v0.3.0 write output on its own goroutine, blocked terminal report

writer.go

@@ -0,0 +1,56 @@
+package terminal
+
+import "time"
+
+// sendLocked queues what the operation in progress rendered and wakes the writer.
+// Caller MUST hold mu.
+func (t *termImpl) sendLocked() {
+	buf := &t.output.buf
+	if buf.Len() == 0 {
+		return
+	}
+	t.queued = append(t.queued, buf.Bytes()...)
+	buf.Reset()
+	select {
+	case t.wake <- struct{}{}:
+	default:
+	}
+}
+
+// writeLoop is the only writer of terminal output after Init. It returns once Fini
+// has queued the restoring sequences and they are written; a terminal that never
+// takes them leaves it in its write, and Fini stops waiting.
+func (t *termImpl) writeLoop() {
+	defer close(t.writerDone)
+	for {
+		select {
+		case <-t.wake:
+			t.drain()
+		case <-t.quit:
+			t.drain()
+			return
+		}
+	}
+}
+
+// drain writes what is queued until nothing is, and draws a frame held while a
+// write was out once that write returns. The write runs without mu, so whoever
+// draws meanwhile finds writeSince set and holds its frame instead of waiting.
+func (t *termImpl) drain() {
+	t.mu.Lock()
+	for {
+		if len(t.queued) == 0 {
+			t.releaseLocked()
+		}
+		if len(t.queued) == 0 {
+			break
+		}
+		t.writing, t.queued = t.queued, t.writing[:0]
+		t.writeSince.Store(time.Now().UnixNano())
+		t.mu.Unlock()
+		_ = t.backend.Write(t.writing) // a failed write is lost, as one through a buffered writer was
+		t.writeSince.Store(0)
+		t.mu.Lock()
+	}
+	t.mu.Unlock()
+}