f-29: stop: add a proper stop

Signed-off-by: GnomeZworc <nicolas.boufidjeline@g3e.fr>

pkg/worker/queue.go

@@ -1,13 +1,19 @@
 package worker
 
-import "log"
+import (
+	"log"
+	"sync"
+)
 
 // Task is a function to be executed asynchronously by a worker.
 type Task func()
 
 // Queue is a FIFO channel-backed task queue consumed by worker goroutines.
 type Queue struct {
-	tasks chan Task
+	tasks   chan Task
+	wg      sync.WaitGroup
+	mu      sync.RWMutex
+	stopped bool
 }
 
 // New creates a Queue with the given channel buffer size.
@@ -15,8 +21,16 @@ func New(bufferSize int) *Queue {
 	return &Queue{tasks: make(chan Task, bufferSize)}
 }
 
-// Submit enqueues a task. Blocks if the queue is full.
+// Submit enqueues a task. Blocks if the queue is full. Tasks submitted after
+// Stop are rejected and logged rather than enqueued.
 func (q *Queue) Submit(t Task) {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+
+	if q.stopped {
+		log.Print("worker: queue stopped, task rejected")
+		return
+	}
 	q.tasks <- t
 }
 
@@ -24,10 +38,28 @@ func (q *Queue) Submit(t Task) {
 func (q *Queue) Start(n int) {
 	log.Printf("worker: starting %d workers", n)
 	for i := range n {
+		q.wg.Add(1)
 		go func(id int) {
+			defer q.wg.Done()
 			for task := range q.tasks {
 				task()
 			}
 		}(i)
 	}
 }
+
+// Stop rejects new tasks, then waits for the queued and in-flight ones to
+// finish. The write lock is what makes closing the channel safe: it is only
+// taken once every in-flight Submit has released its read lock.
+func (q *Queue) Stop() {
+	q.mu.Lock()
+	if q.stopped {
+		q.mu.Unlock()
+		return
+	}
+	q.stopped = true
+	close(q.tasks)
+	q.mu.Unlock()
+
+	q.wg.Wait()
+}