10 feat download queue (#59)

* testing message queue

* better mq syncronisation

* major code refactoring, concern separation.

* bugfix

* code refactoring

* queuesize configurable via flags

* code refactoring

* comments

* code refactoring, updated readme

server/internal/message_queue.go

@@ -0,0 +1,46 @@
+package internal
+
+import (
+	"log"
+
+	"github.com/marcopeocchi/yt-dlp-web-ui/server/config"
+)
+
+type MessageQueue struct {
+	ch         chan *Process
+	consumerCh chan struct{}
+}
+
+// Creates a new message queue.
+// By default it will be created with a size equals to nthe number of logical
+// CPU cores.
+// The queue size can be set via the qs flag.
+func NewMessageQueue() *MessageQueue {
+	size := config.Instance().GetConfig().QueueSize
+
+	if size <= 0 {
+		log.Fatalln("invalid queue size")
+	}
+
+	return &MessageQueue{
+		ch:         make(chan *Process, size),
+		consumerCh: make(chan struct{}, size),
+	}
+}
+
+// Publish a message to the queue and set the task to a peding state.
+func (m *MessageQueue) Publish(p *Process) {
+	go p.SetPending()
+	m.ch <- p
+}
+
+// Setup the consumer listened which "subscribes" to the queue events.
+func (m *MessageQueue) SetupConsumer() {
+	for msg := range m.ch {
+		m.consumerCh <- struct{}{}
+		go func(p *Process) {
+			p.Start()
+			<-m.consumerCh
+		}(msg)
+	}
+}