Feat/stateful goroutines exercise

.gitignore

@@ -30,4 +30,8 @@ go.work.sum
 # Editor/IDE
 # .idea/
 # .vscode/
-bin/
+bin/
+
+# Codacy
+.codacy/
+.github/instructions/

internal/exercises/catalog.yaml

@@ -134,6 +134,14 @@ concepts:
   test_regex: ".*"
   hints:
     - Define a custom error type and return it from a function.
+- slug: 28_stateful_goroutines
+  title: Stateful Goroutines
+  test_regex: ".*"
+  hints:
+    - Use channels to send read and write operations to a state-owning goroutine.
+    - Create readOp and writeOp structs with response channels.
+    - The state-owning goroutine uses select to handle operations from channels.
+    - This pattern avoids mutexes by ensuring only one goroutine accesses shared state.
 - slug: 37_xml
   title: XML Encoding and Decoding
   test_regex: ".*"

internal/exercises/solutions/28_stateful_goroutines/stateful_goroutines.go

@@ -0,0 +1,60 @@
+package stateful_goroutines
+
+// readOp represents a read request
+type readOp struct {
+	resp chan int
+}
+
+// writeOp represents a write request (increment)
+type writeOp struct {
+	amount int
+	resp   chan bool
+}
+
+type Counter struct {
+	reads  chan readOp
+	writes chan writeOp
+}
+
+// NewCounter creates and starts a new stateful counter
+func NewCounter() *Counter {
+	c := &Counter{
+		reads:  make(chan readOp),
+		writes: make(chan writeOp),
+	}
+
+	// Start the state-owning goroutine
+	go func() {
+		var state int
+		for {
+			select {
+			case read := <-c.reads:
+				read.resp <- state
+			case write := <-c.writes:
+				state += write.amount
+				write.resp <- true
+			}
+		}
+	}()
+
+	return c
+}
+
+// Increment increments the counter by the given amount
+func (c *Counter) Increment(amount int) {
+	write := writeOp{
+		amount: amount,
+		resp:   make(chan bool),
+	}
+	c.writes <- write
+	<-write.resp
+}
+
+// GetValue returns the current counter value
+func (c *Counter) GetValue() int {
+	read := readOp{
+		resp: make(chan int),
+	}
+	c.reads <- read
+	return <-read.resp
+}

internal/exercises/templates/28_stateful_goroutines/stateful_goroutines.go

@@ -0,0 +1,40 @@
+package stateful_goroutines
+
+// TODO:
+// - Implement a Counter that manages state using a single goroutine and channels.
+// - The counter should support Increment and GetValue operations.
+// - State must be owned by a single goroutine to avoid race conditions.
+// - Other goroutines communicate via channels to read or modify the state.
+
+// readOp represents a read request
+type readOp struct {
+	resp chan int
+}
+
+// writeOp represents a write request (increment)
+type writeOp struct {
+	amount int
+	resp   chan bool
+}
+
+type Counter struct {
+	reads  chan readOp
+	writes chan writeOp
+}
+
+// NewCounter creates and starts a new stateful counter
+func NewCounter() *Counter {
+	// TODO: initialize channels and start the state-owning goroutine
+	return &Counter{}
+}
+
+// Increment increments the counter by the given amount
+func (c *Counter) Increment(amount int) {
+	// TODO: send a write operation and wait for confirmation
+}
+
+// GetValue returns the current counter value
+func (c *Counter) GetValue() int {
+	// TODO: send a read operation and return the value
+	return 0
+}

internal/exercises/templates/28_stateful_goroutines/stateful_goroutines_test.go

@@ -0,0 +1,113 @@
+package stateful_goroutines
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestCounterInitialization(t *testing.T) {
+	counter := NewCounter()
+	if counter == nil {
+		t.Fatal("NewCounter() returned nil")
+	}
+
+	// Give goroutine time to start
+	time.Sleep(10 * time.Millisecond)
+
+	value := counter.GetValue()
+	if value != 0 {
+		t.Errorf("Initial counter value = %d, want 0", value)
+	}
+}
+
+func TestCounterIncrement(t *testing.T) {
+	counter := NewCounter()
+
+	counter.Increment(5)
+	counter.Increment(3)
+
+	value := counter.GetValue()
+	if value != 8 {
+		t.Errorf("Counter value = %d, want 8", value)
+	}
+}
+
+func TestCounterConcurrentIncrements(t *testing.T) {
+	counter := NewCounter()
+
+	var wg sync.WaitGroup
+	numGoroutines := 100
+	incrementsPerGoroutine := 10
+
+	for i := 0; i < numGoroutines; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < incrementsPerGoroutine; j++ {
+				counter.Increment(1)
+			}
+		}()
+	}
+
+	wg.Wait()
+
+	expected := numGoroutines * incrementsPerGoroutine
+	value := counter.GetValue()
+	if value != expected {
+		t.Errorf("Counter value = %d, want %d", value, expected)
+	}
+}
+
+func TestCounterConcurrentReadsAndWrites(t *testing.T) {
+	counter := NewCounter()
+
+	var wg sync.WaitGroup
+	numReaders := 50
+	numWriters := 50
+
+	// Start writers
+	for i := 0; i < numWriters; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < 5; j++ {
+				counter.Increment(1)
+				time.Sleep(time.Microsecond)
+			}
+		}()
+	}
+
+	// Start readers
+	for i := 0; i < numReaders; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < 5; j++ {
+				_ = counter.GetValue()
+				time.Sleep(time.Microsecond)
+			}
+		}()
+	}
+
+	wg.Wait()
+
+	// Verify final value
+	expected := numWriters * 5
+	value := counter.GetValue()
+	if value != expected {
+		t.Errorf("Counter value = %d, want %d", value, expected)
+	}
+}
+
+func TestCounterNegativeIncrement(t *testing.T) {
+	counter := NewCounter()
+
+	counter.Increment(10)
+	counter.Increment(-3)
+
+	value := counter.GetValue()
+	if value != 7 {
+		t.Errorf("Counter value = %d, want 7", value)
+	}
+}