create jobs queue for scheduling new builds

internal/queue/queue.go

@@ -0,0 +1,62 @@
+package queue
+
+import "sync"
+
+// Build is a request waiting for a worker
+type Build struct {
+	Pipeline string `json:"pipeline"`
+	Manifest string `json:"manifest"`
+}
+
+// Manifest contains additional metadata attached do a pipeline that are necessary for workers
+type Manifest struct {
+	destination string
+}
+
+// Job is an image build already in progress
+type Job struct {
+	UUID  string `json:"uuid"`
+	Build Build  `json:"build"`
+}
+
+// JobQueue contains already running jobs waiting for
+type JobQueue struct {
+	sync.Mutex
+	incomingBuilds chan Build     // Channel of incoming builds form Weldr API, we never want to block on this
+	waitingBuilds  []Build        // Unbounded FIFO queue of waiting builds
+	runningJobs    map[string]Job // Already running jobs, key is UUID
+}
+
+// NewJobQueue creates object of type JobQueue
+func NewJobQueue(timeout int, builds chan Build) *JobQueue {
+	jobs := &JobQueue{
+		incomingBuilds: builds,
+		waitingBuilds:  make([]Build, 0),
+		runningJobs:    make(map[string]Job),
+	}
+	go func() {
+		for {
+			// This call will block, do not put it inside the locked zone
+			newBuild := <-jobs.incomingBuilds
+			// Locking the whole job queue => as short as possible
+			jobs.Lock()
+			jobs.waitingBuilds = append(jobs.waitingBuilds, newBuild)
+			jobs.Unlock()
+		}
+	}()
+	return jobs
+}
+
+// StartNewJob starts a new job
+func (j *JobQueue) StartNewJob(id string, worker string) Job {
+	j.Lock()
+	newBuild := j.waitingBuilds[0]        // Take the first element
+	j.waitingBuilds = j.waitingBuilds[1:] // Discart 1st element
+	j.Unlock()
+	job := Job{
+		UUID:  id,
+		Build: newBuild,
+	}
+	j.runningJobs[id] = job
+	return job
+}