Use Channels to Handle Task Order.

Fixes: scipipe#81

process.go

@@ -316,29 +316,31 @@ func (p *Process) Run() {
 		Failf("%s: CoresPerTask (%d) can't be greater than maxConcurrentTasks of workflow (%d)\n", p.Name(), p.CoresPerTask, cap(p.workflow.concurrentTasks))
 	}
 
-	tasks := []*Task{}
-	for t := range p.createTasks() {
-		// Collect tasks so we can later wait for their done-signal before sending outputs
-		tasks = append(tasks, t)
-
-		// Sending FIFOs for the task
-		for oname, oip := range t.OutIPs {
-			if oip.doStream {
-				if oip.FifoFileExists() {
-					Fail("Fifo file exists, so exiting (clean up fifo files before restarting the workflow): ", oip.FifoPath())
+	tasks := make(chan *Task, BUFSIZE)
+	go func() {
+		defer close(tasks)
+		for t := range p.createTasks() {
+			tasks <- t
+
+			// Sending FIFOs for the task
+			for oname, oip := range t.OutIPs {
+				if oip.doStream {
+					if oip.FifoFileExists() {
+						Fail("Fifo file exists, so exiting (clean up fifo files before restarting the workflow): ", oip.FifoPath())
+					}
+					oip.CreateFifo()
+					p.Out(oname).Send(oip)
 				}
-				oip.CreateFifo()
-				p.Out(oname).Send(oip)
 			}
-		}
 
-		// Execute task in separate go-routine
-		go t.Execute()
-	}
+			// Execute task in separate go-routine
+			go t.Execute()
+		}
+	}()
 
 	// Wait for tasks to finish, in the order they were started (thus maintaining
 	// order of IPs), and then sending output IPs
-	for _, t := range tasks {
+	for t := range tasks {
 		<-t.Done
 		for oname, oip := range t.OutIPs {
 			if !oip.doStream { // Streaming (FIFO) outputs have been sent earlier