first

course/13-channels/exercises/5-close/code.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func countReports(numSentCh chan int) int {
+	// ?
+}
+
+// TEST SUITE - Don't touch below this line
+
+func test(numBatches int) {
+	numSentCh := make(chan int)
+	go sendReports(numBatches, numSentCh)
+
+	fmt.Println("Start counting...")
+	numReports := countReports(numSentCh)
+	fmt.Printf("%v reports sent!\n", numReports)
+	fmt.Println("========================")
+}
+
+func main() {
+	test(3)
+	test(4)
+	test(5)
+	test(6)
+}
+
+func sendReports(numBatches int, ch chan int) {
+	for i := 0; i < numBatches; i++ {
+		numReports := i*23 + 32%17
+		ch <- numReports
+		fmt.Printf("Sent batch of %v reports\n", numReports)
+		time.Sleep(time.Millisecond * 100)
+	}
+	close(ch)
+}

course/13-channels/exercises/5-close/complete.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func countReports(numSentCh chan int) int {
+	total := 0
+	for {
+		numSent, ok := <-numSentCh
+		if !ok {
+			break
+		}
+		total += numSent
+	}
+	return total
+}
+
+// TEST SUITE - Don't touch below this line
+
+func test(numBatches int) {
+	numSentCh := make(chan int)
+	go sendReports(numBatches, numSentCh)
+
+	fmt.Println("Start counting...")
+	numReports := countReports(numSentCh)
+	fmt.Printf("%v reports sent!\n", numReports)
+	fmt.Println("========================")
+}
+
+func main() {
+	test(3)
+	test(4)
+	test(5)
+	test(6)
+}
+
+func sendReports(numBatches int, ch chan int) {
+	for i := 0; i < numBatches; i++ {
+		numReports := i*23 + 32%17
+		ch <- numReports
+		fmt.Printf("Sent batch of %v reports\n", numReports)
+		time.Sleep(time.Millisecond * 100)
+	}
+	close(ch)
+}

course/13-channels/exercises/5-close/expected.txt

@@ -0,0 +1,30 @@
+Start counting...
+Sent batch of 15 reports
+Sent batch of 38 reports
+Sent batch of 61 reports
+114 reports sent!
+========================
+Start counting...
+Sent batch of 15 reports
+Sent batch of 38 reports
+Sent batch of 61 reports
+Sent batch of 84 reports
+198 reports sent!
+========================
+Start counting...
+Sent batch of 15 reports
+Sent batch of 38 reports
+Sent batch of 61 reports
+Sent batch of 84 reports
+Sent batch of 107 reports
+305 reports sent!
+========================
+Start counting...
+Sent batch of 15 reports
+Sent batch of 38 reports
+Sent batch of 61 reports
+Sent batch of 84 reports
+Sent batch of 107 reports
+Sent batch of 130 reports
+435 reports sent!
+========================

course/13-channels/exercises/5-close/readme.md

@@ -0,0 +1,40 @@
+# Closing channels in Go
+
+Channels can be explicitly closed by a *sender*:
+
+```go
+ch := make(chan int)
+
+// do some stuff with the channel
+
+close(ch)
+```
+
+## Checking if a channel is closed
+
+Similar to the `ok` value when accessing data in a `map`, receivers can check the `ok` value when receiving from a channel to test if a channel was closed.
+
+```go
+v, ok := <-ch
+```
+
+ok is `false` if the channel is empty and closed.
+
+## Don't send on a closed channel
+
+Sending on a closed channel will cause a panic. A panic on the main goroutine will cause the entire program to crash, and a panic in any other goroutine will cause *that goroutine* to crash.
+
+Closing isn't necessary. There's nothing wrong with leaving channels open, they'll still be garbage collected if they're unused. You should close channels to indicate explicitly to a receiver that nothing else is going to come across.
+
+## Assignment
+
+At Mailio we're all about keeping track of what our systems are up to with great logging and [telemetry](https://en.wikipedia.org/wiki/Telemetry).
+
+The `sendReports` function sends out a batch of reports to our clients and reports back how many were sent across a channel. It closes the channel when it's done.
+
+Complete the `countReports` function. It should:
+
+* Use an infinite `for` loop to read from the channel:
+* If the channel is closed, break out of the loop
+* Otherwise, keep a running total of the number of reports sent
+* Return the total number of reports sent