this function.
//
// For printing the slices: You can either use the
// prettyslice package or `fmt.Printf`.
//
func init() {
s.PrintBacking = true // prints the backing array
s.MaxPerLine = 10 // prints 10 slice elements per line
s.Width = 60 // prints 60 character per line
}

16
16-slices/exercises/22-adv-ops-practice/solution/main.go
View File

@ -12,10 +12,6 @@ import (
)
func main() {
s.PrintBacking = true
s.MaxPerLine = 10
s.Width = 60
// ########################################################
//
// #1: Create a string slice: `names` with a length and
@ -115,3 +111,15 @@ func main() {
s.Show("6th step", clone, sliced)
}
//
// Don't mind about this function.
//
// For printing the slices: You can either use the
// prettyslice package or `fmt.Printf`.
//
func init() {
s.PrintBacking = true // prints the backing array
s.MaxPerLine = 10 // prints 10 slice elements per line
s.Width = 60 // prints 60 character per line
}

4
16-slices/exercises/24-fix-the-memory-leak/api/api.go
View File

@ -6,9 +6,7 @@ import (
"runtime"
)
// DO NOT TOUCH THE FOLLOWING CODE
// THIS IS THE IMAGINARY API CODE
// YOU CANNOT CONTROL IT!
// DO NOT TOUCH THIS FILE BUT YOU CAN READ IT
// Read returns a huge slice (allocates ~65 MB of memory)
func Read() []int {

109
16-slices/exercises/24-fix-the-memory-leak/main.go
View File

@ -17,43 +17,94 @@ import (
// ---------------------------------------------------------
// EXERCISE: Fix the memory leak
//
// WARNING! This is a very difficult exercise. You need to
// do some research on your own to solve it. Please don't
// get discouraged if you can't solve it yet.
// WARNING
//
// Imagine that you receive millions of temperature data
// points but you only need the last 10 data points
// (temperatures).
//
// Problem: There is a memory leak in your program.
// Please find the leak and fix it.
//
// Memory leak means: Your program uses computer memory
// unnecessarily. See this: https://en.wikipedia.org/wiki/Memory_leak
// This is a very difficult exercise. You need to
// do some research on your own to solve it. Please don't
// get discouraged if you can't solve it yet.
//
//
// GOAL
//
// In this exercise, your goal is to reduce the memory
// usage. To do that, you need to find and fix the memory
// leak within `main()`.
//
//
// PROBLEM
//
// `main()` calls `api.Report()`. It reports the current
// memory usage.
//
// After that, it calls `api.Read()`. `api.Read()` returns
// a slice with 10 million of elements. But you only need
// the last 10 elements of the returned slice.
//
//
// WHAT YOU NEED TO DO
//
// You only need to change the code in `main()`. Please
// do not touch the code in `api/api.go`.
//
// CURRENT OUTPUT
//
// > Memory Usage: 113 KB
//
// Last 10 elements: [...]
//
// > Memory Usage: 65651 KB
//
// + Before `api.Read()` call: It uses 113 KB of memory.
//
// + After `api.Read()` call : It uses 65 MB of memory.
//
// + This means that, `main()` never releases the memory.
// This is the leak.
//
// + Your goal is to release the unused memory.
//
//
// EXPECTED OUTPUT
//
// > Memory Usage: 116 KB
//
// Last 10 elements: [...]
//
// > Memory Usage: 118 KB
//
// + In the expected output, `main()` releases the memory.
//
// EXPECTED OUTPUT EXPLANATION
// It no longer uses 65 MB of memory. Instead, it only
// uses 118 KB of memory. That's why the second
// `api.Report()` call reports only 118 KB.
//
// In the current program, because of the memory leak,
// the difference is huge: about ~60 MB. Run the program and,
// see it yourself.
//
// Your goal is reducing the memory usage.
// ADDITIONAL NOTE
//
// See the code in api/api.go to see how it allocates
// a huge memory.
// Memory leak means: Your program is using unnecessary
// computer memory. It doesn't release memory that is
// no longer needed.
// See this: https://en.wikipedia.org/wiki/Memory_leak
//
//
// HINTS
//
// Only read this if you get stuck.
//
// + `millions` slice's backing array uses 65 MB of memory.
//
// + Make a new slice with 10 elements, and copy the last
// 10 elements of the `millions` slice to it. This will
// create a new backing array for the new slice only
// with 10 elements.
//
// Then overwrite the `millions` slice by simply
// assigning `last10` slice to it.
//
// Remember: slice = pointer to a backing array.
// If you overwrite the slice, it will lose that
// pointer. So Go can collect the unused memory.
//
// ---------------------------------------------------------
@ -61,20 +112,22 @@ func main() {
// reports the initial memory usage
api.Report()
// reads 65 MB of temperature data into memory!
temps := api.Read()
// returns a slice with 10 million elements.
// it allocates 65 MB of memory space.
millions := api.Read()
// -----------------------------------------------------
// ✪ ONLY ADD YOUR CODE INSIDE THIS BOX ✪
//
// ✪ ONLY CHANGE THE CODE IN THIS AREA ✪
//
// ✪ ONLY ADD YOUR CODE INSIDE THIS BOX ✪
last10 := millions[len(millions)-10:]
fmt.Printf("\nLast 10 elements: %d\n\n", last10)
// ✪ ONLY CHANGE THE CODE IN THIS AREA ✪
// -----------------------------------------------------
// dont touch this code.
api.Report()
// don't worry about this code yet.
fmt.Fprintln(ioutil.Discard, temps[0])
// don't worry about this code.
fmt.Fprintln(ioutil.Discard, millions[0])
}

4
16-slices/exercises/24-fix-the-memory-leak/solution/api/api.go
View File

@ -6,9 +6,7 @@ import (
"runtime"
)
// DO NOT TOUCH THE FOLLOWING CODE
// THIS IS THE IMAGINARY API CODE
// YOU CANNOT CONTROL IT!
// DO NOT TOUCH THIS FILE BUT YOU CAN READ IT
// Read returns a huge slice (allocates ~65 MB of memory)
func Read() []int {

42
16-slices/exercises/24-fix-the-memory-leak/solution/main.go
View File

@ -18,39 +18,35 @@ func main() {
// reports the initial memory usage
api.Report()
// reads 65 MB of temperature data into the memory!
temps := api.Read()
// returns a slice with 10 million elements.
// it allocates 65 MB of memory space.
millions := api.Read()
// ------------------------------------------------------
// SOLUTION #1:
// ------------------------------------------------------
// Copy the last 10 elements of the returned slice
// to a new slice. This will create a new backing array
// only with 10 elements.
last10 := make([]int, 10)
copy(last10, millions[len(millions)-10:])
//
// Copy the last 10 elements of the returned temperatures
// to a new slice.
//
// This will create a new backing array.
//
need := make([]int, 10)
copy(need, temps[len(temps)-10:])
// Make the millions slice lose reference to its backing array
// so that its backing array can be cleaned up from memory.
millions = last10
//
// Make the temp slice lose reference to its backing array
// so that its backing array can be cleaned from the memory.
//
temps = need
// ------------------------------------------------------
// SOLUTION #2:
// ------------------------------------------------------
// Similar to the 1st solution. It does the same thing.
// But this code is more concise. Use this one.
// temps = append([]int(nil), temps[len(temps)-10:]...)
// millions = append([]int(nil), millions[len(millions)-10:]...)
fmt.Printf("\nLast 10 elements: %d\n\n", last10)
// ------------------------------------------------------
// don't worry about this code yet.
api.Report()
fmt.Fprintln(ioutil.Discard, temps[0])
// don't worry about this code yet.
fmt.Fprintln(ioutil.Discard, millions[0])
}