refactor: slices 24th exercise

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

@@ -7,15 +7,29 @@ import (
 )
 
 // DO NOT TOUCH THE FOLLOWING CODE
-// THIS IS THE API
-// YOU CANNOT CONTROL IT! :)
+// THIS IS THE IMAGINARY API CODE
+// YOU CANNOT CONTROL IT!
 
 // Read returns a huge slice (allocates ~65 MB of memory)
 func Read() []int {
+	// 2 << 22 means 2^(22 + 1)
+	// See this: https://en.wikipedia.org/wiki/Arithmetic_shift
+
+	// Perm function returns a slice with random integers in it.
+	// Here it returns a slice with random integers that contains
+	// 8,388,608 elements. One int value is 8 bytes.
+	// So: 8,388,608 * 8 = ~65MB
 	return rand.Perm(2 << 22)
 }
 
 // Report cleans the memory and prints the current memory usage
+// Don't worry about this code. You don't need to understand it.
+//
+// However, if you're curious, read on.
+//
+// The following code runs the garbage collector to clean
+// up the allocated resources, and then it reads the current
+// memory statistics into the m variable.
 func Report() {
 	var m runtime.MemStats
 	runtime.GC()

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

@@ -17,11 +17,25 @@ import (
 // ---------------------------------------------------------
 // EXERCISE: Fix the memory leak
 //
-//  You receive millions of temperature data points from
-//  an API, but you only need the last 10 data points.
+//  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.
 //
-//  Currently, there is a memory leak in your program.
-//  Find the leak and fix it.
+//  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
+//
+//
+// CURRENT OUTPUT
+//
+//   > Memory Usage: 113 KB
+//   > Memory Usage: 65651 KB
 //
 //
 // EXPECTED OUTPUT
@@ -32,16 +46,14 @@ import (
 //
 // EXPECTED OUTPUT EXPLANATION
 //
-//   Your output will be different. Your goal is to reduce the
-//   difference between 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,
+//   In the current program, because of the memory leak,
 //   the difference is huge: about ~60 MB. Run the program and,
-//   see yourself.
+//   see it yourself.
+//
+//   Your goal is reducing the memory usage.
+//
+//   See the code in api/api.go to see how it allocates
+//   a huge memory.
 //
 // ---------------------------------------------------------
 
@@ -49,7 +61,7 @@ func main() {
 	// reports the initial memory usage
 	api.Report()
 
-	// reads 65 MB of temperature data into the memory!
+	// reads 65 MB of temperature data into memory!
 	temps := api.Read()
 
 	// -----------------------------------------------------
@@ -60,8 +72,9 @@ func main() {
 	// ✪ ONLY ADD YOUR CODE INSIDE THIS BOX ✪
 	// -----------------------------------------------------
 
-	// fix the problem so that the memory usage stays low
-	// dont touch this code
+	// dont touch this code.
 	api.Report()
+
+	// don't worry about this code yet.
 	fmt.Fprintln(ioutil.Discard, temps[0])
 }

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

@@ -7,15 +7,29 @@ import (
 )
 
 // DO NOT TOUCH THE FOLLOWING CODE
-// THIS IS THE API
-// YOU CANNOT CONTROL IT! :)
+// THIS IS THE IMAGINARY API CODE
+// YOU CANNOT CONTROL IT!
 
 // Read returns a huge slice (allocates ~65 MB of memory)
 func Read() []int {
+	// 2 << 22 means 2^(22 + 1)
+	// See this: https://en.wikipedia.org/wiki/Arithmetic_shift
+
+	// Perm function returns a slice with random integers in it.
+	// Here it returns a slice with random integers that contains
+	// 8,388,608 elements. One int value is 8 bytes.
+	// So: 8,388,608 * 8 = ~65MB
 	return rand.Perm(2 << 22)
 }
 
 // Report cleans the memory and prints the current memory usage
+// Don't worry about this code. You don't need to understand it.
+//
+// However, if you're curious, read on.
+//
+// The following code runs the garbage collector to clean
+// up the allocated resources, and then it reads the current
+// memory statistics into the m variable.
 func Report() {
 	var m runtime.MemStats
 	runtime.GC()

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

@@ -21,25 +21,36 @@ func main() {
 	// 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
+	//
+	// 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 temp slice lose reference to its backing array
-	// so that it can be cleaned from the memory
+
+	//
+	// 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.
 
-	// The code below does the same thing like the code above but in one line.
 	// temps = append([]int(nil), temps[len(temps)-10:]...)
 
+	// ------------------------------------------------------
+	// don't worry about this code yet.
 	api.Report()
 	fmt.Fprintln(ioutil.Discard, temps[0])
 }